Tetragonal phases in Fe-Ga alloys: A quantitative study

Currently, the dominant model for the formation of enhanced magnetostriction of Fe-Ga alloys is based on the assumption of the presence of microscopic inclusions with a tetragonal $L{6}_0$ structure in the cubic matrix of the alloy. However, no evidence for the presence of this phase in the bulk of the alloys in amounts sufficient to have a noticeable effect on the magnitude of magnetostriction has been obtained so far. To test this hypothesis, a detailed scanning of the reciprocal space of $\mathrm{F}{\mathrm{e}}_{81}\mathrm{G}{\mathrm{a}}_{19}\mathrm{T}{\mathrm{b}}_{0.1}$ and ${\mathrm{Fe}}_{73}{\mathrm{Ga}}_{27}$ single crystals was carried out at ESRF at high photon flux stations. In particular, it was possible to reliably record superstructure diffraction peaks, the intensity of which was at a level of $2\times {10}^{-6}$ from the intensity of the fundamental peaks. Nevertheless, neither the presence of superstructure diffraction peaks obviously belonging to the $L{6}_0$ phase nor the tetragonal splitting of the fundamental diffraction peaks into components, which could indicate the presence of this phase in the samples, was detected. Similar results were obtained using complementary methods (electron and neutron diffraction). Based on the performed analysis of the background level in the places of the expected positions of superstructure peaks of the $L{6}_0$ phase, it was found that the volume fraction of this phase in the $\mathrm{F}{\mathrm{e}}_{81}\mathrm{G}{\mathrm{a}}_{19}\mathrm{T}{\mathrm{b}}_{0.1}$ alloy cannot exceed 0.2 %. The presence of a previously discovered $X$ phase with hexagonal or orthorhombic symmetry in a crystal with 27 at. % Ga was confirmed.