First-principles theory of magnetocrystalline anisotropy of disordered alloys: Application to cobalt platinum

We present a first-principles theory of magnetocrystalline anisotropy of disordered alloys within the framework of the spin-polarized fully relativistic Korringa-Kohn-Rostoker coherent-potential approximation in which relativistic effects such as spin-orbit coupling and magnetization are treated on an equal footing. Unlike in some other methods, we calculate the magnetocrystalline anisotropy energy (MAE) of a material directly rather than subtracting the total energies of the material for two magnetization directions calculated separately. Since the total energy of a system is several orders of magnitude larger than its MAE (similar to mu eV), this approach provides a robust method. Our predictions of the MAE and magnetic easy axis of elemental bcc-Fe, fee-Co, and fcc-Ni are in reasonable accord with previous calculations as well as with the experimental results. We calculate the MAE of disordered fcc-CoxPt1-x alloys for x = 0.25, 0.5, and 0.75 and find that the magnetic easy axis for these alloys is along the [111] direction of the crystal, and that the magnitude of MAE is largest for the equiatomic composition. We also find that the magnitude of MAE decreases with temperature in these alloys, but the magnetic easy axis remains unchanged.