Observation of perpendicular exchange bias in an Ir-doped Fe₂O₃/Co ultrathin film system

In this work, we investigated the temperature dependence of interface exchange coupling in an Ir-doped Fe₂O₃/Co system with variations in the Ir-Fe₂O₃ thickness. Low-temperature perpendicular exchange bias was observed in the samples with an Ir-Fe₂O₃ thickness of 5 nm or less, when it cooled from 360 K in an external magnetic field of 1 T perpendicular to the sample surface. For 5 nm-thick Ir-Fe₂O₃, a maximum exchange bias value of 1200 Oe was obtained at 200 K. This is the first report on perpendicular exchange bias of an Fe₂O₃ thin film coupled with a ferromagnet. Enhancements to the Morin temperature and the magnetic anisotropy of Fe₂O₃ caused by lattice strain, Ir doping, and the finite-size scaling effect, as well as the high quality (good crystal orientation, small roughness, etc.) of the Fe₂O₃ film fabricated by our process, are considered to be mostly responsible for the perpendicular exchange bias obtained.