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 generalization of the disordered local moment theory from which the T dependence of the magnetization, m, is found. We apply the theory to a uniaxial magnetic material with tetragonal crystal symmetry, L 10 -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 m2 for a broad range of values of m. This is the same trend that we have previously found in L 10 -ordered FePt and which agrees with experiment. We also study a magnetically soft cubic magnet, the Fe50 Pt50 solid solution, and find that its small magnetic anisotropy constant K1 rapidly diminishes from 8 μeV to zero. K1 evolves from being proportional to m7 at low T to m4 near the Curie temperature. The accounts of both the tetragonal and cubic itinerant electron magnets differ from those extracted from single ion anisotropy models and instead receive clear interpretations in terms of two ion anisotropic exchange.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Oct 23 2006|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics