Hard x-ray photoemission spectroscopy of GdNi and HoNi

We study the electronic structure of GdNi and HoNi, which are magnetic materials with a Curie temperature T-c = 69 and T-c = 36 K, respectively. These materials are useful for magnetic refrigerator applications at low temperature as they exhibit a large magnetocaloric effect near T-c. We have used hard x-ray photoemission spectroscopy (HAXPES) to investigate the core-level and valence-band electronic states of GdNi and HoNi. HAXPES measurements of the Gd and Ho 3d, 4d, 4p, 5p, and 4s core-level spectra have been compared with atomic multiplet calculations of Gd3+ and Ho3+ ionic configurations. The good match between the experimental and calculated spectra clarify the important role of spin-orbit coupling, as well as Coulomb and exchange interactions in the intermediate-coupling scheme. The core-level spectra also show plasmons in addition to the atomic multiplets. The Gd and Ho 4s spectra show clear evidence of exchange splitting. The Ni 2p and 3s spectra of GdNi and HoNi show a correlation satellite at a binding energy of 7 eV above their main peaks. The Ni 2p and Ni 3s spectra could be reproduced using charge transfer multiplet calculations. Valence-band HAXPES of GdNi and HoNi shows that the Gd 4f and Ho 4f features are also consistent with atomic multiplets and occur at high binding energies away from the Fermi level. The Ni 3d density of states are spread from the Fermi level to about 3 eV binding energy. The results indicate a partially filled Ni 3d band and show that the charge transfer model is not valid for describing the electronic structure of GdNi and HoNi.