Magnetic-field and temperature dependence of the photoinduced Faraday effect in diluted magnetic semiconductors

The photoinduced Faraday process in the diluted magnetic semiconductor ${\mathrm{Cd}}_{0.75}$ ${\mathrm{Mn}}_{0.25}$Te is investigated for laser frequencies well below the semiconductor band gap. This study is performed through measurement of the giant photoinduced rotations of the laser polarization as the magnetic field, laser intensity, and temperature are changed. We identify three different contributions for the photoinduced Faraday rotation angle: a fast Kerr contribution proportional to the laser intensity, a population change due to two-photon absorption and carrier stimulated recombination, and a ${\mathrm{Mn}}^{2+}$-ion magnetization as a consequence of the spin exchange interaction between the photocreated carriers and the magnetic ions. The last two contributions, which are quadratic in the laser intensity, saturate as the magnetic field increases, due to the saturation of the total spin of electrons and holes in the conduction and valence bands. An experimental study of the low-temperature dependence of the photoinduced Faraday rotation confirms the theoretical analysis and shows that the population and magnetic contributions are almost temperature independent while the Kerr term exhibits the same behavior as the linear Faraday rotation angle.