TEMPERATURE-DEPENDENT ELECTRONIC-STRUCTURE OF NICKEL METAL

An extended set of temperature-dependent ARUPS data from Ni(111) is pr esented. The ferromagnetic and the paramagnetic state as well as the p hase transition are examined in great detail. Rather new and unconvent ional modes of data acquisition in ARUPS are applied with high angular and energy resolution, exhibiting great power near the Fermi energy E -F. Even up to 5 k(B)T above E-F energy bands are readily observed. Th e understanding of these ARUPS data is strongly enhanced by spin-polar ized band structure calculations. Exchange-split bands of both, sp- an d d-character, are resolved in angular scans and in photoemission Ferm i-surface maps. From two-dimensional data sets in energy and angle the dispersion and the exchange splitting are obtained with high precisio n. All the observed sp- and d-bands clearly exhibit a Stoner-like coll apsing-band behavior. The exchange splitting Delta E-ex vanishes above T-C in all cases, and Delta E-ex closely follows the temperature depe ndence of the macroscopic magnetization. The apparent deviations from the Stoner-like band behavior stated in P. Aebi et al., Phys. Rev. Let t. 76, 1150 (1996) are explained. Furthermore we detect anomalously hi gh intensity from a minority d-band close to an sp-band. This strongly suggests that sp-d-fluctuations at the Fermi level are a driving forc e for the magnetic phase transition of nickel. [S0163-1829(98)01527-6] .