The magnetic coupling at the interface of Co and Cr has been investigated using ultrathin Co film on Cr 2 O 3 ͑0001͒ film, which is expected to be a promising system to show the magnetoelectronic effect. We mainly examined the temperature dependence of magnetization, the exchange bias at different field directions relative to the Cr spin direction, and the temperature dependence of exchange bias. The temperature dependence of magnetization under 50 Oe indicates the collinear coupling of Co spin and Cr spin at the interface. Furthermore, the exchange bias effect is observed in the coupled direction of Co and Cr, namely, parallel to the Cr spin direction. However, the changes in the magnetic behavior with changing field directions and Co thicknesses imply the existence of biquadratic coupling of Co spin and Cr spin, as well. In agreement with the numerical calculation under the coexistence of collinear and biquadratic couplings, the exchange bias field decreases nonmonotonically with increasing temperature.

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We have investigated the perpendicular magnetic anisotropy (PMA) at the ferromagnetic/antiferromagnetic interface using [Pt/Co]n/α-Cr2O3 superlattices. By changing the number of stacking periods, the contributions of the Co/α-Cr2O3 and Pt/Co interfaces to the PMA are separately estimated. The results indicate that the strong PMA is induced at the Co/α-Cr2O3 interface as well as at the Pt/Co interface. The change in the interface magnetic anisotropy energy density with the ferromagnetic layer composition supports the PMA at the Co/α-Cr2O3 interface. To the best of our knowledge, this is the first demonstration of PMA at the ferromagnetic/antiferromagnetic interface.

We have investigated the fabrication of α-Cr2O3(0001) thin film on a Au(111) surface and the effect of the antiferromagnetic feature of α-Cr2O3(0001) on the magnetic properties of ultrathin Co film on α-Cr2O3(0001). Highly oriented α-Cr2O3(0001) thin film is fabricated by oxidizing Cr(110) thin film grown on a Au (111) surface. Upon the oxidization of threefold symmetric Cr(110) thin film, the α-Cr2O3(0001) thin film is produced. On α-Cr2O3(0001) thin film, ultrathin Co film is epitaxially grown at 473 K to form fcc-Co(111) film. The antiferromagnetic feature of α-Cr2O3 affects the magnetic properties of the ultrathin Co film. Exchange bias is only observed when the magnetic field is applied perpendicular to the film surface, i.e., the direction parallel to the Cr spin. Additionally, in the temperature dependence of magnetization, the clear signature of a Néel temperature of approximately 300 K is observed. The obtained results indicate the collinear coupling of Co and Cr spins.

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