Ab initio calculations of temperature-dependent magnetostriction of Fe and A2Fe1−xGax within the disordered local moment picture

Abstract

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) Fe 1−x Ga x (0 x 0.2) alloys to describe the temperature dependence of their magnetoelasticity. The finite-temperature magnetoelasticity, in particular the magnetoelastic constant B 1 , 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 B 1 have been performed on bcc Fe across its ferromagnetic temperature range. Our results show good qualitative agreement with experiment, in particular reproducing the anomalous, nonmonotonic 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 Fe 1−x Ga x 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 nonmonotonic temperature dependence and significant volume dependence are suppressed by increasing Ga content.

Ab initiotheory of the Gibbs free energy and a hierarchy of local moment correlation functions in itinerant electron systems: The magnetism of theMn3Amaterials class

“…However, as magnetic order increases, by reducing the temperature or applying an external magnetic field for example, {m n } increase in size and so higher order terms become important and must be considered in Eqs. (31) and (34). In other words, the presence of beyond pairwise Heisenberglike interactions among the local moments, {ê n }, has the effect of changing the magnetic behavior as the ordering develops at each site, which is reflected from a nonlinear nature of h int n in Eq.…”

“…In other words, the presence of beyond pairwise Heisenberglike interactions among the local moments, {ê n }, has the effect of changing the magnetic behavior as the ordering develops at each site, which is reflected from a nonlinear nature of h int n in Eq. (34). The meaning of this is that thermal fluctuations of {ê n } at different states of magnetic order can induce alterations on the electronic structure.…”

Spin Orientation and Magnetostriction of Tb1−xDyxFe2 from First Principles

“…Due to their itinerant electron origin, the constants B γ ,2 itin and B ,2 itin cannot be obtained from CF theory. They are, however, amenable to treatment in the DFT-based disorderedlocal-moment picture [27,33]. We describe these calculations in Sec.…”

“…We calculate E itin (ê, ε) for GdFe 2 using the same method demonstrated recently for bcc Fe and Fe-Ga alloys [33]. This approach is a Green's function multiplescattering theory-based formulation of the disorderedlocal-moment picture within DFT (DFT-DLM [27]), which-as discussed in Sec.…”

“…As described in Ref. [33], calculation of the derivative of the total energy with respect to the magnetization angle for different strain states allows the anisotropy and magnetoelastic constants to be obtained.…”