Theory of spin-polarized metastable-atom-deexcitation spectroscopy: Ni-He

Metastable spin-polarized ${\mathrm{He}}^{\mathrm{*}}$ atoms incident on a Ni surface undergo deexcitation in a process which yields electrons from the Ni. The number produced is observed to depend on the relative spin of the Ni and the ${\mathrm{He}}^{\mathrm{*}}$ atoms. The normalized difference in the ejected-electron intensity produced by ${\mathrm{He}}^{\mathrm{*}}$ atoms with opposite spin polarizations increases dramatically with increasing kinetic energy of the electrons. A theory of this asymmetry is presented. It is found that the experimental results can be reproduced only by the use of a realistic potential for the Ni electrons in the vacuum region. With such a potential it is found that ${\mathrm{He}}^{+}$ ions which result from the ${\mathrm{He}}^{\mathrm{*}}$-surface interaction are neutralized at ∼4.5 Å from the Ni surface, a much larger distance than given by previous estimates. The experiment is shown to reflect the polarization of Ni electrons at the He ion, and it is estimated that the Ni magnetization at the Fermi energy and far from the Ni surface is ≃-20%.