The d-band holes which give rise to ferromagnetism in Ni can be directly observed by spin-polarized inverse photoelectron spectroscopy (SPIPES). Only incident electrons polarized in the minority spin direction can fall into unfilled minority spin states and radiate a detected photon. On dissociative chemisorption of O2 we observe a reduction in the number of minority spin d holes. It is this change in electronic structure which gives rise to a decrease in magnetization. A background of minority and majority spin states remains essentially unchanged. Further exposure to oxygen causes formation of NiO; the surface magnetization goes to zero, and a completely different SPIPES spectrum is observed. The relative importance of d electrons and s, p electrons in chemisorptive bonding on Ni has been much discussed. These data suggest that the d states interact strongly with the oxygen and that this interaction has a profound influence on the surface magnetism.
Citation: Journal of Applied Physics
Pub Type: Journals