Collective spin fluctuations in diluted magnetic semiconductors

We investigate collective spin fluctuations in ferromagnetic (III, Mn)V semiconductors. Our analysis is based on a model with kinetic-exchange coupling between localized Mn spins and valence-band carriers. We derive an independent spin-wave theory to determine the spin-wave spectrum and extract the spin stiffness. Differences between a two-band and a more sophisticated six-band model for the valence-band carriers are discussed. We use these results and Monte-Carlo simulations to demonstrate that collective fluctuations, neglected by mean-field theory, become increasingly important in limiting the Curie temperature when the density of states is large.