Spin dynamics in (III,Mn)V ferromagnetic semiconductors: the role of correlations

TL;DR

This paper develops a comprehensive theory to analyze how correlations between spin and charge influence the dynamical properties of ferromagnetic semiconductors, revealing significant effects on spin stiffness and damping.

Contribution

It introduces a correlation expansion approach beyond RPA to accurately model quantum fluctuations in spin-charge coupled systems.

Findings

Correlations significantly modify spin stiffness.

Carrier concentration impacts magnetization damping.

Quantum fluctuations alter spin-wave spectra.

Abstract

We address the role of correlations between spin and charge degrees of freedom on the dynamical properties of ferromagnetic systems governed by the magnetic exchange interaction between itinerant and localized spins. For this we introduce a general theory that treats quantum fluctuations beyond the Random Phase Approximation based on a correlation expansion of the Green's function equations of motion. We calculate the spin susceptibility, spin--wave excitation spectrum, and magnetization precession damping. We find that correlations strongly affect the magnitude and carrier concentration dependence of the spin stiffness and magnetization Gilbert damping.