Spin excitations of a model itinerant ferromagnetic film: Spin waves, Stoner excitations, and spin-polarized electron-energy-loss spectroscopy

Publisher Website
Google Scholar
Abstract
We discuss the spin excitations of a simple model of an ultrathin ferromagnetic film, in which the magnetic moment bearing electrons are itinerant in character. The one-band Hubbard model, treated in mean-field theory, forms the basis of the discussion. The spin excitations are treated by means of the random-phase approximation. We find spin-wave modes of standing wave character, and a spectrum of Stoner excitations influenced strongly by size effects. While the dispersion relations of the standing spin-wave modes appear as expected from a localized-spin model, there are substantive differences between the itinerant- and localized-spin cases. An example is the number of spin-wave modes evident in the appropriate spectral density functions, for each wave vector. We use a previously developed formalism of spin-polarized electron-energy-loss scattering (SPEELS) to compute SPEELS spectra for our model film. In addition to a broad feature with origin in Stoner excitations, we find clear and relatively intense spin-wave loss peaks.