Magnetic spin excitations in diluted ferromagnetic systems: the case of
arXiv:cond-mat/0610465 · doi:10.1209/0295-5075/79/57007
Abstract
We propose a theory which allow to calculate the magnetic excitation spectrum in diluted ferromagnetic systems. The approach is rather general and based on the Self-Consistent local Random Phase Approximation in which disorder (dilution) and thermal fluctuations are properly treated. To illustrate its reliability and accuracy we calculate the magnetic excitation in the diluted III-V magnetic semiconductor . It is shown that dilution has a drastic effect on the excitation spectrum, indeed well defined magnon excitations exist only in a small region of the Brillouin zone centered around the point. We also calculate the spin stiffness in optimally annealed sample as a function of concentration. A comparison to available measurements is done. We find a very good agreement for both the Curie temperature and the spin stiffness measured in well annealed samples and provide a plausible explanation for the very small values measured in as grown samples.
The manuscript has been modified, 4 figures are included. Accepted for publication in Eur. Phys. Lett