Ab Initio Theoretical Description of the Interrelation between Magnetocrystalline Anisotropy and Atomic Short - Range Order

The cubic lattice symmetry of ferromagnetic homogeneously disordered alloys is broken when a compositional modulation is imposed. This can have a profound influence on the magnetocrystalline anisotropy energy (MAE). We describe our ab initio theory of this effect and use the framework of concentration waves with the electronic structure described within the spin-polarised relativistic Korringa-Kohn-Rostoker coherent-potential approximation. We find that ordering produces a 2 order of magnitude increase in the MAE as well as altering the equilibrium direction of magnetisation. Using the same theoretical framework we also examine directional compositional order produced by magnetic annealing with an explicit study of permalloy.