Showing 1–50 of 50 results for author: Dubs, C

k-Selective Electrical-to-Magnon Transduction with Realistic Field-distributed Nanoantennas

Authors: Andreas Höfinger, Andrey A. Voronov, David Schmoll, Sabri Koraltan, Florian Bruckner, Claas Abert, Dieter Suess, Morris Lindner, Timmy Reimann, Carsten Dubs, Andrii V. Chumak, Sebastian Knauer

Abstract: The excitation and detection of propagating spin waves with lithographed nanoantennas underpin both classical magnonic circuits and emerging quantum technologies. Here, we establish a framework for all-electrical propagating spin-wave spectroscopy (AEPSWS) that links realistic electromagnetic drive fields to micromagnetic dynamics. Using finite-element (FE) simulations, we compute the full vector… ▽ More The excitation and detection of propagating spin waves with lithographed nanoantennas underpin both classical magnonic circuits and emerging quantum technologies. Here, we establish a framework for all-electrical propagating spin-wave spectroscopy (AEPSWS) that links realistic electromagnetic drive fields to micromagnetic dynamics. Using finite-element (FE) simulations, we compute the full vector near-field of electrical impedance-matched, tapered coplanar and stripline antennas and import this distribution into finite-difference (FD) micromagnetic solvers. This approach captures the antenna-limited wave-vector spectrum and the component-selective driving fields (perpendicular to the static magnetisation) that simplified uniform-field models cannot. From this coupling, we derive how realistic current return paths and tapering shapes, k-weighting functions, for Damon-Eshbach surface spin waves in yttrium-iron-garnet (YIG) films are, for millimetre-scale matched CPWs and linear tapers down to nanometre-scale antennas. Validation against experimental AEPSWS on a $48\,nm$ YIG film shows quantitative agreement in dispersion ridges, group velocities, and spectral peak positions, establishing that the antenna acts as a tunable k-space filter. These results provide actionable design rules for on-chip magnonic transducers, with immediate relevance for low-power operation regimes and prospective applications in quantum magnonics. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Magnetic Materials for Quantum Magnonics

Authors: Rostyslav O. Serha, Carsten Dubs, Andrii V. Chumak

Abstract: Quantum magnonics studies the quantum properties of magnons, the quanta of spin waves, and their application in quantum information processing. Progress in this field depends on identifying magnetic materials with characteristics tailored to the diverse requirements of magnonics and quantum magnonics. For single-magnon excitation, its control, hybrid coupling, and entanglement, the most critical p… ▽ More Quantum magnonics studies the quantum properties of magnons, the quanta of spin waves, and their application in quantum information processing. Progress in this field depends on identifying magnetic materials with characteristics tailored to the diverse requirements of magnonics and quantum magnonics. For single-magnon excitation, its control, hybrid coupling, and entanglement, the most critical property is the ability to support long magnon lifetimes. This perspective reviews established and emerging magnetic materials, including ferromagnetic metals, Heusler compounds, antiferromagnets, altermagnets, organic and 2D van der Waals magnets, hexaferrites, and in particular yttrium iron garnet (YIG), highlighting their key characteristics. YIG remains the benchmark, with bulk crystals supporting sub-microsecond Kittel-mode lifetimes and ultra-pure spheres achieving $\sim18\,μ$s for dipolar-exchange magnons at millikelvin temperatures. However, thin YIG films on gadolinium gallium garnet (GGG) substrates suffer from severe lifetime reduction due to substrate-induced losses. In contrast, YIG films on a new lattice matched, diamagnetic alternative, yttrium scandium gallium/aluminum garnet (YSGAG), overcomes these limitations and preserves low magnetic damping down to millikelvin temperatures. These advances provide a practical pathway toward ultralong-living magnons in thin films, enabling scalable quantum magnonics with coherent transport, strong magnon-photon, magnon-qubit coupling, and integrated quantum networks. △ Less

Submitted 10 October, 2025; originally announced October 2025.

All-magnonic neurons for analog artificial neural networks

Authors: David Breitbach, Moritz Bechberger, Hanadi Mortada, Björn Heinz, Roman Verba, Qi Wang, Carsten Dubs, Mario Carpentieri, Giovanni Finocchio, Davi Rodrigues, Alexandre Abbass Hamadeh, Philipp Pirro

Abstract: Analog neuromorphic hardware is gaining traction as conventional digital systems struggle to keep pace with the growing energy and scalability demands of modern neural networks. Here, we present analog, fully magnonic, artificial neurons, which exploit a nonlinear magnon excitation mechanism based on the nonlinear magnonic frequency shift. This yields a sharp trigger response and tunable fading me… ▽ More Analog neuromorphic hardware is gaining traction as conventional digital systems struggle to keep pace with the growing energy and scalability demands of modern neural networks. Here, we present analog, fully magnonic, artificial neurons, which exploit a nonlinear magnon excitation mechanism based on the nonlinear magnonic frequency shift. This yields a sharp trigger response and tunable fading memory, as well as synaptic connections to other neurons via propagating magnons. Using micro-focused Brillouin light scattering spectroscopy on a Gallium-substituted yttrium iron garnet thin film, we show multi-neuron triggering, cascadability, and multi-input integration across interconnected neurons. Finally, we implement the experimentally verified neuron activation function in a neural network simulation, yielding high classification accuracy on standard benchmarks. The results establish all-magnonic neurons as promising devices for scalable, low-power, wave-based neuromorphic computing, highlighting their potential as building blocks for future physical neural networks. △ Less

Submitted 22 September, 2025; originally announced September 2025.

Comments: 17 pages, 6 figures

Exchange spin-wave propagation in Ga:YIG nanowaveguides

Authors: Andrey A. Voronov, Khrystyna O. Levchenko, Roman Verba, Kristýna Davídková, Carsten Dubs, Michal Urbánek, Qi Wang, Dieter Suess, Claas Abert, Andrii V. Chumak

Abstract: Spin-wave-based computing has emerged as a promising approach to overcome the fundamental limitations of CMOS technologies. However, the increasing demand for device miniaturization down to a 100 nm scale presents significant challenges for long-distance spin-wave transport. Gallium-substituted yttrium iron garnet (Ga:YIG) offers a potential solution to these challenges due to its unique magnetic… ▽ More Spin-wave-based computing has emerged as a promising approach to overcome the fundamental limitations of CMOS technologies. However, the increasing demand for device miniaturization down to a 100 nm scale presents significant challenges for long-distance spin-wave transport. Gallium-substituted yttrium iron garnet (Ga:YIG) offers a potential solution to these challenges due to its unique magnetic properties. The reduced saturation magnetization in Ga:YIG enables efficient excitation of exchange-dominated spin waves, which exhibit enhanced transport characteristics compared to dipolar-dominated modes in conventional materials. Here, we present the first comprehensive study combining experimental, analytical, and numerical investigations of spin-wave propagation in Ga:YIG waveguides down to 145 nm width and 73 nm thickness. Using micro-focused Brillouin light scattering spectroscopy, TetraX simulations, and analytical dispersion calculations, we demonstrate that Ga:YIG waveguides support spin waves with significantly higher group velocities up to 600 m/s. This value remains constant for structures with different widths, leading to longer spin-wave propagation lengths in nanowaveguides compared to non-substituted YIG. These results reveal that gallium substitution provides access to faster and longer-lived spin waves, opening new possibilities for implementing this material in nanoscale magnonic devices. △ Less

Submitted 8 September, 2025; v1 submitted 5 September, 2025; originally announced September 2025.

YSGAG: The Ideal Substrate for YIG in Quantum Magnonics

Authors: Rostyslav O. Serha, Carsten Dubs, Christo Guguschev, Bernd Aichner, David Schmoll, Julien Schäfer, Jaganandha Panda, Matthias Weiler, Philipp Pirro, Michal Urbánek, Andrii V. Chumak

Abstract: Quantum magnonics leverages the quantum properties of magnons to advance nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), known for exceptionally long magnon lifetimes, is a cornerstone material typically grown as thin films on gadolinium gallium garnet (GGG) for lattice matching. However, paramagnetic GGG introduces detrimental damping at low temperatures due t… ▽ More Quantum magnonics leverages the quantum properties of magnons to advance nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), known for exceptionally long magnon lifetimes, is a cornerstone material typically grown as thin films on gadolinium gallium garnet (GGG) for lattice matching. However, paramagnetic GGG introduces detrimental damping at low temperatures due to substrate magnetization, undermining quantum applications. Here, we study magnetic damping in a 150$\,$nm-thick YIG film on a yttrium scandium gallium aluminum garnet (YSGAG) substrate, a newly developed diamagnetic alternative to GGG. Using ferromagnetic resonance spectroscopy down to 30$\,$mK, we compare YIG/YSGAG with a conventional YIG/GGG reference system. We demonstrate that the YIG/YSGAG system maintains low damping from 300$\,$K to 30$\,$mK, with $α= 4.29\times10^{-5}$ at room temperature, comparable to the best YIG/GGG films and bulk YIG, with no low-temperature upturn. The diamagnetic substrate eliminates the dissipation mechanisms that dominate on magnetized GGG, preserving low magnetic damping across the full temperature range. Consequently, YSGAG serves as an ideal substrate for YIG films in quantum magnonics and is paving the way for the development of spin-wave-based quantum technologies. △ Less

Submitted 10 November, 2025; v1 submitted 26 August, 2025; originally announced August 2025.

