Calculated photoemission and many body effects in 3d-ferromagnets

Abstract

The influence of electron correlations on the temperature dependence of ultraviolet photoemission and bremsstrahlung isochromat spectra of ferromagnetic Ni is investigated. The calculations are performed within the framework of the one-step model of photoemission using an expression for the energy-, spin- and temperature-dependent self-energy of the hole state, which rests on a combination of the results of density functional theory and those of a generalized Hubbard model. The model contains only two parameters, the Hubbard U and the interband exchange J. It is approximately solved by use of a selfconsistent moment method and has so far resulted in an excellent description of macroscopic magnetic properties, like the magnetic moment at T = 0, the Curie temperature, a Brillouin-like magnetization curve and a strict Curie-Weiss behaviour of the paramagnetic susceptibility. In this contribution we demonstrate the virtues of this theory for quasiparticle properties in Ni by calculating spin-polarized and temperature-dependent photoemission spectra and comparing with experimental results available in literature. The theoretical photoemission results for the occupied d-bands are shown to be in excellent agreement with the experiment. Since the ferromagnetism and the many body effects in Ni are mainly caused by the uppermost d-band, which is only partly occupied, we also calculate the spin-polarized inverse photoemission spectra for this subband and compare with the most recent experimental results obtained in bresstrahlung isochromat spectroscopy.