Screening, Instability of the Uniform State, and Charge Carrier Scattering in Heavily Doped Ferromagnetic Semiconductors

Abstract

A calculation of the static dielectric function ε(q) and the magnetic response function to an electrostatic perturbation χ(q) is carried out for heavily doped ferromagnetic semiconductors. Due to the spin polarization of the charge carrier a strong correlation exists between the fluctuations of electron density and magnetization. This leads to diminishing screening length and the appearance of local magnetic moments near impurities, which, in turn, causes a strong magnetic field and temperature dependence of the resistivity. On further temperature increase, the screened potential becomes oscillating, and the screening length increases, going to infinity at a temperature which corresponds to the absolute instability of the uniform state. But still earlier a first order phase transition should occur into a nonuniform state, the nonuniform state being metastable in some temperature range. It may be responsible for the resistivity hysteresis observed in some ferromagnetic semiconductors.