SPIN-POLARIZED EELS OF SURFACES

The spin dependence of electron energy loss processes in Ni is studied in detail by spin polarized electron energy loss spectroscopy (SPEELS). Exchange scattering plays a dominant role for small energy losses with a large contribution due to Stoner excitations. The angle and energy dependence of spin asymmetries can be described by the superposition of nearly isotropic impact scattering and largely spin independent dipole losses, strongly peaked around specular. The absence of a significant temperature dependence in the spin asymmetry spectrum is consistent with the persistence of local magnetic moments and a spin-split electronic structure at (and above) TC. It is suggested that the observed spin asymmetries give rise to a spin-dependent electron mean-free-path at low energies and play a role in the spin polarization enhancement and the surface sensitivity of low-energy secondary electrons. © 1990.