THEORY OF TEMPERATURE-DEPENDENT PHOTOEMISSION IN 3D-BAND FERROMAGNETS - APPLICATION TO NI(110) AND NI(111)

The effects of electron correlations and phonons on the temperature dependence of ultraviolet photoemission and bremsstrahlung isochromat spectra of ferromagnetic Ni are investigated. The spin- and temperature-dependent photocurrent is calculated in the framework of a generalized one-step model of photoemission. Phonons are taken into account via temperature-dependent phase shifts. The hole state of photoemission is described by an energy-, spin-, and temperature-dependent self-energy, which rests on a combination of density-functional theory and a Hubbard-type multiband model. The comparison of calculated spin-polarized and temperature-dependent spectra for Ni(110) and Ni(111) with experimental data shows excellent agreement, in particular for the Ni(110) surface. No indication of a stationary exchange splitting independent of temperature could be found. Instead the merging of the majority and minority spin states upon approaching the Curie temperature T(C) was identified unambiguously in essentially all relevant cases.