Novel diamagnetic garnet-type substrate single crystals for ultralow-damping yttrium iron garnet Y3Fe5O12 films at cryogenic temperatures

Authors: C. Guguschev, C. Dubs, R. Blukis, O. Surzhenko, M. Brützam, R. Koc, C. Rhode, K. Berger, C. Richter, C. Berryman, R. O. Serha, A. V. Chumak

Abstract: Y3Sc2Ga3O12-Y3Sc2Al3O12 and Y3Sc2Ga3O12-Y3Al5O12 (YSGAG) solid solution single crystals with diameters up to 30 mm and total lengths up to about 100 mm were grown by the conventional Czochralski technique. Rocking curve measurements on polished sections revealed typical FWHM values of about 22 arcsec, which is indicative of relatively high structural quality for a solid-solution crystal. The grown… ▽ More Y3Sc2Ga3O12-Y3Sc2Al3O12 and Y3Sc2Ga3O12-Y3Al5O12 (YSGAG) solid solution single crystals with diameters up to 30 mm and total lengths up to about 100 mm were grown by the conventional Czochralski technique. Rocking curve measurements on polished sections revealed typical FWHM values of about 22 arcsec, which is indicative of relatively high structural quality for a solid-solution crystal. The grown substrate crystals are nearly lattice-matched with Y3Fe5O12 (YIG) to allow epitaxial growth of high-quality thin films. Single crystalline YIG films with thicknesses between 100 nanometer and 2.9 micrometer were successfully grown on epi-polished YSGAG substrates using liquid phase epitaxy (LPE). Selected magnetic and microwave properties of the epitaxial films, which still exhibit small lattice misfits to the substrates, were then studied at room temperature. In addition, initial low-temperature investigations confirm that the YIG/YSGAG system is superior to the conventional YIG/GGG (Gd3Ga5O12) system at temperatures below 10 K, as the ferromagnetic resonance (FMR) linewidth does not increase with decreasing temperature. Therefore, the novel diamagnetic substrates are better suited for microwave applications at low temperature, as excessive damping losses induced by paramagnetic substrates can be avoided. It therefore seems to be a suitable pathway to achieve scalable microwave components for hybrid-integrated quantum systems based on ultralow-damping YIG films that can operate efficiently at millikelvin temperatures. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 25 pages, 16 figures, 4 tables

1D YIG hole-based magnonic nanocrystal

Authors: K. O. Levchenko, K. Davídková, R. O. Serha, M. Moalic, A. A. Voronov, C. Dubs, O. Surzhenko, M. Lindner, J. Panda, Q. Wang, O. Wojewoda, B. Heinz, M. Urbánek, M. Krawczyk, A. V. Chumak

Abstract: Magnetic media with artificial periodic modulation-magnonic crystals (MCs) - enable tunable spin-wave dynamics and band structure engineering. Nanoscaling enhances these capabilities, making magnonic nanocrystals promising for both fundamental studies and applications. Here, we report on the design, fabrication, and characterization of one-dimensional YIG MCs with nanoholes ($d \approx $ 150 nm) s… ▽ More Magnetic media with artificial periodic modulation-magnonic crystals (MCs) - enable tunable spin-wave dynamics and band structure engineering. Nanoscaling enhances these capabilities, making magnonic nanocrystals promising for both fundamental studies and applications. Here, we report on the design, fabrication, and characterization of one-dimensional YIG MCs with nanoholes ($d \approx $ 150 nm) spaced $a \approx 1 μ$m apart. Micro-focused Brillouin light scattering and propagating spin-wave spectroscopy, supported by TetraX and MuMax$^3$ simulations, reveal spin-wave transmission over 5 $μ$m in the Damon-Eshbach configuration, and the formation of pronounced band gaps with rejection levels up to 26 dB. Detailed analysis of the spin-wave dispersion uncovered complex mode interactions, including two prominent anticrossings at 3.1 and 18.7 rad/$μ$m, between which the spin-wave energy is predominantly carried by the $n$ = 2 mode, enabling efficient transmission. The results advance the development of functional MCs and open pathways toward 2D magnonic nanoarrays and magnonic RF nanodevices. △ Less

Submitted 12 June, 2025; originally announced June 2025.

Comments: Manuscript: 6 pages, 4 figures; Supplementary materials: 12 pages, 11 figures

Ultra-long-living magnons in the quantum limit

Authors: Rostyslav O. Serha, Kaitlin H. McAllister, Fabian Majcen, Sebastian Knauer, Timmy Reimann, Carsten Dubs, Gennadii A. Melkov, Alexander A. Serga, Vasyl S. Tyberkevych, Andrii V. Chumak, Dmytro A. Bozhko

Abstract: Coherence time is a key property of quantum systems, determining how long quantum information can be preserved. In solid-state platforms, this parameter is closely linked to the lifetime of quasiparticles that can store quantum information. For decades, magnons - quasiparticles arising from collective magnetization dynamics - have exhibited lifetimes below one microsecond at gigahertz frequencies,… ▽ More Coherence time is a key property of quantum systems, determining how long quantum information can be preserved. In solid-state platforms, this parameter is closely linked to the lifetime of quasiparticles that can store quantum information. For decades, magnons - quasiparticles arising from collective magnetization dynamics - have exhibited lifetimes below one microsecond at gigahertz frequencies, limiting their viability as quantum information carriers. Here, we report the discovery of short-wavelength magnons with lifetimes exceeding 18 μs at millikelvin temperatures. The experiment was performed on an ultra-pure single-crystal Yttrium Iron Garnet (YIG) sphere over a wide temperature range, from ambient down to 30 mK. These results directly confirm the theoretical prediction that the magnon lifetime in an ideal YIG crystal at zero temperature is infinite, paving the way for the engineering of lossless magnetic systems in which magnons will be employed as long-lived carriers of information for quantum gates and quantum storage. △ Less

Submitted 16 September, 2025; v1 submitted 28 May, 2025; originally announced May 2025.

Magnetically Compensated Nanometer-thin Ga-Substituted Yttrium Iron Garnet (Ga:YIG) Films with Robust Perpendicular Magnetic Anisotropy

Authors: Carsten Dubs, Oleksii Surzhenko

Abstract: Magnetically full or partially compensated insulating ferrimagnets with perpendicular magnetic anisotropy (PMA) offer valuable insights into fundamental spin-wave physics and high-speed magnonic applications. This study reports on key magnetic parameters of nanometer-thin Ga substituted yttrium iron garnet (Ga:YIG) films with saturation magnetization 4PiMs below 200 G. Vibrating sample magnetometr… ▽ More Magnetically full or partially compensated insulating ferrimagnets with perpendicular magnetic anisotropy (PMA) offer valuable insights into fundamental spin-wave physics and high-speed magnonic applications. This study reports on key magnetic parameters of nanometer-thin Ga substituted yttrium iron garnet (Ga:YIG) films with saturation magnetization 4PiMs below 200 G. Vibrating sample magnetometry (VSM) is used to determine the remanent magnetization 4PiMr and the polar orientation of the magnetic easy axis in samples with very low net magnetic moments. Additionally, the temperature dependence of the net magnetization of magnetically compensated Ga:YIG films, with compensation points Tcomp near room temperature is investigated. For films with remanent magnetization values below 60 G at room temperature, the compensation points Tcomp are determined and correlated with their Curie temperatures TC. Ferromagnetic resonance (FMR) measurements at 6.5 GHz show that the FMR linewidths Delta H FWHM correlate inversely proportional with the remanent magnetization. The reduced saturation magnetization in the Ga:YIG films leads to a significant increase in the effective magnetization 4PiMeff and thus enables films with robust PMA. This opens up a new parameter space for the fine-tuning of potential magnonic spin-wave devices on commonly used GGG substrates. △ Less

Submitted 4 April, 2025; originally announced April 2025.

Comments: main text: 18 pages, 6 figures, Supporting Information: 6 pages, 1 figure, 2 tables

Elimination of substrate-induced FMR linewidth broadening in the epitaxial system YIG-GGG by microstructuring

Authors: David Schmoll, Rostyslav O. Serha, Jaganandha Panda, Andrey A. Voronov, Carsten Dubs, Michal Urbánek, Andrii V. Chumak

Abstract: Modern quantum technologies and hybrid quantum systems offer the opportunity to utilize magnons on the level of single excitations. Long lifetimes, low decoherence rates, and a strong coupling rate to other subsystems propose the ferrimagnet yttrium iron garnet (YIG), grown on a gadolinium gallium garnet (GGG) substrate, as a suitable platform to host magnonic quantum states. However, the magnetic… ▽ More Modern quantum technologies and hybrid quantum systems offer the opportunity to utilize magnons on the level of single excitations. Long lifetimes, low decoherence rates, and a strong coupling rate to other subsystems propose the ferrimagnet yttrium iron garnet (YIG), grown on a gadolinium gallium garnet (GGG) substrate, as a suitable platform to host magnonic quantum states. However, the magnetic damping at cryogenic temperatures significantly increases due to the paramagnetic character and the highly inhomogeneous stray field of GGG, as recent experiments and simulations pointed out. Here, we report on temperature dependent ferromagnetic resonance (FMR) spectroscopy studies in YIG-GGG thin-films with different sample geometries. We experimentally demonstrate how to eliminate the asymmetric stray field-induced linewidth broadening via microstructuring of the YIG film. Additionally, our experiments reveal evidence of a non-Gilbert like behavior of the linewidth at cryogenic temperatures, independent of the inhomogeneous GGG stray field. △ Less

Submitted 5 February, 2025; originally announced February 2025.

Comments: 8 pages, 3 figures

YIG/CoFeB bilayer magnonic diode

Authors: Noura Zenbaa, Khrystyna O. Levchenko, Jaganandha Panda, Kristýna Davídková, Moritz Ruhwedel, Sebastian Knauer, Morris Lindner, Carsten Dubs, Qi Wang, Michal Urbánek, Philipp Pirro, Andrii V. Chumak

Abstract: We demonstrate a magnonic diode based on a bilayer structure of Yttrium Iron Garnet (YIG) and Cobalt Iron Boron (CoFeB). The bilayer exhibits pronounced non-reciprocal spin-wave propagation, enabled by dipolar coupling and the magnetic properties of the two layers. The YIG layer provides low damping and efficient spin-wave propagation, while the CoFeB layer introduces strong magnetic anisotropy, c… ▽ More We demonstrate a magnonic diode based on a bilayer structure of Yttrium Iron Garnet (YIG) and Cobalt Iron Boron (CoFeB). The bilayer exhibits pronounced non-reciprocal spin-wave propagation, enabled by dipolar coupling and the magnetic properties of the two layers. The YIG layer provides low damping and efficient spin-wave propagation, while the CoFeB layer introduces strong magnetic anisotropy, critical for achieving diode functionality. Experimental results, supported by numerical simulations, show unidirectional propagation of Magnetostatic Surface Spin Waves (MSSW), significantly suppressing backscattered waves. This behavior was confirmed through wavevector-resolved and micro-focused Brillouin Light Scattering measurements and is supported by numerical simulations. The proposed YIG/SiO$_2$/CoFeB bilayer magnonic diode demonstrates the feasibility of leveraging non-reciprocal spin-wave dynamics for functional magnonic devices, paving the way for energy-efficient, wave-based signal processing technologies. △ Less

Submitted 11 December, 2024; originally announced December 2024.

