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An ab-initio theory for the temperature dependence of magnetic anisotropy

J. B. Staunton·L. Szunyogh·A. Buruzs·B. L. Gyorffy·S. Ostanin·L. Udvardi
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Abstract

We present a first-principles theory of the variation of magnetic anisotropy, K, with temperature, T, in metallic ferromagnets. It is based on relativistic electronic structure theory and calculation of magnetic torque. Thermally induced `local moment' magnetic fluctuations are described within the relativistic generalisation of the `disordered local moment' (R-DLM) theory from which the T dependence of the magnetisation, m, is found. We apply the theory to a uniaxial magnetic material with tetragonal crystal symmetry, L1_0-ordered FePd, and find its uniaxial K consistent with a magnetic easy axis perpendicular to the Fe/Pd layers for all m and proportional to m squared for a broad range of values of m. This is the same trend that we have previously found in L1_0-ordered FePt and which agrees with experiment. This account, however, differs qualitatively from that extracted from a single ion anisotropy model. We also study the magnetically soft cubic magnet, the Fe(50)Pt(50) solid solution, and find that its small magnetic anisotropy constant K_1 rapidly diminishes from 8 micro-eV to zero. K evolves from being proportional to the seventh power of m at low T to the fourth power near the Curie temperature.

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J. B. Staunton, L. Szunyogh, A. Buruzs, B. L. Gyorffy, S. Ostanin, L. Udvardi. 2006-06-08. An ab-initio theory for the temperature dependence of magnetic anisotropy. https://arxiv.org/abs/cond-mat/0606219

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