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Tunable laser-generated GHz surface acoustic waves during magnetostructural phase transition in FeRh thin films
Authors:
Ia. A. Mogunov,
A. Yu. Klokov,
N. Yu. Frolov,
A. V. Protasov,
G. E. Zhezlyaev,
D. I. Devyaterikov,
R. R. Gimaev,
V. I. Zverev,
A. M. Kalashnikova
Abstract:
Laser-generated surface acoustic waves (SAW) facilitate an efficient information processing in modern spintronics and magnonics. The ability to tune SAW parameters is crucial to achieve an acoustic control over magnonic properties. Such tunability can be achieved in phase-changing magnetic materials accommodating both spin waves and SAWs. A promising material is FeRh alloy, a metallic antiferromag…
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Laser-generated surface acoustic waves (SAW) facilitate an efficient information processing in modern spintronics and magnonics. The ability to tune SAW parameters is crucial to achieve an acoustic control over magnonic properties. Such tunability can be achieved in phase-changing magnetic materials accommodating both spin waves and SAWs. A promising material is FeRh alloy, a metallic antiferromagnet at room temperature undergoing a phase transition into ferromagnetic state accompanied by a crystal lattice expansion at 370 K. This transition can also be induced by femtosecond laser pulses. In this paper we use the phase transition in 60 nm Fe49Rh51 film to optically generate pulses of Gigahertz quasi-Rayleigh SAWs. We detect them via photoelastic effect and show that the lattice transformation during phase transition is a dominant strain-generation mechanism for above-threshold excitation. The weight of this contribution rises as the sample is heated closer to AFM-FM transition temperature and 'switches off' when heated above it allowing to control the SAW amplitude. A model based on thermodynamical parameters of Fe49Rh51 shows that the lattice transformation occurring within 95 ps effectively contributes to SAW generation happening at a comparable timescale, while non-equilibrium fast kinetics of the phase transition does not.
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Submitted 12 November, 2025;
originally announced November 2025.
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Surface acoustic wave enabled all-optical determination of the interlayer elastic constants of van der Waals interface
Authors:
N. Yu. Frolov,
A. Yu. Klokov,
A. I. Sharkov,
M. V. Pugachev,
A. Yu. Kuntsevich
Abstract:
Understanding the properties of two-dimensional materials interfaces with the substrate is necessary for device applications. Surface acoustic wave propagation through the layered material flake on a substrate could provide unique information on the transverse rigidity of the flake-to-substrate interaction. We generate ultrasonic waves by a focused femtosecond laser pulse at the surface of the mod…
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Understanding the properties of two-dimensional materials interfaces with the substrate is necessary for device applications. Surface acoustic wave propagation through the layered material flake on a substrate could provide unique information on the transverse rigidity of the flake-to-substrate interaction. We generate ultrasonic waves by a focused femtosecond laser pulse at the surface of the model system -- fused silica with h-BN flake transferred above. Using an all-optical spatially resolved pump-probe interferometric technique, we measure the spatial dependencies of the surface vertical velocity profiles. Our measurements reveal the appearance of the surface acoustic wave dispersion in the hBN flake region compared to fused silica surface. Multilayer modeling allows us to gain access to longitudinal and shear elastic coupling constants $c^*_{33}$ and $c^*_{44}$ between hexagonal BN and substrate.
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Submitted 7 November, 2025;
originally announced November 2025.
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3D Hypersound Microscopy of Van der Waals Heterostructures
Authors:
A. Yu. Klokov,
N. Yu. Frolov,
A. I. Sharkov,
S. N. Nikolaev,
S. I. Chentsov,
M. A. Chernopitssky,
M. V. Pugachev,
A. I. Duleba,
A. V. Shupletsov,
V. S. Krivobok,
A. Yu. Kuntsevich
Abstract:
We employ here a picosecond ultrasonic technique to study Van der Waals heterostructures. Temporal variation of the reflection coefficient of the Al film that covers Van der Waals hBN/WSe$_2$/hBN heterostructures on a sapphire substrate after the femtosecond laser pulse excitation is carefully measured using an interferometric technique with spatial resolution. The laser pulse generates a broadban…
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We employ here a picosecond ultrasonic technique to study Van der Waals heterostructures. Temporal variation of the reflection coefficient of the Al film that covers Van der Waals hBN/WSe$_2$/hBN heterostructures on a sapphire substrate after the femtosecond laser pulse excitation is carefully measured using an interferometric technique with spatial resolution. The laser pulse generates a broadband sound wave packet in aluminum film propagating perpendicular to the plane direction and partially reflecting from the heterostructural interfaces. The demonstrated technique has enough sensitivity to resolve a WSe$_2$ monolayer embedded in hBN. We apply a multilayered model of the optical and acoustical response that allows to evaluate the mechanical parameters, in particular, rigidity of interfaces, inaccessible from the other measurements. Mapping of the Fourier spectra of the response clearly visualizes different composition regions and can therefore serve as an acoustic tomography tool. Our findings demonstrate almost zero acoustic phonon dissipation below 150 GHz at the interfaces and in the layers that makes Van der Waals heterostructures perspective for nano-acoustical applications.
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Submitted 8 November, 2021;
originally announced November 2021.