Interface effects of polycrystalline Fe₂O₃ thin films on Pt

The magnetic state of an antiferromagnetic (AFM) insulator can be read and manipulated in spintronics devices using bilayers of an AFM and a conducting layer, making it useful for spintronics devices. To date, research has focused on single crystals of AFMs, which enables the study of properties related to different crystallographic surfaces. However, combining single-crystal AFMs in spintronics devices may be problematic due to substrate selectivity and deposition conditions. In this work, we study the properties of polycrystalline Fe₂O₃ coupled with Pt as the conducting layer, asking how the magnetoresistive behavior differs in polycrystalline AFMs. We report on the angle dependent magnetoresistance and transverse magnetoresistance properties as a function of temperature and magnetic fields, comparing Fe₂O₃/Pt and Fe₂O₃/Cu/Pt thin films, in addition to magnetometry and structural characterization. The magnetoresistance signals do not depend on the thickness or volume behavior of the Fe₂O₃ layer, but rather the Fe₂O₃/Pt interface. Angle dependent magnetoresistance measurements show ferromagnetic-like behavior but with a non-standard effect of field, while transverse measurements show a sign change with temperature. This differs from effects reported for single-crystal Fe₂O₃ based bilayers. Interestingly, using transverse field measurements, we find that at low temperatures, the Fe₂O₃/Pt interface spins develop a glass-like relaxation of the magnetic signal, which undergoes freezing as the sample is further cooled.