Phase analysis of near equiatomic bulk FeRh alloys: X-ray versus neutron diffraction and magnetization measurements

Abstract

The information obtained by X-ray diffraction (XRD) by impinging the X-ray beam onto the flat surface of bulk Fe–Rh alloys is contrasted with that provided by the thermomagnetic analysis curves measured under a magnetic field of 5 mT and 2 T, and the neutron diffraction (ND) patterns. The experiments were performed on slices cut from bulk Fe50Rh50 and Fe49Rh51 alloys prepared by induction melting followed by 48 h of thermal annealing at 1273 K. Whereas ND patterns and magnetization curves, directly and indirectly point out that the samples are single-phase with a CsCl-type crystal structure undergoing a magnetoelastic transition that changes the magnetic structure from antiferromagnetic to ferromagnetic on heating, multiple phases are identified in the XRD patterns, which modify upon polishing or etching the surface with a mixture of hydrochloric (HCl) and nitric acid (HNO3) at a volume ratio of 90:10 from 30 to 210 min. The limitation of XRD for accurately characterizing the phase constitution within the bulk of Fe–Rh alloys is underlined.