Ab initio theoretical description of the dependence of magnetocrystalline anisotropy on both compositional order and lattice distortion in transitionmetal alloys - art. no. 014411

Recently, we outlined a scheme to investigate the effects of both short-ran ged and long-ranged compositional order on the magnetocrystalline anisotrop y of alloys from a first-principles electronic structure point of view [Phy s. Rev. Lett. 82, 5369 (1999)] and showed that in the Co0.5Pt0.5 alloy comp ositional order enhances the magnitude of magnetocrystalline anisotropy ene rgy (MAE) by some two orders of magnitude. Here we describe our scheme in d erail and study some more transition metal alloys. In the Co0.25Pt0.75 allo y we find the perfect L1(2) structure to be magnetically soft whereas impos ition of directional order greatly enhances its MAE. We also present the ef fect of lattice distortion (tetragonalization) on MAE on the same footing a cid find that in the Co0.5Pt0.5 alloy it accounts for only about 20% of the observed enhancement, thus confirming that compositional order is the majo r player in this effect. Tetragonalization of the lattice has also a modest effect on the MAE of the Fe0.5Co0.5 alloy. We also examine the electronic effects which underpin the directional chemical order that is produced by m agnetic annealing of permalloy which we study within the same framework.