Ferromagnetism at the interfaces of antiferromagnetic FeRh epilayers

Abstract

The nanoscale magnetic structure of FeRh epilayers has been studied by polarized neutron reflectometry. Epitaxial films with a nominal thickness of 500 A were grown on MgO 001 substrates via molecular-beam epitaxy and capped with 20 A of MgO. The FeRh films show a clear transition from the antiferromagnetic AF state to the ferromagnetic FM state with increasing temperature. Surprisingly the films possess a FM moment even at a temperature 80 K below the AF-FM transition temperature of the film. We have quantified the magnitude and spatial extent of this FM moment, which is confined to within 60‐80 A of the FeRh near the top and bottom interfaces. These interfacial FM layers account for the unusual effects previously observed in films with thickness 100 A. Given the delicate energy balance between the AF and FM ground states we suggest a metastable FM state resides near to the interface within an AF matrix. The length scale over which the FM region resides is consistent with the strained regions of the film.