Mössbauer Study of Hyperfine Fields and Isomer Shifts in the Fe-Rh Alloys

Hyperfine fields and isomer shifts of Fe⁵⁷ in the Fe-Rh system have been investigated by the M\"ossbauer technique in the composition range between 0 and 52 at.% Rh. When the Rh concentration exceeds 20%, chemical ordering of CsCl type develops and two distinct hyperfine fields are observed, corresponding to Fe on Fe sites (FeI) and Fe on Rh sites (FeII). For example, Hᵢ(I)=277 kOe and Hᵢ(II)=384 kOe in an alloy containing 48% Rh. Neutron diffraction study of this alloy gave μFeI=3.2 μB, but no direct measurement is available for μFeII. It is suggested that FeII, which is surrounded by 8 Fe nearest neighbors, may have a smaller magnetic moment than FeI despite its higher hyperfine field. The alloy with 50% Rh transforms, on cooling, from ferromagnetic to antiferromagnetic at 65^∘{}C. At this phase transition the hyperfine field shows a discontinuous decrease of 14 kOe.