Title: FERROMAGNETIC TRANSITION IN DILUTED MAGNETIC SEMICONDUCTORS
Authors: T.Dietl (Institute of Physics and College of Science, Polish Academy of Sciences al. Lotnikow 32/46, PL-02668 Warszawa, Poland)

A summary is given of recent theoretical works on effects of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the localized spins in various dimensionality systems of doped diluted magnetic semiconductors (DMS). Since this interaction is long-range, its influence on the temperature and magnetic field dependencies of magnetization and spin splitting of the bands is evaluated in the mean field approximation, but by taking into consideration disorder-modified carrier-carrier interactions. Theoretical evaluations show that the hole densities, which can presently be achieved, are sufficiently high to drive a paramagnetic-ferromagnetic phase transition in bulk and modulation-doped structures of II-VI DMS. The results of recent magnetooptical studies on MBE-grown samples, containing a single, modulation-doped, 8 nm quantum well of Cd$_{1-x}$Mn$_{x}$Te/Cd$_{1-y-z}$Mg$_{y}$Zn$_{z}$Te:N are shown to corroborate the theoretical expectations. These studies reveal the presence of a ferromagnetic transition induced by the two-dimensional hole gas. The transition occurs between 1.8 and 2.5 K, depending on the Mn concentration $x$, in agreement with the theoretical model.

Comments: Figs. 2, Refs. 50, Tabs. 0.