Damping Enhancement in YIG at Millikelvin Temperatures due to GGG Substrate

Authors: Rostyslav O. Serha, Andrey A. Voronov, David Schmoll, Rebecca Klingbeil, Sebastian Knauer, Sabri Koraltan, Ekaterina Pribytova, Morris Lindner, Timmy Reimann, Carsten Dubs, Claas Abert, Roman Verba, Michal Urbánek, Dieter Suess, Andrii V. Chumak

Abstract: Quantum magnonics aims to exploit the quantum mechanical properties of magnons for nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), which offers the longest magnon lifetimes, is a key material typically grown on gadolinium gallium garnet (GGG) substrates for structural compatibility. However, the increased magnetic damping in YIG/GGG systems below 50$\,$K poses… ▽ More Quantum magnonics aims to exploit the quantum mechanical properties of magnons for nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), which offers the longest magnon lifetimes, is a key material typically grown on gadolinium gallium garnet (GGG) substrates for structural compatibility. However, the increased magnetic damping in YIG/GGG systems below 50$\,$K poses a challenge for quantum applications. Here, we study the damping in a 97$\,$nm-thick YIG film on a 500$\,μ$m-thick GGG substrate at temperatures down to 30$\,$mK using ferromagnetic resonance (FMR) spectroscopy. We show that the dominant physical mechanism for the observed tenfold increase in FMR linewidth at millikelvin temperatures is the non-uniform bias magnetic field generated by the partially magnetized paramagnetic GGG substrate. Numerical simulations and analytical theory show that the GGG-driven linewidth enhancement can reach up to 6.7 times. In addition, at low temperatures and frequencies above 18$\,$GHz, the FMR linewidth deviates from the viscous Gilbert-damping model. These results allow the partial elimination of the damping mechanisms attributed to GGG, which is necessary for the advancement of solid-state quantum technologies. △ Less

Submitted 3 December, 2024; originally announced December 2024.

Journal ref: Materials Today Quantum 5, 100025 (2025)

Fast switchable unidirectional magnon emitter

Authors: Yueqi Wang, Mengying Guo, Kristýna Davídková, Roman Verba, Xueyu Guo, Carsten Dubs, Andrii V. Chumak, Philipp Pirro, Qi Wang

Abstract: Magnon spintronics is an emerging field that explores the use of magnons, the quanta of spin waves in magnetic materials for information processing and communication. Achieving unidirectional information transport with fast switching capability is critical for the development of fast integrated magnonic circuits, which offer significant advantages in high-speed, low-power information processing. H… ▽ More Magnon spintronics is an emerging field that explores the use of magnons, the quanta of spin waves in magnetic materials for information processing and communication. Achieving unidirectional information transport with fast switching capability is critical for the development of fast integrated magnonic circuits, which offer significant advantages in high-speed, low-power information processing. However, previous unidirectional information transport has primarily focused on Damon-Eshbach spin wave modes, which are non-switchable as their propagation direction is defined by the direction of the external field and cannot be changed in a short time. Here, we experimentally demonstrate a fast switchable unidirectional magnon emitter in the forward volume spin wave mode by a current-induced asymmetric Oersted field. Our findings reveal significant nonreciprocity and nanosecond switchability, underscoring the potential of the method to advance high-speed spin-wave processing networks. △ Less

Submitted 2 October, 2024; originally announced October 2024.

Comments: 15 pages, 4 figures

All-magnonic repeater based on bistability

Authors: Qi Wang, Roman Verba, Kristyna Davidkova, Bjorn Heinz, Shixian Tian, Yiheng Rao, Mengying Guo, Xueyu Guo, Carsten Dubs, Philipp Pirro, Andrii V. Chumak

Abstract: Bistability, a universal phenomenon found in diverse fields such as biology, chemistry, and physics, describes a scenario in which a system has two stable equilibrium states and resets to one of the two states. The ability to switch between these two states is the basis for a wide range of applications, particularly in memory and logic operations. Here, we present a universal approach to achieve b… ▽ More Bistability, a universal phenomenon found in diverse fields such as biology, chemistry, and physics, describes a scenario in which a system has two stable equilibrium states and resets to one of the two states. The ability to switch between these two states is the basis for a wide range of applications, particularly in memory and logic operations. Here, we present a universal approach to achieve bistable switching in magnonics, the field processing data using spin waves. As an exemplary application, we use magnonic bistability to experimentally demonstrate the still missing magnonic repeater. A pronounced bistable window is observed in a 1um wide magnonic conduit under an external rf drive characterized by two magnonic stable states defined as low and high spin-wave amplitudes. The switching between these two states is realized by another propagating spin wave sent into the rf driven region. This magnonic bistable switching is used to design the magnonic repeater, which receives the original decayed and distorted spin wave and regenerates a new spin wave with amplified amplitude and normalized phase. Our magnonic repeater is proposed to be installed at the inputs of each magnonic logic gate to overcome the spin-wave amplitude degradation and phase distortion during previous propagation and achieve integrated magnonic circuits or magnonic neuromorphic networks. △ Less

Submitted 19 March, 2024; originally announced March 2024.

Comments: 13 pages, 4 figures

Generation of gigahertz frequency surface acoustic waves in YIG/ZnO heterostructures

Authors: Finlay Ryburn, Kevin Künstle, Yangzhan Zhang, Yannik Kunz, Timmy Reimann, Morris Lindner, Carsten Dubs, John F. Gregg, Mathias Weiler

Abstract: We study surface acoustic waves (SAWs) in yttrium iron garnet (YIG)/zinc oxide (ZnO) heterostructures, comparing the results of a computationally lightweight analytical model with time-resolved micro-focused Brillouin light scattering data. Interdigital transducers (IDTs), with operational frequencies in the gigahertz regime, were fabricated on 50 and 100nm thin films of YIG prior to sputter depos… ▽ More We study surface acoustic waves (SAWs) in yttrium iron garnet (YIG)/zinc oxide (ZnO) heterostructures, comparing the results of a computationally lightweight analytical model with time-resolved micro-focused Brillouin light scattering data. Interdigital transducers (IDTs), with operational frequencies in the gigahertz regime, were fabricated on 50 and 100nm thin films of YIG prior to sputter deposition of 830nm and 890nm films of piezoelectric ZnO. We find good agreement between our analytical model and micro-focused Brillouin light scattering data of the IDT frequency response and SAW group velocity, with clear differentiation between the Rayleigh and Sezawa-like modes. This work paves the way for the study of SAW-spin wave (SW) interactions in low SW damping YIG, with the possibility of a method for future energy-efficient SW excitation. △ Less

Submitted 5 March, 2024; originally announced March 2024.

Comments: 9 pages, 5 figures. SM 11 pages, 7 figures. Submitted to Physical Review B

Journal ref: Phys. Rev. Applied 23, 034062 (2025)

Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures

Authors: Rostyslav O. Serha, Andrey A. Voronov, David Schmoll, Roman Verba, Khrystyna O. Levchenko, Sabri Koraltan, Kristýna Davídková, Barbora Budinska, Qi Wang, Oleksandr V. Dobrovolskiy, Michal Urbánek, Morris Lindner, Timmy Reimann, Carsten Dubs, Carlos Gonzalez-Ballestero, Claas Abert, Dieter Suess, Dmytro A. Bozhko, Sebastian Knauer, Andrii V. Chumak

Abstract: Quantum magnonics investigates the quantum-mechanical properties of magnons such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolini… ▽ More Quantum magnonics investigates the quantum-mechanical properties of magnons such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 $\mathrmμ$m-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultra-low millikelvin temperatures, crucial for developing quantum magnonic devices. △ Less

Submitted 19 February, 2024; originally announced February 2024.

Journal ref: npj Spintronics 2, 29 (2024)

Nonlinear erasing of propagating spin-wave pulses in thin-film Ga:YIG

Authors: David Breitbach, Moritz Bechberger, Björn Heinz, Abbass Hamadeh, Jan Maskill, Khrystyna Levchenko, Bert Lägel, Carsten Dubs, Qi Wang, Roman Verba, Philipp Pirro

Abstract: Nonlinear phenomena are key for magnon-based information processing, but the nonlinear interaction between two spin-wave signals requires their spatio-temporal overlap which can be challenging for directional processing devices. Our study focuses on a gallium-substituted yttrium iron garnet film, which exhibits an exchange-dominated dispersion relation and thus provides a particularly broad range… ▽ More Nonlinear phenomena are key for magnon-based information processing, but the nonlinear interaction between two spin-wave signals requires their spatio-temporal overlap which can be challenging for directional processing devices. Our study focuses on a gallium-substituted yttrium iron garnet film, which exhibits an exchange-dominated dispersion relation and thus provides a particularly broad range of group velocities compared to pure YIG. Using time- and space-resolved Brillouin light scattering spectroscopy, we demonstrate the excitation of time-separated spin-wave pulses at different frequencies from the same source, where the delayed pulse catches up with the previously excited pulse and outruns it due to its higher group velocity. By varying the excitation power of the faster pulse, the outcome can be finely tuned from a linear superposition to a nonlinear interaction of both pulses, resulting in a full attenuation of the slower pulse. Therefore, our findings demonstrate the all-magnonic erasing process of a propagating magnonic signal, which enables the realization of complex temporal logic operations with potential application, e.g., in inhibitory neuromorphic functionalities. △ Less

Submitted 1 February, 2024; v1 submitted 29 November, 2023; originally announced November 2023.

Comments: 6 pages, 5 figures, revised article

Propagating spin-wave spectroscopy in nanometer-thick YIG films at millikelvin temperatures

Authors: Sebastian Knauer, Kristýna Davídková, David Schmoll, Rostyslav O. Serha, Andrey Voronov, Qi Wang, Roman Verba, Oleksandr V. Dobrovolskiy, Morris Lindner, Timmy Reimann, Carsten Dubs, Michal Urbánek, Andrii V. Chumak

Abstract: Performing propagating spin-wave spectroscopy of thin films at millikelvin temperatures is the next step towards the realisation of large-scale integrated magnonic circuits for quantum applications. Here we demonstrate spin-wave propagation in a $100\,\mathrm{nm}$-thick yttrium-iron-garnet film at the temperatures down to $45 \,\mathrm{mK}$, using stripline nanoantennas deposited on YIG surface fo… ▽ More Performing propagating spin-wave spectroscopy of thin films at millikelvin temperatures is the next step towards the realisation of large-scale integrated magnonic circuits for quantum applications. Here we demonstrate spin-wave propagation in a $100\,\mathrm{nm}$-thick yttrium-iron-garnet film at the temperatures down to $45 \,\mathrm{mK}$, using stripline nanoantennas deposited on YIG surface for the electrical excitation and detection. The clear transmission characteristics over the distance of $10\,μ\mathrm{m}$ are measured and the subtracted spin-wave group velocity and the YIG saturation magnetisation agree well with the theoretical values. We show that the gadolinium-gallium-garnet substrate influences the spin-wave propagation characteristics only for the applied magnetic fields beyond $75\,\mathrm{mT}$, originating from a GGG magnetisation up to $47 \,\mathrm{kA/m}$ at $45 \,\mathrm{mK}$. Our results show that the developed fabrication and measurement methodologies enable the realisation of integrated magnonic quantum nanotechnologies at millikelvin temperatures. △ Less

Submitted 22 January, 2023; v1 submitted 5 December, 2022; originally announced December 2022.

