Ferromagnetic transition and spin fluctuations in diluted magnetic semiconductors

Abstract

The magnetic properties over a wide range of temperatures in diluted magnetic semiconductors (DMSs) are discussed in the framework of the Kondo lattice model with magnetic impurity disorder. In the approach of dynamical mean-field theory, a set of self-consistent equations has been derived to specify single-particle Green functions. Analytical expressions of the static magnetic susceptibility and the ${B}_{1g}$ channel Raman response are then delivered. Inspecting for signatures of an itinerant carrier density of states and magnetization, we have identified a stable ferromagnetic (FM) state at low temperature. With increasing temperature, thermal fluctuations diminish the ordered state and the system favors a paramagnetic (PM) phase. Tracking and tracing different model parameters, the FM-PM transition phase diagram has been constructed. Spin fluctuations in the PM state have been pointed out in the behaviors of the self-energies, the static magnetic susceptibility, and the Raman scattering. Analyzing the properties of the ${B}_{1g}$ channel Raman response, we have attributed a formation of magnetic polarons in the PM state. The magnetic polaron scenario in a wide range of temperatures has been then intensively discussed. For the first time, both the static magnetic susceptibility and the ${B}_{1g}$ Raman response have been combined together to discuss the magnetic properties in DMSs compactly based on the dynamical mean-field approach.