Solid-state synthesis, magnetic and structural properties of interfacial B2-FeRh(001) layers in Rh/Fe(001) films

Here we first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C. For all bilayers the non-magnetic nanocrystalline phase with a B2 structure (nfm-B2) is the first phase that is formed on the Rh/Fe(001) interface near 100 °C. Above 300 °C, without changing the nanocrystalline B2 structure, the phase grows into the low-magnetization modification α_l' (M_S^l ~ 825 emu/cm³) of the ferromagnetic α^' phase which has a reversible α_l' ↔ α" transition. After annealing 52Rh/48Fe(001) bilayers above 600 °C the α_l' phase increases in grain size and either develops into α_h' with high magnetization (M_S^h ~ 1,220 emu/cm³) or remains in the α_l' phase. In contrast to α_l', the α_h' ↔ α" transition in the α_h' films is completely suppressed. When the annealing temperature of the 45Rh/55Fe(001) samples is increased from 450 to 800 °C the low-magnetization nanocrystalline α_l' films develop into high crystalline perfection epitaxial α_h'(001) layers, which have a high magnetization of ~ 1,275 emu/cm³. α_h'(001) films do not undergo a transition to an antiferromagnetic α" phase. In 68Rh/32Fe(001) samples above 500 °C non-magnetic epitaxial γ(001) layers grow on the Fe(001) interface as a result of the solid-state reaction between the epitaxial α_l'(001) and polycrystalline Rh films. Our results demonstrate not only the complex nature of chemical interactions at the low-temperature synthesis of the nfm-B2 and α_l' phases in Rh/Fe(001) bilayers, but also establish their continuous link with chemical mechanisms underlying reversible α_l' ↔ α" transitions.