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Submicron ferromagnets have been successfully incorporated into semi-insulating (001) GaAs crystals by Mn+ ion implantation and subsequent rapid annealing. Magnetization measurements reveal room-temperature ferromagnetism. The structural and compositional properties of crystallites have been analyzed by transmission electron microscopy, energy dispersion x-ray spectrum, and electron microdiffraction. The results show that crystallites of MnGa and MnAs with a small amount of Ga are formed. Atomic force microscopy and magnetic force microscopy images indicate that the single-domain magnetic state is dominant in submicron ferromagnets under our annealing conditions (750 °C–900 °C).

The Faraday rotation as a function of photon energy for Cd1−xGdxTe with x=0.012 and 0.030 in the temperature range of 85–300 K has been measured. The Verdet constant includes a positive part and negative part due to pure Zeeman and sp-f exchange interaction contributions, respectively. The sp-f exchange interaction parameter has been determined in Cd1−xGdxTe: (q=9.3×10−4 at 85 K and q=5.3×10−4 at 300 K) in terms of a microscopic model, which takes into account the k dependence of the spin-spin exchange interaction. The normalization parameter C has been found to be independent of both the compositions of Gd and temperature. The agreement between the data and the microscopic model is very good in the whole spectra region even far from the band gap.

The effective interband g factors γΓ and γL at the Γ and L points of the Brillouin zone for Cd1−xFexTe with x=0.01 and 0.04 have been determined in the temperature range of 70–300 K from Faraday rotation measurements. The results show that the dominant contribution to γΓ is due to the sp–d exchange interaction between Fe2+ ions and free carriers, while the intrinsic contribution is dominant for γL. The exchange interaction integral N0(β−α) at the Γ point has also been obtained.

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