Spin wave excitations in iron by spin-polarized electrons

For the last two decades, spin polarized electron energy loss spectroscopy (SPEELS) has been instrumental in the investigation of Stoner excitations in ferromagnets. Collective spin excitations, on the other hand, have only recently been detected by this technique. In this study, SPEELS was used to investigate spin wave excitations in both bulk Fe films as well as in ultra-thin Fe films of just one or two layers.; The spectrometer that was constructed for this work was a 127 degree cylindrical deflector with an analyzer rotatable through 90 degrees. The polarized electron beam was produced by a negative electron affinity GaAs photocathode. Data were taken with primary beam energies that varied between 20 and 8 eV at resolutions between 75 and 25 meV FWHM. Spin asymmetries show the Stoner continuum as noted in the previously conducted SPEELS experiments as well as an additional feature lower in energy loss due to the excitation of spin waves.; Spin asymmetries of thick Fe/GaAs(100) films show a broad energy loss peak centered at 165 meV. The spin wave lineshape is clearly asymmetric with sharp onset and a gently sloping tail. This asymmetry is attributed to the excitation of a continuum of bulk spin waves due to non-conservation of perpendicular momentum in the scattering process.; Spectra of ultra-thin Fe films grown on Ag(100) also show the presence of spin excitations at low energy loss. Data are presented that show variation of spin wave position based on film thickness. In addition, unlike the single broad spin wave observed in the thick Fe films, thin films of two layers were seen to exhibit two discrete peaks corresponding to standing wave modes.