Probing Magnons by Spin-Polarized Electrons

High wave-vector magnon excitations in itinerant ferromagnets can be investigated by electron scattering experiments. In such an experiment, a spin-polarized beam with a well-defined energy is scattered from the sample surface and the energy distribution of the scattered electrons is measured. Since magnons possess a total angular momentum of 1(h)Over bar, they can only be excited (annihilated) by incidence of minority (majority) electrons. This fact leads to a peak in the energy loss (gain) region of the intensity spectra when minority (majority) electrons are incident. The scattering itself is elastic and the observed energy loss (or gain) is due to the fact that the ejected electron stems from a lower (or higher) energy level of the excited solid. Such a process is mediated by exchange interaction that is of a pure Coulomb nature and no explicit spin spin interaction is involved. We review the recent experimental attempts to probe and investigate the high wave-vector magnons in ultrathin ferromagnetic films by using spin-polarized electrons. Experimental results obtained by spin-polarized electron energy loss spectroscopy will be presented. The focus will be on the basic concepts and the nature of the different types of excitations probed by electrons. A possibility to distinguish between magnon- and phonon-excitations without the need of spin selective detection will be discussed.