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 ${\mathrm{Z}\mathrm{n}}_{1-x}{\mathrm{C}\mathrm{r}}_x\mathrm{T}\mathrm{e}$ is a diluted magnetic semiconductor. The Curie temperature of the film with $x=0.20$ was estimated to be $300\pm 10\mathrm{K}$, which is the highest value ever reported for a diluted magnetic semiconductor in which $sp\mathrm{\text{−}}d$ interactions were confirmed. In spite of its high Curie temperature, ${\mathrm{Z}\mathrm{n}}_{1-x}{\mathrm{C}\mathrm{r}}_x\mathrm{T}\mathrm{e}$ 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 $2.1\mathrm{mJ}/{\mathrm{m}}^2$ is achieved in the Cr/ultrathin $\mathrm{Fe}/\mathrm{MgO}$ 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 $290\mathrm{fJ}/\mathrm{Vm}$. The observed high values of the surface anisotropy and voltage-induced anisotropy energy change demonstrate the feasibility of voltage-driven spintronic devices.

The electronic structure of a prototype dilute magnetic semiconductor (DMS), ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$, 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 $E_0$ transition from the valence band to the conduction band is negative indicating that the $p\mathrm{\text{−}}d$ exchange interactions between the $p$ carriers and $d$ spin is antiferromagnetic. The negative $E_0$ 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 ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$.

Epitaxial films of ${\mathrm{Zn}}_{1-x}{\mathrm{Cr}}_x\mathrm{Te}$ were grown on a GaAs substrate. The lattice constant of ${\mathrm{Zn}}_{1-x}{\mathrm{Cr}}_x\mathrm{Te}$ follows Vegard’s law, meaning that Cr ions replace Zn sites in the host lattice. A strong enhancement of the magnetic circular dichroism (MCD) signals was observed near the optical transition energies corresponding to the critical points of the host ZnTe. This indicates that ${\mathrm{Zn}}_{1-x}{\mathrm{Cr}}_x\mathrm{Te}$ is a diluted magnetic semiconductor with a strong sp-d mixing. The magnetic-field dependence of the MCD signals showed that the observed ferromagnetic hysteresis loop comes from ${\mathrm{Zn}}_{1-x}{\mathrm{Cr}}_x\mathrm{Te}.$

Highly Cr-doped II–VI diluted magnetic semiconductor (DMS) Zn1−xCrxTe films with a ferromagnetic long-range order have been grown. A phase diagram of Zn1−xCrxTe in relation to the growth temperature and Cr concentration was determined. Magnetic circular dichroism measurements revealed that a magnetically single phase of DMS Zn1−xCrxTe is obtained in the films with Cr concentration up to x=0.20. Spontaneous magnetization of the film with x=0.20 disappears around 300 K, indicating that the Zn1−xCrxTe is a DMS with room-temperature ferromagnetism.