Domain state exchange bias in a single layer FeRh thin film formed via low energy ion implantation

Abstract

Modern spintronics relies heavily on the exchange bias effect to pin the orientation of ferromagnetic layers in magnetic tunnel junctions. The current implementations of exchange bias in magnetic tunnel junctions employ pristine interfaces between antiferromagnetic and ferromagnetic layers. Here we reveal an interfacial exchange bias introduced by a single-step, low-energy ion implantation process in a single layer FeRh thin film. Both 1 keV He⁺ ions and 5 keV Fe⁺ were investigated, their energy selected to ensure the ions would stop within the FeRh film. The ions reduce the metamagnetic transition temperature through defect generation to form a surface layer with ferromagnetic ordering. Temperature dependent magnetism measurements reveal a room temperature exchange bias between the ferromagnetic surface and the antiferromagnetic bulk of ∼41 Oe in 5 keV Fe⁺ implanted samples and ∼36 Oe for 1 keV He⁺ implanted samples. We directly scrutinize this exchange bias effect in magnetic depth profiles obtained by polarized neutron reflectometry which clearly show a pinned ferromagnetic layer adjacent to the disordered layer created by low energy Fe⁺ ion implantation. These results reveal a novel method to implement exchange bias in an antiferromagnetic layer that can have direct application in the field of spintronics.