THEORY OF SPIN-WAVE SPECTRA IN HEUSLER ALLOYS

The spin wave spectra of three Heusler alloys (X2MnZ) measured by Ishikawa et al have been analysed by means of a model containing the three magnetic interactions which we believe are present in these materials: Coulomb exchange between localized dl and itinerant di electrons, s-dl exchange, and superexchange via the Z atoms. Reasonable fits to the data were obtained in which the main variation between alloys was a differing di-dl interaction representing the change in di electron density as X is varied. This di-dl interaction dominates the first three near-neighbor exchange parameters and appears to be responsible for ferromagnetism in these alloys.