Photoemission with high angular and energy resolution: Temperature dependent exchange splitting in nickel

Ultraviolet photoemission spectroscopy data from a Ni(110) crystal taken with high angular and energy resolution at room temperature (RT) and near the ferromagnetic Curie temperature are presented. For a polar scan in the (001) plane we recorded energy spectra within 1.5 eV from the Fermi energy (E_F) in 1° steps. Distinct bands crossing E_F can be well separated and, by comparing the RT data with a recent band structure calculation [H. Eckardt, L. Fritsche, <i>J. Phys. F</i><b>17</b>, 925 (1987)], the bands can be assigned to a minority d-band and two exchange split <i>sp</i>-bands. While their exchange splitting can hardly be extracted from the energy spectra, the peaks are well separated in <b>k</b>-space, i.e., in polar angle. We determine ΔE_ex = 204±8 meV for the <i>sp</i>-band in the examined <b>k</b>-region and find that the angular line width of the majority <i>sp</i>-band is significantly smaller than that of the minority <i>sp</i>-band. Upon approaching T_C the exchange splitting of the <i>sp</i>-band vanishes and the <i>d</i>-band becomes very broad.