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

Transmission synchrotron diffraction was employed to characterize the Ga ordering in magnetostrictive Fe100-xGax alloys with Ga concentrations from 0 to 20.3 at.%. The experiments focused on the development of atomic short-range ordering (SRO) by analysis of the diffuse scattering appearing at superlattice positions of the D03 ordered alloy structure. No SRO was found for Ga concentrations less than 4 at. %. Between 13 and 20.3 at. %, D03-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 ∼ 20 at. % Ga can be linked rapid growth of SRO just before the onset of long-range chemical order.