Elastic versus inelastic spin-polarized electron scattering from a ferromagnetic surface

Abstract

Spin-polarized electron energy loss spectroscopy was applied to study the intensity asymmetry upon the reversal of the incident spin polarization of elastically and inelastically scattered polarized electrons from an epitaxial ferromagnetic Fe layer on W(110). The polarization of the incident beam was always collinear with the magnetic moment (magnetization) of the sample, and the asymmetries were measured for two opposite magnetizations of the sample. They allowed extracting the exchange and the spin-orbit components from the measured asymmetry. A strong asymmetry of Stoner excitations in an Fe film on W(110) is observed, as expected, at about 3 eV energy loss. The value of the asymmetry declines but is still observable when the surface is contaminated. The asymmetry of elastic scattering for normal incidence and a 50\ifmmode^\circ\else\textdegree\fi{} detection angle is close to zero in contrast to the Stoner excitation asymmetry (inelastic scattering). However, the asymmetry of elastic scattering increases substantially at two specular geometries with 25\ifmmode^\circ\else\textdegree\fi{} and 72\ifmmode^\circ\else\textdegree\fi{} angles of incidence, compared to the normal incidence, and may be even larger than the asymmetry of Stoner excitations. The sign of elastic scattering asymmetry changes upon the reversal of the sample magnetization, indicating the magnetic origin of this asymmetry, i.e., spin-dependent electron-electron scattering with electron exchange. The calculation of the asymmetry of elastic spin-polarized electron scattering from a spin-dependent surface potential barrier shows a qualitative agreement with the measurements.