Comments: 6 pages, 5 figures

High wave vector non-reciprocal spin wave beams

Authors: L. Temdie, V. Castel, C. Dubs, G. Pradhan, J. Solano, H. Majjad, R. Bernard, Y. Henry, M. Bailleul, V. Vlaminck

Abstract: We report unidirectional transmission of micron-wide spin waves beams in a 55 nm thin YIG. We downscaled a chiral coupling technique implementing Ni80Fe20 nanowires arrays with different widths and lattice spacing to study the non-reciprocal transmission of exchange spin waves down to lambda = 80 nm. A full spin wave spectroscopy analysis of these high wavevector coupled-modes shows some difficult… ▽ More We report unidirectional transmission of micron-wide spin waves beams in a 55 nm thin YIG. We downscaled a chiral coupling technique implementing Ni80Fe20 nanowires arrays with different widths and lattice spacing to study the non-reciprocal transmission of exchange spin waves down to lambda = 80 nm. A full spin wave spectroscopy analysis of these high wavevector coupled-modes shows some difficulties to characterize their propagation properties, due to both the non-monotonous field dependence of the coupling efficiency, and also the inhomogeneous stray field from the nanowires. △ Less

Submitted 12 January, 2023; v1 submitted 10 November, 2022; originally announced November 2022.

Comments: submitted to AIP advances as MMM proceeding article

Stimulated amplification of propagating spin waves

Authors: David Breitbach, Michael Schneider, Björn Heinz, Felix Kohl, Jan Maskill, Laura Scheuer, Rostyslav O. Serha, Thomas Brächer, Bert Lägel, Carsten Dubs, Vasil S. Tiberkevich, Andrei N. Slavin, Alexander A. Serga, Burkard Hillebrands, Andrii V. Chumak, Philipp Pirro

Abstract: Spin-wave amplification techniques are key to the realization of magnon-based computing concepts. We introduce a novel mechanism to amplify spin waves in magnonic nanostructures. Using the technique of rapid cooling, we create a non-equilibrium state in excess of high-energy magnons and demonstrate the stimulated amplification of an externally seeded, propagating spin wave. Using an extended kinet… ▽ More Spin-wave amplification techniques are key to the realization of magnon-based computing concepts. We introduce a novel mechanism to amplify spin waves in magnonic nanostructures. Using the technique of rapid cooling, we create a non-equilibrium state in excess of high-energy magnons and demonstrate the stimulated amplification of an externally seeded, propagating spin wave. Using an extended kinetic model, we qualitatively show that the amplification is mediated by an effective energy flux of high energy magnons into the low energy propagating mode, driven by a non-equilibrium magnon distribution. △ Less

Submitted 1 November, 2023; v1 submitted 24 August, 2022; originally announced August 2022.

Journal ref: Physical Review Letters 131, 156701 (2023)

Thermal spin current generation in the multifunctional ferrimagnet Ga$_{0.6}$Fe$_{1.4}$O$_{3}$

Authors: Alberto Anadón, Elodie Martin, Suvidyakumar Homkar, Benjamin Meunier, Maxime Verges, Heloise Damas, Junior Alegre, Christophe Lefevre, Francois Roulland, Carsten Dubs, Morris Lindner, Ludovic Pasquier, Olivier Copie, Karine Dumesnil, Rafael Ramos, Daniele Preziosi, Sébastien Petit-Watelot, Nathalie Viart, Juan-Carlos Rojas-Sánchez

Abstract: In recent years, multifunctional materials have attracted increasing interest for magnetic memories and energy harvesting applications. Magnetic insulating materials are of special interest for this purpose, since they allow the design of more efficient devices due to the lower Joule heat losses. In this context, Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) is a good candidate for spintronics applications, sin… ▽ More In recent years, multifunctional materials have attracted increasing interest for magnetic memories and energy harvesting applications. Magnetic insulating materials are of special interest for this purpose, since they allow the design of more efficient devices due to the lower Joule heat losses. In this context, Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) is a good candidate for spintronics applications, since it can exhibit multiferroicity and presents a spin Hall magnetoresistance similar to the one observed in a yttrium iron garnet (YIG)/Pt bilayer. Here, we explore GFO utilizing thermo-spin measurements in an on-chip approach. By carefully considering the geometry of our thermo-spin devices we are able to quantify the spin Seebeck effect and the spin current generation in a GFO/Pt bilayer, obtaining a value comparable to that of YIG/Pt. This further confirms the promises of an efficient spin current generation with the possibility of an electric-field manipulation of the magnetic properties of the system in an insulating ferrimagnetic material. △ Less

Submitted 3 July, 2022; v1 submitted 27 June, 2022; originally announced June 2022.

Multi-band Bose-Einstein condensate at four-particle scattering resonance

Authors: Joe Bailey, Pavlo Sukhachov, Korbinian Baumgaertl, Simone Finizio, Sebastian Wintz, Carsten Dubs, Joerg Raabe, Dirk Grundler, Alexander Balatsky, Gabriel Aeppli

Abstract: Superfluidity and superconductivity are macroscopic manifestations of quantum mechanics, which have fascinated scientists since their discoveries roughly a century ago. Ever since the initial theories of such quantum fluids were formulated, there has been speculation as to the possibility of multi-component quantum order. A particularly simple multi-component condensate is built from particles occ… ▽ More Superfluidity and superconductivity are macroscopic manifestations of quantum mechanics, which have fascinated scientists since their discoveries roughly a century ago. Ever since the initial theories of such quantum fluids were formulated, there has been speculation as to the possibility of multi-component quantum order. A particularly simple multi-component condensate is built from particles occupying different quantum states, or bands, prior to condensation. The particles in one or both bands may undergo condensation, as seen for certain solids and anticipated for certain cold atom systems. For bulk solids, the different bands always order simultaneously, with conventional pairing characterized by complex order parameters describing the condensates in each band. Another type of condensate, notably occurring at room temperature, has been identified for magnons, the magnetic analogue of lattice vibrations, injected by microwaves into yttrium iron garnet. Here we show that magnon quantization for thin samples results in a new multi-band magnon condensate. We establish a phase diagram, as a function of microwave drive power and frequency relative to the magnon bands, revealing both single and multi-band condensation. The most stable multi-band condensate is found in a narrow regime favoured on account of a resonance in the scattering between two bands. Our discovery introduces a flexible non-equilibrium platform operating at room temperature for a well-characterised material, exploiting a Feshbach-like resonance, for examining multi-band phenomena. It points to qualitatively new ways to engineer and control condensates and superconducting states in multiband systems and potential devices containing multiple interacting condensates. △ Less

Submitted 26 January, 2022; originally announced January 2022.

Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG

Authors: T. Böttcher, M. Ruhwedel, K. O. Levchenko, Q. Wang, H. L. Chumak, M. A. Popov, I. V. Zavislyak, C. Dubs, O. Surzhenko, B. Hillebrands, A. V. Chumak, P. Pirro

Abstract: Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant $λ_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering (BLS) spectroscopy, we direct… ▽ More Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant $λ_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering (BLS) spectroscopy, we directly measure $λ_\mathrm{ex}$ in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers $k > 4$ rad/$μ$m, and the ratio between the velocities reaches a constant value of around 3.4 for all $k > 20$ rad/$μ$m. As revealed by vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR) spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping ($α< 10^{-3}$), a decreased saturation magnetization $μ_0 M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy of about $μ_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects. △ Less

Submitted 21 December, 2021; originally announced December 2021.

Comments: 5 pages, 3 figures, 39 references, Supplemental material

Roadmap on Spin-Wave Computing

Authors: A. V. Chumak, P. Kabos, M. Wu, C. Abert, C. Adelmann, A. Adeyeye, J. Åkerman, F. G. Aliev, A. Anane, A. Awad, C. H. Back, A. Barman, G. E. W. Bauer, M. Becherer, E. N. Beginin, V. A. S. V. Bittencourt, Y. M. Blanter, P. Bortolotti, I. Boventer, D. A. Bozhko, S. A. Bunyaev, J. J. Carmiggelt, R. R. Cheenikundil, F. Ciubotaru, S. Cotofana , et al. (91 additional authors not shown)

Abstract: Magnonics is a field of science that addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operations in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the… ▽ More Magnonics is a field of science that addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operations in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors that covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with Boolean digital data, unconventional approaches like neuromorphic computing, and the progress towards magnon-based quantum computing. The article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of the current challenges and the outlook of the further development of the research directions. △ Less

Submitted 30 October, 2021; originally announced November 2021.

Comments: 74 pages, 57 figures, 500 references

Journal ref: IEEE Transactions on Magnetics 58, 0800172 (2022)

Electrical spectroscopy of the spin-wave dispersion and bistability in gallium-doped yttrium iron garnet

Authors: Joris J. Carmiggelt, Olaf C. Dreijer, Carsten Dubs, Oleksii Surzhenko, Toeno van der Sar

Abstract: Yttrium iron garnet (YIG) is a magnetic insulator with record-low damping, allowing spin-wave transport over macroscopic distances. Doping YIG with gallium ions greatly reduces the demagnetizing field and introduces a perpendicular magnetic anisotropy, which leads to an isotropic spin-wave dispersion that facilitates spin-wave optics and spin-wave steering. Here, we characterize the dispersion of… ▽ More Yttrium iron garnet (YIG) is a magnetic insulator with record-low damping, allowing spin-wave transport over macroscopic distances. Doping YIG with gallium ions greatly reduces the demagnetizing field and introduces a perpendicular magnetic anisotropy, which leads to an isotropic spin-wave dispersion that facilitates spin-wave optics and spin-wave steering. Here, we characterize the dispersion of a gallium-doped YIG (Ga:YIG) thin film using electrical spectroscopy. We determine the magnetic anisotropy parameters from the ferromagnetic resonance frequency and use propagating spin wave spectroscopy in the Damon-Eshbach configuration to detect the small spin-wave magnetic fields of this ultrathin weak magnet over a wide range of wavevectors, enabling the extraction of the exchange constant $α=1.3(2)\times10^{-12}$ J/m. The frequencies of the spin waves shift with increasing drive power, which eventually leads to the foldover of the spin-wave modes. Our results shed light on isotropic spin-wave transport in Ga:YIG and highlight the potential of electrical spectroscopy to map out the dispersion and bistability of propagating spin waves in magnets with a low saturation magnetization. △ Less

Submitted 10 September, 2021; originally announced September 2021.

Comments: 28 pages, 11 figures

Journal ref: Appl. Phys. Lett. 119, 202403 (2021)

Spin-wave dispersion measurement by variable-gap propagating spin-wave spectroscopy

Authors: Marek Vaňatka, Krzysztof Szulc, Ondřej Wojewoda, Carsten Dubs, Andrii Chumak, Maciej Krawczyk, Oleksandr V. Dobrovolskiy, Jarosław W. Kłos, Michal Urbánek

Abstract: Magnonics is seen nowadays as a candidate technology for energy-efficient data processing in classical and quantum systems. Pronounced nonlinearity, anisotropy of dispersion relations and phase degree of freedom of spin waves require advanced methodology for probing spin waves at room as well as at mK temperatures. Yet, the use of the established optical techniques like Brillouin light scattering… ▽ More Magnonics is seen nowadays as a candidate technology for energy-efficient data processing in classical and quantum systems. Pronounced nonlinearity, anisotropy of dispersion relations and phase degree of freedom of spin waves require advanced methodology for probing spin waves at room as well as at mK temperatures. Yet, the use of the established optical techniques like Brillouin light scattering (BLS) or magneto optical Kerr effect (MOKE) at ultra-low temperatures is forbiddingly complicated. By contrast, microwave spectroscopy can be used at all temperatures but is usually lacking spatial and wavenumber resolution. Here, we develop a variable-gap propagating spin-wave spectroscopy (VG-PSWS) method for the deduction of the dispersion relation of spin waves in wide frequency and wavenumber range. The method is based on the phase-resolved analysis of the spin-wave transmission between two antennas with variable spacing, in conjunction with theoretical data treatment. We validate the method for the in-plane magnetized CoFeB and YIG thin films in $k\perp B$ and $k\parallel B$ geometries by deducing the full set of material and spin-wave parameters, including spin-wave dispersion, hybridization of the fundamental mode with the higher-order perpendicular standing spin-wave modes and surface spin pinning. The compatibility of microwaves with low temperatures makes this approach attractive for cryogenic magnonics at the nanoscale. △ Less

Submitted 20 July, 2021; originally announced July 2021.

Comments: 9 pages, 5 figures

Stabilization of a nonlinear bullet coexisting with a Bose-Einstein condensate in a rapidly cooled magnonic system driven by a spin-orbit torque

Authors: Michael Schneider, David Breitbach, Rostyslav O. Serha, Qi Wang, Morteza Mohseni, Alexander A. Serga, Andrei N. Slavin, Vasyl S. Tiberkevich, Björn Heinz, Thomas Brächer, Bert Lägel, Carsten Dubs, Sebastian Knauer, Oleksandr V. Dobrovolskiy, Philipp Pirro, Burkard Hillebrands, Andrii V. Chumak

Abstract: We have recently shown that injection of magnons into a magnetic dielectric via the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal subjected to the action of short (0.1 $μ$s) current pulses allows for control of a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the process of rapid cooling (RC), when the electric current heating the sample is abruptly term… ▽ More We have recently shown that injection of magnons into a magnetic dielectric via the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal subjected to the action of short (0.1 $μ$s) current pulses allows for control of a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the process of rapid cooling (RC), when the electric current heating the sample is abruptly terminated. In the present study, we show that the application of a longer (1.0 $μ$s) electric current pulse triggers the formation of a nonlinear localized magnonic bullet below the linear magnon spectrum. After pulse termination, the magnon BEC, as before, is formed at the bottom of the linear spectrum, but the nonlinear bullet continues to exist, stabilized for additional 30 ns by the same process of RC-induced magnon condensation. Our results suggest that a stimulated condensation of excess magnons to all highly populated magnonic states occurs. △ Less

Submitted 28 June, 2021; originally announced June 2021.

Journal ref: Physical Review B 104, L140405 (2021)

Parametric generation of spin waves in nano-scaled magnonic conduits

Authors: Björn Heinz, Morteza Mohseni, Akira Lentfert, Roman Verba, Michael Schneider, Bert Lägel, Khrystyna Levchenko, Thomas Brächer, Carsten Dubs, Andrii V. Chumak, Philipp Pirro

Abstract: The research feld of magnonics proposes a low-energy wave-logic computation technology based on spin waves to complement the established CMOS technology and provide a basis for emerging unconventional computation architectures. However, magnetic damping is a limiting factor for all-magnonic logic circuits and multi-device networks, ultimately rendering mechanisms to effciently manipulate and ampli… ▽ More The research feld of magnonics proposes a low-energy wave-logic computation technology based on spin waves to complement the established CMOS technology and provide a basis for emerging unconventional computation architectures. However, magnetic damping is a limiting factor for all-magnonic logic circuits and multi-device networks, ultimately rendering mechanisms to effciently manipulate and amplify spin waves a necessity. In this regard, parallel pumping is a versatile tool since it allows to selectively generate and amplify spin waves. While extensively studied in microscopic systems, nano-scaled systems are lacking investigation to assess the feasibility and potential future use of parallel pumping in magnonics. Here, we investigate a longitudinally magnetized 100 nm-wide magnonic nano-conduit using space and time-resolved micro-focused Brillouin-light-scattering spectroscopy. Employing parallel pumping to generate spin waves, we observe that the non-resonant excitation of dipolar spin waves is favored over the resonant excitation of short wavelength exchange spin waves. In addition, we utilize this technique to access the effective spin-wave relaxation time of an individual nano-conduit, observing a large relaxation time up to (115.0 +- 7.6) ns. Despite the significant decrease of the pumping effciency in the investigated nano-conduit, a reasonably small threshold is found rendering parallel pumping feasible on the nano-scale. △ Less

Submitted 15 January, 2022; v1 submitted 20 June, 2021; originally announced June 2021.

Control of the Bose-Einstein Condensation of Magnons by the Spin-Hall Effect

Authors: Michael Schneider, David Breitbach, Rostyslav O. Serha, Qi Wang, Alexander A. Serga, Andrei N. Slavin, Vasyl S. Tiberkevich, Björn Heinz, Bert Lägel, Thomas Brächer, Carsten Dubs, Sebastian Knauer, Oleksandr V. Dobrovolskiy, Philipp Pirro, Burkard Hillebrands, Andrii V. Chumak

Abstract: Previously, it has been shown that rapid cooling of yttrium-iron-garnet (YIG)/platinum (Pt) nano structures, preheated by an electric current sent through the Pt layer, leads to overpopulation of a magnon gas and to subsequent formation of a Bose-Einstein condensate (BEC) of magnons. The spin Hall effect (SHE), which creates a spin-polarized current in the Pt layer, can inject or annihilate magnon… ▽ More Previously, it has been shown that rapid cooling of yttrium-iron-garnet (YIG)/platinum (Pt) nano structures, preheated by an electric current sent through the Pt layer, leads to overpopulation of a magnon gas and to subsequent formation of a Bose-Einstein condensate (BEC) of magnons. The spin Hall effect (SHE), which creates a spin-polarized current in the Pt layer, can inject or annihilate magnons depending on the electric current and applied field orientations. Here we demonstrate that the injection or annihilation of magnons via the SHE can prevent or promote the formation of a rapid cooling induced magnon BEC. Depending on the current polarity, a change in the BEC threshold of -8% and +6% was detected. These findings demonstrate a new method to control macroscopic quantum states, paving the way for their application in spintronic devices. △ Less

Submitted 22 September, 2021; v1 submitted 26 February, 2021; originally announced February 2021.

Journal ref: Physical Review Letters 127, 237203 (2021)

Long-range spin-wave propagation in transversely magnetized nano-scaled conduits

Authors: Björn Heinz, Qi Wang, Michael Schneider, Elisabeth Weiß, Akira Lentfert, Bert Lägel, Thomas Brächer, Carsten Dubs, Oleksandr V. Dobrovolskiy, Philipp Pirro, Andrii V. Chumak

Abstract: Magnonics attracts increasing attention in the view of novel low-energy computation technologies based on spin waves. Recently, spin-wave propagation in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated, proving the fundamental feasibility of magnonics at the sub-100 nm scale. Transversely magnetized nano-conduits, which are of great interest in this regard as they offer a… ▽ More Magnonics attracts increasing attention in the view of novel low-energy computation technologies based on spin waves. Recently, spin-wave propagation in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated, proving the fundamental feasibility of magnonics at the sub-100 nm scale. Transversely magnetized nano-conduits, which are of great interest in this regard as they offer a large group velocity and a potentially chirality-based protected transport of energy, have not yet been investigated due to their complex internal magnetic field distribution. Here, we present a study of propagating spin waves in a transversely magnetized nanoscopic yttrium iron garnet conduit of 50 nm width. Space and time-resolved micro-focused Brillouin-light-scattering spectroscopy is employed to measure the spin-wave group velocity and decay length. A long-range spin-wave propagation is observed with a decay length of up to (8.0+-1.5) μm and a large spin-wave lifetime of up to (44.7+-9.1) ns. The results are supported with micromagnetic simulations, revealing a single-mode dispersion relation in contrast to the common formation of localized edge modes for microscopic systems. Furthermore, a frequency non-reciprocity for counter-propagating spin waves is observed in the simulations and the experiment, caused by the trapezoidal cross-section of the structure. The revealed long-distance spin-wave propagation on the nanoscale is particularly interesting for an application in spin-wave devices, allowing for long-distance transport of information in magnonic circuits, as well as novel low-energy device architectures. △ Less

Submitted 25 January, 2021; originally announced January 2021.

