Chemically selective gas-induced spin polarization changes in ultrathin fcc Co films

Abstract

The influence of submonolayer quantities of O and N adsorbed on ultrathin Co∕Cu(001) films as a function of Co thickness has been studied using spin polarized secondary electron spectroscopy. The gaseous adsorbate was prepared by depositing Co on (2×22)R45°-O and c(2×2)-N reconstructed Cu(001) utilizing surfactant effects to reproducibly control quantity. Adsorbed quantities were monitored by Auger electron spectroscopy and surface reconstructions by low energy electron diffraction. The secondary electron spin polarization increases with the Co film thickness, following an exponential law, and the chemical interaction between the adsorbate and the Co reduces polarization to (98±2)% in the case of O and (84±3)% in the case of N compared to the uncovered substrate. For both, the onset of ferromagnetism is suppressed by approximately 1 ML. The effects on polarization and the onset of ferromagnetism are attributed to the partial cancellation of the magnetic moment in the Co layer adjacent to the adsorbate. The estimated reduction in moment is comparable to the results of theoretical predictions.

Magnetism in ultrathin film structures

“…For thicknesses above 5 nm the uniaxial anisotropy vanishes and the [1 1 1] direction becomes the magnetic easy axis, as in bulk fcc Co. The effect of O and N adsorbates on the Cu(0 0 1) substrate is also found to affect the magnetic properties of Co films up to 12 ML in thickness [1254].…”

Chemically selective modification of spin polarization in ultrathin ferromagnetic films: Microscopic theory and macroscopic experiment

“…AES measurements confirm that the adsorbed quantity of gas is constant during change of substrate from Cu to Co, and corresponds to 0.5 ML. 25,28 Secondary electrons are excited by primary electrons of 1 keV ͑Ref. 25͒ and the measured polarization arises from emitted electrons with secondary energies from zero to the primary excitation energy.…”