Spin dependence in He(23S) metastable-atom deexcitation at magnetized Fe(110) and O/Fe(110) surfaces

Spin-labeling techniques, specifically the use of electron-spin-polarized He(2 exp 3 S) metastable atoms coupled with analysis of the number and spin of the ejected electrons, are used to investigate the dynamics of metastable-atom--surface interactions and the properties of (magnetized) Fe(110) and O /Fe(110) surfaces. The data show that the dominant He(2 exp 3 S) metastable-atom deexcitation mechanism at such surfaces is resonance ionization followed by Auger neutralization, and that the ejected-electron polarization reflects the Fe conduction-band polarization. The present results, when interpreted using the theory of Penn and Apell, also indicate that the magnetization in the vacuum above a clean Fe(110) surface at distances ( approx 3-5A) where Auger neutralization occurs is negative but changes sign upon exposure to oxygen. Several possible explanations for this sign reversal are discussed. The measurements establish spin-polarized metastable-atom deexcitation spectroscopy as an extraoridinarily sensitive probe of the surface magnetic environment.