Controlling the nonlinear relaxation of quantized propagating magnons in nanodevices

Authors: M. Mohseni, Q. Wang, B. Heinz, M. Kewenig, M. Schneider, F. Kohl, B. Lägel, C. Dubs, A. V. Chumak, P. Pirro

Abstract: Relaxation of linear magnetization dynamics is well described by the viscous Gilbert damping processes. However, for strong excitations, nonlinear damping processes such as the decay via magnon-magnon interactions emerge and trigger additional relaxation channels. Here, we use space- and time-resolved microfocused Brillouin light scattering spectroscopy and micromagnetic simulations to investigate… ▽ More Relaxation of linear magnetization dynamics is well described by the viscous Gilbert damping processes. However, for strong excitations, nonlinear damping processes such as the decay via magnon-magnon interactions emerge and trigger additional relaxation channels. Here, we use space- and time-resolved microfocused Brillouin light scattering spectroscopy and micromagnetic simulations to investigate the nonlinear relaxation of strongly driven propagating spin waves in yttrium iron garnet nanoconduits. We show that the nonlinear magnon relaxation in this highly quantized system possesses intermodal features, i.e., magnons scatter to higher-order quantized modes through a cascade of scattering events. We further show how to control such intermodal dissipation processes by quantization of the magnon band in single-mode devices, where this phenomenon approaches its fundamental limit. Our study extends the knowledge about nonlinear propagating spin waves in nanostructures which is essential for the construction of advanced spin-wave elements as well as the realization of Bose-Einstein condensates in scaled systems. △ Less

Submitted 7 March, 2021; v1 submitted 5 June, 2020; originally announced June 2020.

Comments: 8 pages, 4 figures

Journal ref: Phys. Rev. Lett. 126, 097202 (2021)

Local spin Seebeck imaging with scanning thermal probe

Authors: Alessandro Sola, Vittorio Basso, Massimo Pasquale, Carsten Dubs, Craig Barton, Olga Kazakowa

Abstract: In this work we present the results of an experiment to locally resolve the spin Seebeck effect in a high-quality Pt/YIG sample. We achieve this by employing a locally heated scanning thermal probe to generate a highly local non-equilibrium spin current. To support our experimental results, we also present a model based on the non-equilibrium thermodynamic approach which is in a good agreement wit… ▽ More In this work we present the results of an experiment to locally resolve the spin Seebeck effect in a high-quality Pt/YIG sample. We achieve this by employing a locally heated scanning thermal probe to generate a highly local non-equilibrium spin current. To support our experimental results, we also present a model based on the non-equilibrium thermodynamic approach which is in a good agreement with experimental findings. To further corroborate our results, we index the locally resolved spin Seebeck effect with that of the local magnetisation texture by MFM and correlate corresponding regions. We hypothesise that this technique allows imaging of magnetisation textures within the magnon diffusion length and hence characterisation of spin caloritronic materials at the nanoscale. △ Less

Submitted 18 May, 2020; originally announced May 2020.

Journal ref: Phys. Rev. Applied 14, 034056 (2020)

Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy

Authors: Carsten Dubs, Oleksii Surzhenko, Ronny Thomas, Julia Osten, Tobias Schneider, Kilian Lenz, Jörg Grenzer, René Hübner, Elke Wendler

Abstract: The field of magnon spintronics is experiencing an increasing interest in the development of solutions for spin-wave-based data transport and processing technologies that are complementary or alternative to modern CMOS architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the gold standard for insulator-based spintronics to date, but a potential process technology that can delive… ▽ More The field of magnon spintronics is experiencing an increasing interest in the development of solutions for spin-wave-based data transport and processing technologies that are complementary or alternative to modern CMOS architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the gold standard for insulator-based spintronics to date, but a potential process technology that can deliver perfect, homogeneous large-diameter films is still lacking. We report that liquid phase epitaxy (LPE) enables the deposition of nanometer-thin YIG films with low ferromagnetic resonance losses and consistently high magnetic quality down to a thickness of 20 nm. The obtained epitaxial films are characterized by an ideal stoichiometry and perfect film lattices, which show neither significant compositional strain nor geometric mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is similar to that of single crystalline bulk YIG. We found, that the Gilbert damping coefficient alpha is independent of the film thickness and close to 1 x 10-4, and that together with an inhomogeneous peak-to-peak linewidth broadening of delta H0|| = 0.4 G, these values are among the lowest ever reported for YIG films with a thickness smaller than 40 nm. These results suggest, that nanometer-thin LPE films can be used to fabricate nano- and micro-scaled circuits with the required quality for magnonic devices. The LPE technique is easily scalable to YIG sample diameters of several inches. △ Less

Submitted 21 November, 2019; originally announced November 2019.

Journal ref: Phys. Rev. Materials 4, 024416 (2020)

Parametric generation of propagating spin-waves in ultra thin yttrium iron garnet waveguides

Authors: M. Mohseni, M. Kewenig, R. Verba, Q. Wang, M. Schneider, B. Heinz, F. Kohl, C. Dubs, B. Lägel, A. A. Serga, B. Hillebrands, A. V. Chumak, P. Pirro

Abstract: We present the experimental demonstration of the parallel parametric generation of spin-waves in a microscaled yttrium iron garnet waveguide with nanoscale thickness. Using Brillouin light scattering microscopy, we observe the excitation of the first and second waveguide modes generated by a stripline microwave pumping source. Micromagnetic simulations reveal the wave vector of the parametrically… ▽ More We present the experimental demonstration of the parallel parametric generation of spin-waves in a microscaled yttrium iron garnet waveguide with nanoscale thickness. Using Brillouin light scattering microscopy, we observe the excitation of the first and second waveguide modes generated by a stripline microwave pumping source. Micromagnetic simulations reveal the wave vector of the parametrically generated spin-waves. Based on analytical calculations, which are in excellent agreement with our experiments and simulations, we prove that the spin-wave radiation losses are the determinative term of the parametric instability threshold in this miniaturized system. The used method enables the direct excitation and amplification of nanometer spin-waves dominated by exchange interactions. Our results pave the way for integrated magnonics based on insulating nano-magnets. △ Less

Submitted 14 February, 2020; v1 submitted 12 November, 2019; originally announced November 2019.

Comments: 10 pages, 3 figures

Journal ref: Physica Status Solidi RRL 14, 2000011 (2020)

Propagation of spin-waves packets in individual nano-sized yttrium iron garnet magnonic conduits

Authors: Björn Heinz, Thomas Brächer, Michael Schneider, Qi Wang, Bert Lägel, Anna M. Friedel, David Breitbach, Steffen Steinert, Thomas Meyer, Martin Kewenig, Carsten Dubs, Philipp Pirro, Andrii V. Chumak

Abstract: Modern-days CMOS-based computation technology is reaching its fundamental limitations. The emerging field of magnonics, which utilizes spin waves for data transport and processing, proposes a promising path to overcome these limitations. Different devices have been demonstrated recently on the macro- and microscale, but the feasibility of the magnonics approach essentially relies on the scalabilit… ▽ More Modern-days CMOS-based computation technology is reaching its fundamental limitations. The emerging field of magnonics, which utilizes spin waves for data transport and processing, proposes a promising path to overcome these limitations. Different devices have been demonstrated recently on the macro- and microscale, but the feasibility of the magnonics approach essentially relies on the scalability of the structure feature size down to an extent of a few 10 nm, which are typical sizes for the established CMOS technology. Here, we present a study of propagating spin-wave packets in individual yttrium iron garnet (YIG) conduits with lateral dimensions down to 50 nm. Space and time resolved micro-focused Brillouin-Light-Scattering (BLS) spectroscopy is used to characterize the YIG nanostructures and measure the spin-wave decay length and group velocity directly. The revealed magnon transport at the scale comparable to the scale of CMOS proves the general feasibility of a magnon-based data processing. △ Less

Submitted 4 February, 2020; v1 submitted 19 October, 2019; originally announced October 2019.

Journal ref: Nano Lett. 2020, 20, 6, 4220-4227

A magnonic directional coupler for integrated magnonic half-adders

Authors: Q. Wang, M. Kewenig, M. Schneider, R. Verba, F. Kohl, B. Heinz, M. Geilen, M. Mohseni, B. Lägel, F. Ciubotaru, C. Adelmann, C. Dubs, S. D. Cotofana, O. V. Dobrovolskiy, T. Brächer, P. Pirro, A. V. Chumak

Abstract: Magnons, the quanta of spin waves, could be used to encode information in beyond-Moore computing applications, and magnonic device components, including logic gates, transistors, and units for non-Boolean computing, have already been developed. Magnonic directional couplers, which can function as circuit building blocks, have also been explored, but have been impractical because of their millimetr… ▽ More Magnons, the quanta of spin waves, could be used to encode information in beyond-Moore computing applications, and magnonic device components, including logic gates, transistors, and units for non-Boolean computing, have already been developed. Magnonic directional couplers, which can function as circuit building blocks, have also been explored, but have been impractical because of their millimetre dimensions and multi-mode spectra. Here, we report a magnonic directional coupler based on yttrium iron garnet single-mode waveguides of 350 nm width. We use the amplitude of a spin-wave to encode information and to guide it to one of the two outputs of the coupler depending on the signal magnitude, frequency, and the applied magnetic field. Using micromagnetic simulations, we also propose an integrated magnonic half-adder that consists of two directional couplers and processes all information within the magnon domain with aJ energy consumption. △ Less

Submitted 7 September, 2021; v1 submitted 29 May, 2019; originally announced May 2019.

Comments: 26 pages, 10 figures. arXiv admin note: text overlap with arXiv:1902.02855

Journal ref: Nature Electronics 2020

Nanoscale X-Ray Imaging of Spin Dynamics in Yttrium Iron Garnet

Authors: J. Förster, S. Wintz, J. Bailey, S. Finizio, E. Josten, D. Meertens, C. Dubs, D. A. Bozhko, H. Stoll, G. Dieterle, N. Träger, J. Raabe, A. N. Slavin, M. Weigand, J. Gräfe, G. Schütz

Abstract: Time-resolved scanning transmission x-ray microscopy (TR-STXM) has been used for the direct imaging of spin wave dynamics in thin film yttrium iron garnet (YIG) with spatial resolution in the sub 100 nm range. Application of this x-ray transmission technique to single crystalline garnet films was achieved by extracting a lamella (13x5x0.185 $\mathrm{μm^3}$) of liquid phase epitaxy grown YIG thin f… ▽ More Time-resolved scanning transmission x-ray microscopy (TR-STXM) has been used for the direct imaging of spin wave dynamics in thin film yttrium iron garnet (YIG) with spatial resolution in the sub 100 nm range. Application of this x-ray transmission technique to single crystalline garnet films was achieved by extracting a lamella (13x5x0.185 $\mathrm{μm^3}$) of liquid phase epitaxy grown YIG thin film out of a gadolinium gallium garnet substrate. Spin waves in the sample were measured along the Damon-Eshbach and backward volume directions of propagation at gigahertz frequencies and with wavelengths in a range between 100~nm and 10~$\mathrmμ$m. The results were compared to theoretical models. Here, the widely used approximate dispersion equation for dipole-exchange spin waves proved to be insufficient for describing the observed Damon-Eshbach type modes. For achieving an accurate description, we made use of the full analytical theory taking mode-hybridization effects into account. △ Less

Submitted 1 March, 2019; originally announced March 2019.

