Magnetism and structural ordering on a bcc lattice for highly magnetostrictive Fe-Ga alloys: A coherent potential approximation study

We calculate the electronic structure, magnetic moments, and ordering energies of highly magnetostrictive Fe1-xGax alloys from first-principles in the composition range up to x=0.25. The coherent potential approximation was used to treat effects of chemical disorder. Given an underlying bcc lattice in whole range compositions investigated, the DO3 type of ordering is found to have a lower energy than A2- and B2-type structures. We find that ordering energies strongly depend on the state of magnetic order such that thermal magnetic disorder strongly favors chemical ordering (DO3 and B2). The values of the magnetic moments of Fe on different sublattices of ordered structures are found to have a distinctive dependency on the Ga concentration. By taking into account the results of earlier fully relativistic and full potential calculations of magnetostriction for ordered stoichiometric Fe3Ga compounds and available experimental phenomenology, our results for disordered alloys suggest an eventually more complex origin of the giant magnetostriction in Fe-Ga alloys than it would appear from a simple electronic structure analysis of ordered stoichiometric compounds. (C) 2008 American Institute of Physics.