Structurally heterogeneous model of extrinsic magnetostriction for Fe-Ga and similar magnetic alloys: Part I. Decomposition and confined displacive transformation

A compositionally and Structurally heterogeneous model for ferromagnetic alloys has been developed and applied to Fe-Ga alloys that exhibit giant magnetostriction. Our model assumes that the Fe-Ga bcc solid solution near its solubility limit is a coarsening-resistant nanodispersion of a DO3 phase that is formed due to coherency lifting by excess vacancies, as is known to be the case for chemically similar Fe-Al alloys. This compositionally heterogeneous state undergoes a cubic -> tetragonal displacive transformation that brings the structure closer to an equilibrium fcc-based L1(2) ordered phase. The predictions of our theory are in agreement with existing electron microscopy and X-ray diffraction observations.