Interplay of magnetization dynamics with microwave waveguide at cryogenic temperatures

Authors: I. A. Golovchanskiy, N. N. Abramov, M. Pfirrmann, T. Piskor, J. N. Voss, D. S. Baranov, R. A. Hovhannisyan, V. S. Stolyarov, C. Dubs, A. A. Golubov, V. V. Ryazanov, A. V. Ustinov, M. Weides

Abstract: In this work, magnetization dynamics is studied at low temperatures in a hybrid system that consists of thin epitaxial magnetic film coupled with superconducting planar microwave waveguide. The resonance spectrum was observed in a wide magnetic field range, including low fields below the saturation magnetization and both polarities. Analysis of the spectrum via a developed fitting routine allowed… ▽ More In this work, magnetization dynamics is studied at low temperatures in a hybrid system that consists of thin epitaxial magnetic film coupled with superconducting planar microwave waveguide. The resonance spectrum was observed in a wide magnetic field range, including low fields below the saturation magnetization and both polarities. Analysis of the spectrum via a developed fitting routine allowed to derive all magnetic parameters of the film at cryogenic temperatures, to detect waveguide-induced uniaxial magnetic anisotropies of the first and the second order, and to uncover a minor misalignment of magnetic field. A substantial influence of the superconducting critical state on resonance spectrum is observed and discussed. △ Less

Submitted 28 March, 2019; v1 submitted 20 February, 2019; originally announced February 2019.

Comments: 10 pages, 6 figures

Journal ref: Physical Review APPLIED 11, 044076 (2019)

Experimental proof of the reciprocal relation between spin Peltier and spin Seebeck effects in a bulk YIG/Pt bilayer

Authors: Alessandro Sola, Vittorio Basso, Michaela Kuepferling, Carsten Dubs, Massimo Pasquale

Abstract: We verify for the first time the reciprocal relation between the spin Peltier and spin Seebeck effects in a bulk YIG/Pt bilayer. Both experiments are performed on the same YIG/Pt device by a setup able to accurately determine heat currents and to separate the spin Peltier heat from the Joule heat background. The sample-specific value for the characteristics of both effects measured on the present… ▽ More We verify for the first time the reciprocal relation between the spin Peltier and spin Seebeck effects in a bulk YIG/Pt bilayer. Both experiments are performed on the same YIG/Pt device by a setup able to accurately determine heat currents and to separate the spin Peltier heat from the Joule heat background. The sample-specific value for the characteristics of both effects measured on the present YIG/Pt bilayer is $(6.2 \pm 0.4)\times 10^{-3} \,\, \mbox{KA$^{-1}$}$. In the paper we also discuss the relation of both effects with the intrinsic and extrinsic parameters of YIG and Pt and we envisage possible strategies to optimize spin Peltier refrigeration. △ Less

Submitted 13 November, 2018; originally announced November 2018.

Comments: 11 pages, 3 figures

Journal ref: Scientific Reports (2019) 9:2047

Optimization of Multi-Frequency Magnonic Waveguides with Enhanced Group Velocities by Exchange Coupled Ferrimagnet/Ferromagnet Bilayers

Authors: Kyongmo An, Vinayak Bhat, Michal Mruczkiewicz, Carsten Dubs, Dirk Grundler

Abstract: We report broadband spectroscopy and numerical analysis by which we explore propagating spin waves in a magnetic bilayer consisting of a 23 nm thick permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer, we observe a characteristic mode that exhibits a considerably larger group velocity at small in-plane magnetic field than both the magnetostatic and perpendicular standing s… ▽ More We report broadband spectroscopy and numerical analysis by which we explore propagating spin waves in a magnetic bilayer consisting of a 23 nm thick permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer, we observe a characteristic mode that exhibits a considerably larger group velocity at small in-plane magnetic field than both the magnetostatic and perpendicular standing spin waves. Using the finite element method, we confirm the observations by simulating the mode profiles and dispersion relations. They illustrate the hybridization of spin wave modes due to exchange coupling at the interface. The high-speed propagating mode found in the bilayer can be utilized to configure multi-frequency spin wave channels enhancing the performance of spin wave based logic devices. △ Less

Submitted 12 March, 2019; v1 submitted 27 July, 2018; originally announced July 2018.

Journal ref: Phys. Rev. Applied 11, 034065 (2019)

Spin pinning and spin-wave dispersion in nanoscopic ferromagnetic waveguides

Authors: Q. Wang, B. Heinz, R. Verba, M. Kewenig, P. Pirro, M. Schneider, T. Meyer, B. Lägel, C. Dubs, T. Brächer, A. V. Chumak

Abstract: Spin waves are investigated in Yttrium Iron Garnet (YIG) waveguides with a thickness of 39 nm and widths ranging down to 50 nm, i.e., with aspect ratios thickness over width approaching unity, using Brillouin Light Scattering spectroscopy. The experimental results are verified by a semi-analytical theory and micromagnetic simulations. A critical width is found, below which the exchange interaction… ▽ More Spin waves are investigated in Yttrium Iron Garnet (YIG) waveguides with a thickness of 39 nm and widths ranging down to 50 nm, i.e., with aspect ratios thickness over width approaching unity, using Brillouin Light Scattering spectroscopy. The experimental results are verified by a semi-analytical theory and micromagnetic simulations. A critical width is found, below which the exchange interaction suppresses the dipolar pinning phenomenon. This changes the quantization criterion for the spin-wave eigenmodes and results in a pronounced modification of the spin-wave characteristics. The presented semi-analytical theory allows for the calculation of spin-wave mode profiles and dispersion relations in nano-structures. △ Less

Submitted 29 May, 2019; v1 submitted 3 July, 2018; originally announced July 2018.

Journal ref: Phys. Rev. Lett. 122, 247202 (2019)

The Final Chapter In The Saga Of YIG

Authors: A. J. Princep, R. A. Ewings, S. Ward, S. Tóth, C. Dubs, D. Prabhakaran, A. T. Boothroyd

Abstract: The magnetic insulator Yttrium Iron Garnet can be grown with exceptional quality, has a ferrimagnetic transition temperature of nearly 600 K, and is used in microwave and spintronic devices that can operate at room temperature. The most accurate prior measurements of the magnon spectrum date back nearly 40 years, but cover only 3 of the lowest energy modes out of 20 distinct magnon branches. Here… ▽ More The magnetic insulator Yttrium Iron Garnet can be grown with exceptional quality, has a ferrimagnetic transition temperature of nearly 600 K, and is used in microwave and spintronic devices that can operate at room temperature. The most accurate prior measurements of the magnon spectrum date back nearly 40 years, but cover only 3 of the lowest energy modes out of 20 distinct magnon branches. Here we have used time-of-flight inelastic neutron scattering to measure the full magnon spectrum throughout the Brillouin zone. We find that the existing model of the excitation spectrum, well known from an earlier work titled "The Saga of YIG", fails to describe the optical magnon modes. Using a very general spin Hamiltonian, we show that the magnetic interactions are both longer-ranged and more complex than was previously understood. The results provide the basis for accurate microscopic models of the finite temperature magnetic properties of Yttrium Iron Garnet, necessary for next-generation electronic devices. △ Less

Submitted 18 May, 2017; originally announced May 2017.

Comments: 10 pages, 3 figures, 4 supplementary figures, 1 table, 1 supplementary table

Journal ref: npj Quantum Materials, volume 2, Article number: 63 (2017)

Temperature dependent magnetic damping of yttrium iron garnet spheres

Authors: Hannes Maier-Flaig, Stefan Klingler, Carsten Dubs, Oleksii Surzhenko, Rudolf Gross, Mathias Weiler, Hans Huebl, Sebastian T. B. Goennenwein

Abstract: We investigate the temperature dependent microwave absorption spectrum of an yttrium iron garnet sphere as a function of temperature (5 K to 300 K) and frequency (3 GHz to 43.5 GHz). At temperatures above 100 K, the magnetic resonance linewidth increases linearly with temperature and shows a Gilbert-like linear frequency dependence. At lower temperatures, the temperature dependence of the resonanc… ▽ More We investigate the temperature dependent microwave absorption spectrum of an yttrium iron garnet sphere as a function of temperature (5 K to 300 K) and frequency (3 GHz to 43.5 GHz). At temperatures above 100 K, the magnetic resonance linewidth increases linearly with temperature and shows a Gilbert-like linear frequency dependence. At lower temperatures, the temperature dependence of the resonance linewidth at constant external magnetic fields exhibits a characteristic peak which coincides with a non-Gilbert-like frequency dependence. The complete temperature and frequency evolution of the linewidth can be modeled by the phenomenology of slowly relaxing rare-earth impurities and either the Kasuya-LeCraw mechanism or the scattering with optical magnons. Furthermore, we extract the temperature dependence of the saturation magnetization, the magnetic anisotropy and the g-factor. △ Less

Submitted 2 June, 2017; v1 submitted 28 March, 2017; originally announced March 2017.

