CO Chemisorption on Ni(110): Effect on Surface Magnetism

Abstract

The effect of CO chemisorption on the surface magnetism and unfilled electronic structure of Ni(llO) is investigated by spin-polarized inverse-photoemission spectroscopy. A saturation in the reduction of the unfilled minority-spin d density of states is observed near 0.5-monolayer CO coverage and attributed to a reduction in the Ni-atom magnetic moments. Transitions into the CO w* band are also observed with an intensity that increases nearly linearly with coverage. No transference of spin polarization from the Ni substrate to the CO IT* is found. PACS numbers: 79.60.Gs, 75.50.Cc Because there is strong coupling between the valence electrons in metal atoms of a solid, it follows that adsorption of a molecule on a metal surface should have an effect not only on the electronic structure of substrate atoms directly involved in the chemisorption bond, but on the subsurface and nearestneighbor atoms as well. Various theoretical studies of chemisorption support this view, 1 "" 3 and the wellknown sensitivity of surface states to small amounts of contamination provide experimental evidence for this "through-metal effect" on the surface electronic structure. In ferromagnetic substrates, surface magnetism also exhibits a high sensitivity to contamination. 4 " 8 Magnetism, when viewed as a macroscopic phenomenon, has its basis in the long-range ordering of the individual magnetic moments of the atoms, whereas the basis for the magnitude of the moments is derived from details of the ferromagnet's valence electronic structure. Early studies 4 ** 6 on the effect of chemisorption on magnetism were not able to distinguish whether the chemisorption-induced reduction in surface magnetism is due to a disruption of the longrange ordering of the magnetic moments or an actual reduction in the moments themselves. Only recently have there emerged experiments of sufficient detail to show the correlated effect that chemisorption has on the substrate magnetic and electronic structure. 7,8 In this Letter, we present the results of measurements on the effect of chemisorption of CO on the surface magnetic and electronic structure of Ni(110) using spin-polarized inverse-photoemission spectroscopy (SPIPES). These measurements indicate that the decrease in surface magnetism that is induced by CO chemisorption is a result of a reduction in the magnetic moments (or net spin) of the atoms rather than a reduction of the exchange coupling leading to a disordering of otherwise unchanged moments.

Ab initiostudy of CO adsorption on Ni(110): Effects on surface magnetism at low coverage

“…The behavior of the magnetic moment of the surface layer as a function of the CO coverage is also in qualitative agreement with spin-polarized inversephotoemission measurements. 2 Concerning the clean surface, the results of Table I are in good agreement with those of Mittendorfer et al 9 calculated in the Perdew-Wang approximation. All values obtained with pseudopotential techniques are larger than those obtained with the all-electron method.…”

“…1 The adsorption of CO molecules on magnetic surfaces is known to reduce the enhanced magnetic moment of the surface layer as a result of a complex electronic charge transfer between adsorbate and substrate. [2][3][4][5][6][7][8] By means of spin-polarized inverse photoemission experiments, it has been shown, for instance, that Ni͑110͒ surfaces subject to increasing CO exposure exhibit a reduction of the unfilled minority-spin d density of states with a saturation near 0.5-ML CO coverage. 2 The interpretation of this result was that CO adsorption locally reduces Ni-atom magnetic moments by partially filling the corresponding minority-spin states.…”

Surface magnetic states of Ni nanochains modified by using different organic surfactants

“…The chemisorption of CO on the metallic Ni surface leads to the quenching of Ni magnetic moments because electrons 4 of the carbonyl ligation drive the Ni 4s electrons to fill up the 3d shell by repulsive interaction. The Ni atoms in the surface layer, therefore, become nonmagnetic (NM), leaving the magnetism of the inner core unaffected [12,13]. In many cases, surface magnetic effects are usually featured with a surface spin glass (SG) state and an appreciable reduction of saturation magnetization.…”

STM-induced desorption of hydrogen from Co nanoislands

“…When the magnetic domain structure depends strongly on surface anisotropy, it is also possible to use surface chemisorption to rotate the magnetic easy axis [1][2][3] or to obtain dead magnetic layers. [4][5][6][7] These modifications are often reversible since thermal annealing allows for total desorption of the adsorbate. However, it is important to realize that desorption occurs for all particles affecting the entire system.…”