Finite-temperature anisotropy of magnetic alloys

The temperature dependence of the magnetic anisotropy of ferromagnetic materials is analyzed. Simple ferromagnets, such as Fe and Co, obey the m = n ( n + 1 ) ∕ 2 power laws predicted by the Callen and Callen [ Phys. Rev. 129 , 578 ( 1963 ) ] theory, but in alloys, the applicability of the theory is an exception rather than the rule. Many alloys, such as the rare-earth transition-metal intermetallics and L 1 0 magnets, violate a basic assumption of the theory, namely, that the single-ion anisotropy and the spontaneous magnetization have the same origin. This is the reason for significant deviations from the Callen and Callen behavior, such as the m = 2 law we obtained for L 1 0 alloys.