Low-frequency spin dynamics in diluted magnetic semiconductors

Abstract

The low-frequency dynamical magnetic properties in paramagnetic diluted magnetic semiconductors are addressed in the framework of the dynamical mean-field theory applied for the Kondo lattice model. In the infinite-dimensional limit, a set of self-consistent equations is derived so the single-particle Green's function and its self-energy can be evaluated numerically. In terms of the Green's function and self-energies, the local dynamical spin susceptibility function and then the spin-relaxation rate are explicitly expressed based on the Baym-Kadanoff approach. It is found that the spin fluctuations become dominated, indicated by the sharp peak appearing at the low frequency of the spin dynamical susceptibility function in the case of large magnetic coupling and temperature close to the paramagnetic-ferromagnetic transition point. The low-frequency spin dynamic in the systems is also addressed in the signatures of the spin-relaxation process. In the case of large temperature and small magnetic coupling, the spin-relaxation rate releases the scenario of the Korringa process specifying the weak correlation systems likely normal metals. Otherwise, i.e., at small temperature and large magnetic coupling, we find exponential behavior of the spin-relaxation rate versus temperature. Moreover, at a temperature approaching the paramagnetic-ferromagnetic transition point, one finds sharp suppression of the spin-relaxation rate or speeding up of the spin-relaxation time. These scenarios are attributed to the appearance of the magnetic coherence bound state or the spin clusters in diluted magnetic semiconductors due to the strongly magnetic correlations.