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We investigated the effect of Al doping on the perpendicular exchange bias in Cr2O3/Co thin film systems. By Al doping, a large unidirectional anisotropy energy (J K ~ 0.74 erg/cm2) and a high blocking temperature (T B) were obtained simultaneously. The variations in J K and T B induced by Al doping were discussed on the basis of Mauri's model and explained from an increase in magnetic anisotropy and a decrease in the exchange stiffness constant of Cr2O3. Our first-principles calculations suggest a factor to improve the magnetic anisotropy of Cr2O3 markedly, which is different from the previously established lattice strain effect.

The electric control of surface magnetism is important for spintronic applications. Due to the screening of electric field by conduction electrons in metals, an electric field can be applied only at a surface layer. However, the electric field can be applied on metallic contacts smaller than the electron's mean free path. We report on the electric modulation of the phase-transition temperature of CoO that is present at Co/Pt nano-contacts through a thin AlO x barrier. We found a 50-K/V change that can be attributed to the injection of electrons through nano-contacts.

We experimentally investigated the asymmetric transmission probabilities of spin-up and spin-down electrons at a (001)-Fe/Ag interface, which result in a highly spin-dependent interface resistance () that improves the magnetoresistive outputs of giant magnetoresistive devices whose ferromagnetic layers comprise only 3d transitional materials such as FeCo-based alloys. We quantitatively determined the spin-dependent interfacial parameters at FexCo100-x/Ag interfaces that were tuned by varying the Fe concentration x. Among the interfaces, the highest interface resistance of 0.65 mΩµm2 was obtained with an of 1.89 mΩµm2, which corresponds to ARF/N↑ ~ 1.08 mΩµm2 and ARF/N↓ ~ 7.98 mΩµm2 at a (001)-Fe/Ag interface.

A ()-oriented Cr2O3 film was prepared, and the in-plane angular dependence of both its exchange bias (Hex) and blocking temperature (TB) were investigated. By changing the applied magnetic field direction, we modulated the relative angle between the magnetic anisotropy direction of Cr2O3 and the applied magnetic field direction. We found that TB ~ Neel temperature (TN) for a sufficiently large relative angle, while TB is smaller than TN for a small relative angle, reflecting a change in the effective exchange coupling energy. By tuning the applied magnetic field direction, we demonstrated extrinsic control of Hex and TB.

Spin torque oscillations near zero magnetic fields were investigated in a nanocontact magnetoresistive device. A typical auto-oscillation mode was observed with high amplitude and narrow linewidth in a vortex domain state of the free layer around the zero field. The number of branches was reduced to a single one with an increase of current over the threshold value. As a result, we observed a linear frequency change between a wider field range across zero fields with a high amplitude and a narrow linewidth for the oscillation. The frequency response to small bipolar applied fields is applicable to a weak-field sensor.