Bulk vs. surface structural phases in Fe-27Ga alloy

Abstract

The crystal structure of the bulk quenched Fe-27Ga alloy has been studied using high-resolution neutron and X-ray diffraction to determine the phase distribution over the volume of the material. Neutron diffraction results have shown that the bulk sample consists of completely ordered D03 phase. X-ray diffraction (XRD) with a long acquisition time has allowed investigating precisely the surface layer with a thickness of ∼ 4–16 µm after surface preparation by different methods. The obtained results have confirmed the presence of the ordered D03 phase. Additionally, the required mechanical and/or chemical treatments of the sample for the XRD experiments led to the formation of extra phases with less ordered structures, B2 and A2, in the surface layer. It has been found that the ratio and volume fraction of the additional phases depend on contact duration of the alloy with the air atmosphere. Existence of significant amounts of m-D03 phase, which is considered by several authors to be responsible for the giant magnetostriction of Fe-Ga alloy, is excluded by both neutron and XRD data.