Grain Growth Effect of Cr $_{2}$ O $_{3}$ Thin Film Layer on Exchange Coupling of Cr

We have observed high exchange bias for a Cr₂O₃ film, which was crystallized from an amorphous Cr-oxide by annealing in O₂ flow. To clarify the origin of the high exchange bias, we characterized the morphology of the Cr₂O₃ film. From X-ray diffraction, atomic force microscopy, and transmission electron microscopy measurements, we discovered that our polycrystalline Cr₂O₃ film was found to grow not to be entirely random orientation, but to form large R-planes on the surface. That is, R-planes were self-organized during crystallization. Since uncompensated Cr spins exist on R-planes of Cr₂O₃, the origin of the high exchange bias would be the self-organized R-planes. We successfully explained the peculiar temperature-dependent exchange bias and coercivity of the Cr₂O₃ film. For the Cr₂O₃ film, perpendicular exchange bias was obtained whereas out of plane direction is hard magnetization axis. This is because of the oblique Cr spin directions from out of plane direction of the film. The results demonstrated that exchange bias higher than coercivity (μ₀H_ex ≫ μ₀H_c) was realized near room temperature.