We report a strong correlation between the location of Mn sites in ferromagnetic ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ measured by combined channeling Rutherford backscattering and by particle-induced x-ray emission experiments and its Curie temperature. The concentrations of free holes determined by electrochemical capacitance-voltage profiling and of uncompensated ${\mathrm{Mn}}^{2+}$ spins determined from superconducting quantum-interference device magnetization measurements are found to depend on the concentration of unstable defects involving highly mobile Mn interstitials. This leads to large variations in $T_C$ of ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ when it is annealed at different temperatures in a narrow temperature range. The fact that annealing under various conditions has failed to produce Curie temperatures above ∼110 K is attributed to the existence of an upper limit on the free hole concentration in low-temperature-grown ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}.$

Large, well-defined magnetic domains, on the scale of hundreds of micrometers, are observed in ${\mathrm{G}\mathrm{a}}_{1-x}{\mathrm{M}\mathrm{n}}_x\mathrm{A}\mathrm{s}$ epilayers using a high-resolution magneto-optical imaging technique. The orientations of the magnetic moments in the domains clearly show in-plane magnetic anisotropy, which changes through a second-order transition from a biaxial mode (easy axes nearly along [100] and [010]) at low temperatures to an unusual uniaxial mode (easy axis along [110]) as the temperature increases above about $T_c/2$. This transition is a result of the interplay between the natural cubic anisotropy of the GaMnAs zinc-blende structure and a uniaxial anisotropy which attribute to the effects of surface reconstruction.

A strong temperature and magnetic field dependence of conductivity has been found in ${\mathrm{Cd}}_{0.95}$ ${\mathrm{Mn}}_{0.05}$Se. The effect appears to result from the influence of magnetic polarons and of the exchange-induced spin splitting on the quantum corrections to the conductivity of disordered magnetic metals.

We report on optical properties of CdTe self-assembled quantum dots (SADs) grown by molecular beam epitaxy on ZnTe. Formation of SADs was achieved by deposition of 1.5–2.5 monolayers of CdTe at a substrate temperature of 420 °C and by applying growth interrupts for few seconds in Cd flux. The resulting dots have a typical diameter of 2 nm and a sheet density of ${10}^{12} {\mathrm{cm}}^{\text{−2}}.$ At T=2 K the photoluminescence (PL) spectra consist of two emission lines. The high-energy line originates from excitonic recombination in a wetting layer while the low-energy emission PL band is assigned to recombination in SADs. The increase in temperature up to 70 K does not affect the SADs-related emission intensity. It shifts, however, the PL peak energy towards low energies and causes a significant narrowing of the PL linewidth, from 80 meV at 1.9 K to 50 meV at 130 K. The activation energy of the thermal quenching of SADs-related PL emission was found to be equal to 47 meV. This value is three times greater than the one observed in CdTe/ZnTe quantum wells, that is, 12–17 meV.

We have fabricated (Ga,Mn)As nanostructures in which domain walls can be pinned by sub-10 nm constrictions. Controlled by shape anisotropy, we can switch the regions on either side of the constriction to either parallel or antiparallel magnetization. All samples exhibit a positive magnetoresistance, consistent with domain-wall trapping. For metallic samples, we find a magnetoresistance up to $8\%$, which can be understood from spin accumulation. In samples where, due to depletion at the constriction, a tunnel barrier is formed, we observe a magnetoresistance of up to $2000\%$.

The mechanisms for generation of long-lived spin coherence in a two-dimensional electron gas (2DEG) have been studied experimentally by means of a picosecond pump-probe Kerr rotation technique. $\mathrm{Cd}\mathrm{Te}∕(\mathrm{Cd},\mathrm{Mg})\mathrm{Te}$ quantum wells with a diluted 2DEG were investigated. The strong Coulomb interaction between electrons and holes, which results in large binding energies of neutral excitons and negatively charged excitons (trions), allows one to address selectively the exciton or trion states by resonant optical excitation. Different scenarios of spin coherence generation were analyzed theoretically, among them the direct trion photocreation, the formation of trions from photogenerated excitons, and the electron-exciton exchange scattering. Good agreement between experiment and theory is found.