Atomic Spin Scattering and Giant Magnetoresistance in Magnetic Semiconductors

We studied electrical transport in dilute magnetic semiconductors, which is determined by scattering free carriers by localized magnetic moments. While calculating the scattering time and the mobility of the majority and minority-spin carriers, we took into account both the effects of thermal spin fluctuations and of the spatial disorder of magnetic atoms. These effects are responsible for the magnetic-field dependence of electrical resistivity. Namely, the application of the external magnetic field suppresses the thermodynamic spin fluctuations, thus promoting negative magnetoresistance (MR). Simultaneously, scattering by built-in spatial fluctuations of the atomic spins increases with the magnetic field. The latter effect is due to the growth of the magnitude of random local Zeeman splittings with the magnetic field. It promotes positive MR. We discuss the role of the above effects on MR of semiconductors where magnetic impurities are isoelectronic