Determination of specific ion positions of Cr3+ and O2− in Cr2O3 thin films and their relationship to exchange anisotropy at Co/Cr2O3 interfaces

Abstract

The structures of antiferromagnetic Cr2O3(0001) thin films with perpendicular exchange bias were investigated using reflection high-energy electron diffraction, X-ray reflectivity, and synchrotron X-ray diffraction. We mainly investigated the specific ion positions of Cr3+ and O2− in the corundum structure and discussed their relationship to the magnetic anisotropy of Cr2O3. The Cr2O3(0001) thin film grown on a Pt(111) buffer layer exhibited a perpendicular exchange anisotropy density of 0.42 mJ/m2, in which the Cr3+ position is the primary factor in the enhancement of magnetic anisotropy due to dipolar-interaction. In contrast, the single-crystalline Cr2O3(0001) film grown on a α-Al2O3(0001) substrate featured a low exchange magnetic anisotropy of 0.098 mJ/m2. In this film, the Cr3+ position parameter is an insignificant factor, leading to low magnetic anisotropy. The O2− ion position also differs between the two types of films, which can affect both the magnetic anisotropy energy originating from fine structures and the magneto-electric properties of Cr2O3.