The magnetic and magneto-optical properties of a Cr-doped II-VI semiconductor ZnTe were investigated. Magnetic circular dichroism measurements showed a strong interaction between the sp carriers and localized d spins, indicating that Zn(1-x)Cr(x)Te is a diluted magnetic semiconductor. The Curie temperature of the film with x=0.20 was estimated to be 300+/-10 K, which is the highest value ever reported for a diluted magnetic semiconductor in which sp-d interactions were confirmed. In spite of its high Curie temperature, Zn(1-x)Cr(x)Te film shows semiconducting electrical transport properties.

We study the voltage control of perpendicular magnetic anisotropy in an ultrathin Fe layer sandwiched between the Cr buffer and MgO tunneling barrier layers. A high-interface magnetic anisotropy energy of 2.1 mJ=m 2 is achieved in the Cr/ultrathin Fe=MgO structure. A large voltage-induced perpendicular magnetic anisotropy change is observed under the negative-bias voltage applications for the case of the Fe layer thinner than 0.6 nm. The amplitude of the voltage-induced anisotropy energy change exhibits a strong Fe-thickness dependence and it reaches as high as 290 fJ=Vm. The observed high values of the surface anisotropy and voltage-induced anisotropy energy change demonstrate the feasibility of voltage-driven spintronic devices.

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Highly Cr-doped II-VI diluted magnetic semiconductor ͑DMS͒ Zn 1Ϫx Cr x Te films with a ferromagnetic long-range order have been grown. A phase diagram of Zn 1Ϫx Cr x Te in relation to the growth temperature and Cr concentration was determined. Magnetic circular dichroism measurements revealed that a magnetically single phase of DMS Zn 1Ϫx Cr x Te is obtained in the films with Cr concentration up to xϭ0.20. Spontaneous magnetization of the film with xϭ0.20 disappears around 300 K, indicating that the Zn 1Ϫx Cr x Te is a DMS with room-temperature ferromagnetism.

The electronic structure of a prototype dilute magnetic semiconductor (DMS), Ga(1-x)MnxAs, is studied by magnetic circular dichroism (MCD) spectroscopy. We prove that the optical transitions originated from impurity bands cause the strong positive MCD background. The MCD signal due to the E0 transition from the valence band to the conduction band is negative indicating that the p-d exchange interactions between the p carriers and d spin is antiferromagnetic. The negative E0 MCD signal also indicates that the hole doping of the valence band is not so large as previously assumed. The impurity bands seem to play important roles for the ferromagnetism of Ga(1-x)MnxAs.