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LDA+DMFT Approach to Magnetocrystalline Anisotropy of Strong Magnets

Jian-Xin Zhu1,*, Marc Janoschek1, Richard Rosenberg2, Filip Ronning1, J. D. Thompson1, Michael A. Torrez1, Eric D. Bauer1, and Cristian D. Batista1,†

  • 1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  • 2Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
  • *jxzhu@lanl.gov
  • †cdb@lanl.gov
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Phys. Rev. X 4, 021027 – Published 15 May, 2014

DOI: https://doi.org/10.1103/PhysRevX.4.021027

Abstract

The new challenges posed by the need of finding strong rare-earth-free magnets demand methods that can predict magnetization and magnetocrystalline anisotropy energy (MAE). We argue that correlated electron effects, which are normally underestimated in band-structure calculations, play a crucial role in the development of the orbital component of the magnetic moments. Because magnetic anisotropy arises from this orbital component, the ability to include correlation effects has profound consequences on our predictive power of the MAE of strong magnets. Here, we show that incorporating the local effects of electronic correlations with dynamical mean-field theory provides reliable estimates of the orbital moment, the mass enhancement, and the MAE of YCo5.

Popular Summary

Magnetic materials are widely used in technologies ranging from wind turbines to “green” automobiles. Compounds with large magnetocrystalline anisotropies are typically difficult to demagnetize, which is technologically advantageous. Magnetocrystalline anisotropy is inherently strong in heavy, rare-earth elements, but the scarcity of these elements has led scientists to investigate using transition-metal-based compounds as replacements. We demonstrate for the first time how electronic correlations determine the magnetocrystalline anisotropy of transition metals, using the yttrium-cobalt compound YCo5 as a prototypical substance.

We find that the orbital magnetic moment of YCo5 differs from estimates based on covalent-band theory—we propose that this discrepancy is due to dynamical electron correlations. Spin-orbit interactions are weak in transition-metal compounds, and in general, their magnetocrystalline anisotropy depends on a delicate balance of competing interactions: Coulomb repulsion, ligand fields, spin-orbit coupling, and material-dependent hybridization. We apply a dynamical mean-field theoretical approach in combination with density-functional theory—which takes into account the competing interactions—to the representative rare-earth-free magnet YCo5. We demonstrate for the first time the important role of electronic correlations in determining the magnetocrystalline anisotropy.

Our reliable estimates of the orbital moment, mass enhancement, and the magnetocrystalline anisotropy of YCo5 provide critical knowledge and new insight into the design of rare-earth-free magnets and complex magnetic functionality in general.

Article Text

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Outline

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Phys. Rev. X 4, 021027– Published 15 May, 2014
  • Received 22 February 2014
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