Magnetic anisotropies of Ni–Pt and Co–Pt alloys

We present the magnetocrystalline anisotropy of disordered Ni1−xPtx and disordered fcc Co1−xPtx alloys using the spin-polarized relativistic Korringa–Kohn–Rostoker coherent-potential approximation in which the spin-orbit coupling and magnetism are treated on an equal footing. In both the pure fcc ferromagnetic elements (Ni as well as Co), the magnetic easy axis is along the [111] direction of the crystal. Addition of Pt to Ni changes the magnetic easy axis to the [001] direction, in agreement with the experimental observations, although the magnitudes of the calculated magnetocrystalline anisotropy energies for different compositions are somewhat different from the corresponding experimental values. In contrast, addition of Pt to Co does not alter the magnetic easy axis, only the magnitude of the magnetocrystalline anisotropy energy is affected. The origin of this contrasting behavior may lie in the larger size of the magnetic moment of Co (as compared to Ni).