Effects of spin fluctuation on the magnetic anisotropy constant of itinerant electron magnets

In the disordered local moment picture, we calculated the magnetization (M) and magnetic anisotropy energy (MAE) of FePt, CoPt, and MnAl ordered alloys and a body-centered tetragonal FeCo (bct-FeCo) disordered alloy, assuming spatially fluctuated spin configurations at finite temperatures. All alloys exhibit the relation K1(T)/K1(0) = (M(T)/M(0))n with the exponent n 2. This is consistent with the two-ion anisotropy model, in contrast to the usual single-ion anisotropy model exhibiting n = 3. Because these systems have different mechanisms of MAE, we suggest that this relation is a general rule for itinerant electron systems.