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 degrees 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 degrees C. Above 300 degrees C, without changing the nanocrystalline B2 structure, the phase grows into the low-magnetization modification alpha(l)' (M(S)(l similar to)825 emu/cm(3)) of the ferromagnetic alpha(') phase which has a reversible alpha(l)'<->alpha transition. After annealing 52Rh/48Fe(001) bilayers above 600 degrees C the alpha(l)' phase increases in grain size and either develops into alpha(h)' with high magnetization (M(S)(h similar to)1,220 emu/cm(3)) or remains in the alpha(l)' phase. In contrast to alpha(l)', the alpha(h)'<->alpha transition in the alpha(h)' films is completely suppressed. When the annealing temperature of the 45Rh/55Fe(001) samples is increased from 450 to 800 degrees C the low-magnetization nanocrystalline alpha(l)' films develop into high crystalline perfection epitaxial alpha(h)'(001) layers, which have a high magnetization of similar to 1,275 emu/cm(3). alpha(h)'(001) films do not undergo a transition to an antiferromagnetic alpha phase. In 68Rh/32Fe(001) samples above 500 degrees C non-magnetic epitaxial gamma(001) layers grow on the Fe(001) interface as a result of the solid-state reaction between the epitaxial alpha(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 alpha(l)' phases in Rh/Fe(001) bilayers, but also establish their continuous link with chemical mechanisms underlying reversible alpha(l)'<->alpha transitions.