Finite-temperature anisotropy of PtCo magnets

The temperature dependence of the magnetocrystalline anisotropy of PtCo and its atomic origin are investigated by first-principle and model calculations. The Pt spin moment necessary to realize the leading 5d anisotropy contribution is due to neighboring Co atoms. At finite temperatures, Co spin disorder strongly reduces the Pt moment and the anisotropy. This is in contrast to the situation encountered in 3d and 3d-4f magnets, where the atomic magnetic moments remain largely conserved, even above the Curie temperature. A consequence of the L1₀ mechanism is that the K₁(T) curve of exhibits a negative curvature, in contrast to the unfavorable positive curvature for rare-earth transition-metal magnets.