Relation between Ga ordering and magnetostriction of Fe-Ga alloys studied by x-ray diffuse scattering

Abstract

Transmission synchrotron diffraction was employed to characterize the Ga ordering in magnetostrictive ${\text{Fe}}_{100\ensuremath{-}x}{\text{Ga}}_{x}$ alloys with Ga concentrations from 0 to $20.3\text{ }\text{at}\text{.}\text{ }\mathrm{%}$. The experiments focused on the development of atomic short-range ordering (SRO) by analysis of the diffuse scattering appearing at superlattice positions of the $\text{D}{0}_{3}$ ordered alloy structure. No SRO was found for Ga concentrations less than $4\text{ }\text{at}\text{.}\text{ }\mathrm{%}$. Between 13 and $20.3\text{ }\text{at}\text{.}\text{ }\mathrm{%}$, $\text{D}{0}_{3}$-type SRO clusters are observed whose size increases with Ga concentration for both slow-cooled and quenched samples. Thermal quenching of the samples suppresses the cluster sizes when compared to slow-cooled samples of the same concentration. For quenched samples with large Ga concentration, Ga pairing is evidenced by growing B2-type correlations. At low concentrations, the presence of SRO appears to have little (if any) effect on the enhanced magnetostriction. However, the dramatic suppression of magnetostriction near $\ensuremath{\sim}20\text{ }\text{at}\text{.}\text{ }\mathrm{%}$ Ga can be linked rapid growth of SRO just before the onset of long-range chemical order.