Ab initio calculations of temperature-dependent magnetostriction of Fe and A2 Fe1−xGax within the disordered local moment picture

The fully relativistic disordered local moment (DLM) theory is used to perform calculations of the magnetic torque of tetragonally distorted Fe and fully disordered (A2) Fe1−xGax (0≤x≤0.2) alloys to describe the temperature-dependence of their magnetoelasticity. The finite temperature magnetoelasticity, in particular the magnetoelastic constant B1, is obtained within DLM theory by studying the response of the magnetic torque generated by the magnetocrystalline anisotropy to the application of a tetragonal strain. Calculations of B1 have been performed on bcc Fe across its ferromagnetic temperature range. Our results show good qualitative agreement with experiment, in particular reproducing the anomalous, non-monotonic thermal behavior of bcc Fe’s magnetostriction, which has been largely unexplained for more than 50 years. The method has also been used to calculate the finite temperature magnetoelasticity of the A2 phase of Fe1−xGax alloys as a starting point for further investigations into the giant magnetostriction of Galfenol alloys. Our calculations show that homogeneously doping bcc Fe with Ga does not produce an enhancement in magnetostriction and that the non-monotonic temperature dependence and significant volume dependence are suppressed by increasing Ga content