Inelastic Scattering of Slow Electrons from a Heisenfoerg Ferromagnet

The magnetic inelastic scattering of low-energy electrons by the (001) surface of a b.c.c. Heisenberg ferromagnet is considered. As a first step, the spectrum of elementary magnetic excitations is obtained, revealing the existence of optical and acoustic surface magnons, as well as a continuum of bulk magnons. The differential cross-section for inelastic scattering shows the contribution of those types of excitations; localized niagnons give a delta function contribution, while the contribution due to the bulk states is qualitatively different depending on the value of the ratio of the exchange integrals for surface and bulk spins, thereby providing a method for investigating the exchange interactions at the surface. On considers la dispersion magnetique inelastique des electrons de basee energie, par la surface (001) d'un cristal b.c.c. ferromagnetique, dans le modele de Heisenberg. D'abord on calcule le spectre des excitations magnetiques elementaires qui montre l'existence de magnons superficiels acoustiques et optiques, et une bande de magnons de volume. La section efficace de dispersion inelastique presente la contribution de toutes cettes excitations. La contribution des magnons localises est une function delta. La valeur de la relation J′/J de l'integral d'exchange J′ pour spins de la surface et J pour spins dans le volume, determine des contributions qualitativement differentes des etats de volume, selon le cas. Alors, on a la possibilitye d'etudier les interactions d'exchange dans la surface.