Enhanced B2 Ordering of FeRh Thin Films Using B2 NiAl Underlayers

B2-ordered FeRh thin films undergo a first-order magnetic transition from an antiferromagnetic (AFM) state at low temperature to a ferromagnetic (FM) state above 350 K and reverse back on cooling with a finite hysteresis. This property makes them very attractive for use in temperature-controlled exchange coupling layers for heat-assisted magnetic recording. In order to be used as an exchange coupling layer, the goal is to fabricate ultra-thin films of FeRh that show reversible AFM-FM switching. For thinner films grown on MgO substrates, there exists an FM signal below the AFM-FM transition temperature. It is demonstrated that there is a direct correlation between the low-temperature FM fraction and the extent of atomic ordering. Based on this observation, the enhanced atomic order in FeRh grown on NiAl underlayers is shown to result in bulk-like AFM-FM switching, especially for the thinner films.