Looking at magnetism with photoemission

Abstract

With photoelectron spectroscopy one can directly observe the electrons in incomplete shells and study their interaction with the core electrons. The greatest relevance to magnetism lies in the ability to map the dispersion of the electronic bands, resolving even the spin-splitting in ferromagnetic transition metals. Additional information is obtained by measuring the spinpolarization of the photoelectrons. In rare earth systems the occupancy of the 4f shell is unambiguously determined by the characteristic final-state multiplet structure. This feature has found application in the study of mixed-valence compounds. Core level spectra yield information about the electronic configuration of the atom rather than about the collective aspects of magnetism. In insulators the core s-electron spectra of paramagnetic ions exhibit a splitting due to the coupling of the spin of the core hole to that of the incomplete outer shell. The interpretation of such data, especially from the deeper core levels, is significantly complicated by many-electron processes caused by the creation of the core hole. They may involve not only the familiar conduction electron screening, but also charge transfer to the photoexcited atom in the final state.