Electron energy loss by electron-hole excitations in ferromagnets: The near-specular geometry

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Abstract
A low-energy electron which reflects off a crystal surface couples to particle-hole excitations through the Coulomb interaction. This leads to a contribution to the electron-energy-loss spectrum peaked about the specular direction. It is pointed out that if the material is a ferromagnet, a spin dependence of the near-specular loss spectrum occurs as a consequence of interference between the direct Coulomb matrix element, and the non-spin-flip portion of the exchange coupling of the incident electron to the particle-hole spectrum. It is suggested that this interference effect, and not spin-flip scattering, is responsible for the spin-dependent feature reported by Kirschner, Rebenstorff, and Ibach in their study of the near-specular electron-energy-loss spectrum of the Ni(110) surface. In principle a direct experimental test of this proposal is possible.