Journal ref: Phys. Rev. B 95, 214423 (2017)

Bose-Einstein Condensation of Quasi-Particles by Rapid Cooling

Authors: M. Schneider, T. Brächer, D. Breitbach, V. Lauer, P. Pirro, D. A. Bozhko, A. A. Serga, H. Yu. Musiienko-Shmarova, B. Heinz, Q. Wang, T. Meyer, F. Heussner, S. Keller, E. Th. Papaioannou, B. Lägel, T. Löber, V. S. Tiberkevich, A. N. Slavin, C. Dubs, B. Hillebrands, A. V. Chumak

Abstract: The fundamental phenomenon of Bose-Einstein Condensation (BEC) has been observed in different systems of real and quasi-particles. The condensation of real particles is achieved through a major reduction in temperature while for quasi-particles a mechanism of external injection of bosons by irradiation is required. Here, we present a novel and universal approach to enable BEC of quasi-particles an… ▽ More The fundamental phenomenon of Bose-Einstein Condensation (BEC) has been observed in different systems of real and quasi-particles. The condensation of real particles is achieved through a major reduction in temperature while for quasi-particles a mechanism of external injection of bosons by irradiation is required. Here, we present a novel and universal approach to enable BEC of quasi-particles and to corroborate it experimentally by using magnons as the Bose-particle model system. The critical point to this approach is the introduction of a disequilibrium of magnons with the phonon bath. After heating to an elevated temperature, a sudden decrease in the temperature of the phonons, which is approximately instant on the time scales of the magnon system, results in a large excess of incoherent magnons. The consequent spectral redistribution of these magnons triggers the Bose-Einstein condensation. △ Less

Submitted 8 February, 2020; v1 submitted 21 December, 2016; originally announced December 2016.

Comments: In contrast to the previous version additional information has been added. The chemical potential was derived from BLS measurements, the influence of the spin Seebeck effect is discussed more extensively in the Supplement with respect to the theoretical model and the rapid cooling has been realized in Au/Al/YIG structures where no substantial contribution of the spin Seebeck effect is expected

Gilbert damping of magnetostatic modes in a yttrium iron garnet sphere

Authors: Stefan Klingler, Hannes Maier-Flaig, Carsten Dubs, Oleskii Surzhenko, Rudolf Gross, Hans Huebl, Sebastian T. B. Goennenwein, Mathias Weiler

Abstract: The magnetostatic mode (MSM) spectrum of a 300$μ$m diameter single crystalline sphere of yttrium iron garnet is investigated using broadband ferromagnetic resonance (FMR). The individual MSMs are identified via their characteristic dispersion relations and the corresponding mode number tuples $(nmr)$ are assigned. Taking FMR data over a broad frequency and magnetic field range allows to analyze bo… ▽ More The magnetostatic mode (MSM) spectrum of a 300$μ$m diameter single crystalline sphere of yttrium iron garnet is investigated using broadband ferromagnetic resonance (FMR). The individual MSMs are identified via their characteristic dispersion relations and the corresponding mode number tuples $(nmr)$ are assigned. Taking FMR data over a broad frequency and magnetic field range allows to analyze both the Gilbert damping parameter~$α$ and the inhomogeneous line broadening contribution to the total linewidth of the MSMs separately. The linewidth analysis shows that all MSMs share the same Gilbert damping parameter $α=2.7(5) \times 10^{-5}$ irrespective of their mode index. In contrast, the inhomogeneous line broadening shows a pronounced mode dependence. This observation is modeled in terms of two-magnon scattering processes of the MSMs into the spin-wave manifold, mediated by surface and volume defects. △ Less

Submitted 7 December, 2016; originally announced December 2016.

Comments: 5 pages, 3 figures

Journal ref: Appl. Phys. Lett. 110, 092409 (2017

Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses

Authors: Carsten Dubs, Oleksii Surzhenko, Ralf Linke, Andreas Danilewsky, Uwe Brückner, Jan Dellith

Abstract: Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG) films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have been grown as a basic material for spin-wave propagation experiments in microstructured waveguides. The continuously strained films exhibit nearly perfect crystallinity without significant mosaicity and with effective lattice misfits of delta a(… ▽ More Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG) films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have been grown as a basic material for spin-wave propagation experiments in microstructured waveguides. The continuously strained films exhibit nearly perfect crystallinity without significant mosaicity and with effective lattice misfits of delta a(perpendicular)/a(substrate) ~10-4 and below. The film/substrate interface is extremely sharp without broad interdiffusion layer formation. All LPE films exhibit a nearly bulk-like saturation magnetization of (1800+-20) Gs and an `easy cone' anisotropy type with extremely small in-plane coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No significant out-of-plane anisotropy is observed, but a weak dependence of the effective magnetization on the lattice misfit is detected. The narrowest ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is the lowest value reported so far for YIG films of 100 nm thicknesses and below. The Gilbert damping coefficient for investigated LPE films is estimated to be close to 1 x 10-4. △ Less

Submitted 29 August, 2016; originally announced August 2016.

Comments: 8 pages, 10 figures

Journal ref: J. Phys. D: Appl. Phys. 50 (2017) 204005

Spatially resolved detection of complex ferromagnetic dynamics using optically detected NV spins

Authors: Chris. S. Wolfe, Sergei. A. Manuilov, Carola. M. Purser, Richelle Teeling-Smith, Carsten. Dubs, P. Chris Hammel, Vidya Praveen Bhallamudi

Abstract: We demonstrate optical detection of a broad spectrum of ferromagnetic excitations using nitrogen-vacancy (NV) centers in an ensemble of nanodiamonds. Our recently developed approach exploits a straightforward CW detection scheme using readily available diamond detectors, making it easily implementable. The NV center is a local detector, giving the technique spatial resolution, which here is define… ▽ More We demonstrate optical detection of a broad spectrum of ferromagnetic excitations using nitrogen-vacancy (NV) centers in an ensemble of nanodiamonds. Our recently developed approach exploits a straightforward CW detection scheme using readily available diamond detectors, making it easily implementable. The NV center is a local detector, giving the technique spatial resolution, which here is defined by our laser spot, but in principle can be extended far into the nanoscale. Among the excitations we observe are propagating dipolar and dipolar-exchange spinwaves, as well as dynamics associated with the multi-domain state of the ferromagnet at low fields. These results offer an approach, distinct from commonly used ODMR techniques, for spatially resolved spectroscopic study of magnetization dynamics at the nanoscale. △ Less

Submitted 23 February, 2016; v1 submitted 16 December, 2015; originally announced December 2015.

Comments: 6 pages and 1 page supplmentary information

Journal ref: Applied Physics Letters 108, 232409 (2016

Spin-transfer torque based damping control of parametrically excited spin waves in a magnetic insulator

Authors: V. Lauer, D. A. Bozhko, T. Brächer, P. Pirro, V. I. Vasyuchka, A. A. Serga, M. B. Jungfleisch, M. Agrawal, Yu. V. Kobljanskyj, G. A. Melkov, C. Dubs, B. Hillebrands, A. V. Chumak

Abstract: The damping of spin waves parametrically excited in the magnetic insulator Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an adjacent normal-metal film. The experiment is performed on a macroscopically sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave relaxation frequency is determined via the threshold of the parametric instability measured by… ▽ More The damping of spin waves parametrically excited in the magnetic insulator Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an adjacent normal-metal film. The experiment is performed on a macroscopically sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave relaxation frequency is determined via the threshold of the parametric instability measured by Brillouin light scattering (BLS) spectroscopy. The application of a dc current to the Pt film leads to the formation of a spin-polarized electron current normal to the film plane due to the spin Hall effect (SHE). This spin current exerts a spin transfer torque (STT) in the YIG film and, thus, changes the spin-wave damping. Depending on the polarity of the applied dc current with respect to the magnetization direction, the damping can be increased or decreased. The magnitude of its variation is proportional to the applied current. A variation in the relaxation frequency of +/-7.5% is achieved for an applied dc current density of 5*10^10 A/m^2. △ Less

Submitted 29 August, 2015; originally announced August 2015.

Journal ref: Appl. Phys. Lett. 108, 012402 (2016)

Measurements of the exchange stiffness of YIG films by microwave resonance techniques

Authors: Stefan Klingler, Andrii V. Chumak, Tim Mewes, Behrouz Khodadadi, Claudia Mewes, Carsten Dubs, Oleksii Surzhenko, Burkard Hillebrands, Andrés Conca

Abstract: Measurements of the exchange stiffness $D$ and the exchange constant $A$ of Yttrium Iron Garnet (YIG) films are presented. The YIG films with thicknesses from 0.9 $μ$m to 2.6 $μ$m were investigated with a microwave setup in a wide frequency range from 5 to 40 GHz. The measurements were performed when the external static magnetic field was applied in-plane and out-of-plane. The method of Schreiber… ▽ More Measurements of the exchange stiffness $D$ and the exchange constant $A$ of Yttrium Iron Garnet (YIG) films are presented. The YIG films with thicknesses from 0.9 $μ$m to 2.6 $μ$m were investigated with a microwave setup in a wide frequency range from 5 to 40 GHz. The measurements were performed when the external static magnetic field was applied in-plane and out-of-plane. The method of Schreiber and Frait, based on the analysis of the perpendicular standing spin wave (PSSW) mode frequency dependence on the applied out-of-plane magnetic field, was used to obtain the exchange stiffness $D$. This method was modified to avoid the influence of internal magnetic fields during the determination of the exchange stiffness. Furthermore, the method was adapted for in-plane measurements as well. The results obtained using all methods are compared and values of $D$ between $(5.18\pm0.01) \cdot 10^{-17}$T$\cdot$m$^2$ and $(5.34\pm0.02) \cdot 10^{-17}$ T$\cdot$m$^2$ were obtained for different thicknesses. From this the exchange constant was calculated to be $A=(3.65 \pm 0.38)~$pJ/m. △ Less

Submitted 25 August, 2014; originally announced August 2014.

Comments: 10 pages, 3 figures, 3 tables

Journal ref: J. Phys. D: Appl. Phys. 48 (2015) 015001 (5pp)

Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet (YIG)/Pt bilayers

Authors: P. Pirro, T. Brächer, A. Chumak, B. Lägel, C. Dubs, O. Surzhenko, P. Görnet, B. Leven, B. Hillebrands

Abstract: We present an experimental study of spin-wave excitation and propagation in microstructured waveguides patterned from a 100 nm thick yttrium iron garnet (YIG)/platinum (Pt) bilayer. The life time of the spin waves is found to be more than an order of magnitude higher than in comparably sized metallic structures despite the fact that the Pt capping enhances the Gilbert damping. Utilizing microfocus… ▽ More We present an experimental study of spin-wave excitation and propagation in microstructured waveguides patterned from a 100 nm thick yttrium iron garnet (YIG)/platinum (Pt) bilayer. The life time of the spin waves is found to be more than an order of magnitude higher than in comparably sized metallic structures despite the fact that the Pt capping enhances the Gilbert damping. Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the spin-wave mode structure for different excitation frequencies. An exponential spin-wave amplitude decay length of 31 μm is observed which is a significant step towards low damping, insulator based micro-magnonics. △ Less

Submitted 25 November, 2013; originally announced November 2013.

Journal ref: Appl Phys Lett 104, 2402 (2014)