AVS 49th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeA

Paper MI-WeA5
Spin Wave Excitations by Low Energy Electrons in Fe

Wednesday, November 6, 2002, 3:20 pm, Room C-205

Session: Magnetization Dynamics
Presenter: M.R. Vernoy, University of California, Irvine
Authors: M.R. Vernoy, University of California, Irvine
H. Hopster, University of California, Irvine
D.L. Mills, University of California, Irvine
Correspondent: Click to Email
A new spectrometer for spin polarized electron energy loss spectroscopy (SPEELS) has been constructed. The spectrometer is based on 127° cylindrical sectors as monochromator and analyzer, with the analyzer being rotatable for angle dependent measurements. A standard GaAs negative-electron-affinity photoemitter source is coupled to the monochromator and provides spin polarized electrons with polarization values around 25 %. SPEELS measurements were performed on thick (several 100 Å) epitaxial Fe films grown in situ on GaAs(100) substrates. The Fe films were remanently magnetized by a magnetic field pulse and SPEELS spectra were taken with the incoming beam polarization parallel or antiparallel to the magnetization. The primary energy used was 20 eV and an energy resolution of 25 meV (FWHM) was achieved. Strong spin asymmetries are detected in the energy loss spectrum. In addition to the well known Stoner excitation spectrum at high energies there is a distinct loss structure at small energies (100-300 meV) due to spin wave excitations. This spin wave energy loss structure has a highly asymmetric shape with a sharp onset around 100 meV, a maximum around 165 meV and a tail extending out to 350 meV. This peak shape can be explained by excitation of a continuum of bulk spin waves due to the non-conservation of q-perpendicular in the excitation process. We shall present comparison between the measured spectra and model calculations which employ a very simple description of the excitation process, and a Heisenberg model to describe spin waves at the crystal surface.