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.