Abstract
By using an approach based on the Self-Consistent Local Random Phase Approximation (SC-LRPA) we calculate the magnetic excitation spectrum in diluted/disordered ferromagnetic systems. In previous studies, the SC-LRPA was shown to be reliable for the determination of the Curie temperature. In this letter, we now demonstrate its accuracy and efficiency for the determination of the magnetic excitation spectrum. For that purpose, we calculate the spin excitations of the widely studied diluted III-V magnetic semiconductor Ga1−xMnxAs. Instead of the expected broadening of the excitations due to disorder, it is shown that magnons exist only in a very restricted region of the Brillouin zone. We calculate without adjusting parameters, the spin stiffness in optimally annealed systems as a function of x and compare it to recent measurements. We find a very good agreement for well annealed samples and provide a plausible explanation for the very small values measured in as grown ones. We hope that this study will stimulate new studies as Ineslatic Neutron Scattering measurements for example.
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