ON THE QUESTION OF THE MECHANISM OF FORMATION AND STABILITY OF THE INDUCED MAGNETIC ANISOTROPY AND DOMAIN STRUCTURE IN SOFT MAGNETIC Fe–18 at%Ga ALLOY SINGLE CRYSTALS

The influence of thermomagnetic treatment (TMT) including annealing and cooling of the alloy in a constant magnetic field of 10 kOe applied both along the <100> direction and across one on the magnetostriction of single-crystal samples of the Fe–18 at % Ga alloy has been studied. The samples in the form of thin disks had the “Goss” orientation of the crystallographic axes – {011}<100>. The field dependences of the longitudinal – λ100 and transverse – λ100 ⊥ magnetostriction coefficients were measured before and after TMT. By comparison with literature sources dealing with domain structure, it is shown that magnetoelastic properties correspond to the type of domain structure in alloy samples after slow cooling without external influences (before TMT) and after TMT in a magnetic field parallel or perpendicular to the easy magnetization axis [001] lying in the plane of the sample. Before and after TMT, in a field parallel to the [001] axis, there is a small longitudinal magnetostriction λ100 within a few tens of ppm, while its transverse component λ100 ⊥ is negative and reaches an absolute value of 160–190 ppm. This corresponds to a stripe domain structure, when the magnetization is predominantly oriented parallel to the [001] axis. If during TMT the magnetic field was applied perpendicular to the [001] axis and parallel to the [110] axis, then after TMT a twofold increase in the coefficient λ100 and a 40 percent decrease in λ100 ⊥ are observed. Such changes in magnetoelastic deformation indicate the formation of a transverse domain structure, the domains in which are predominantly magnetized parallel to the [100] and [010] axes. The observed TMT effects and their stability under normal conditions are explained by the directional ordering of Ga–Ga pairs in the bcc lattice of the Fe–Ga alloy.