Ladislav Havela1 Mykhaylo Paukov1 Milan Dopita1 Daria Drozdenko1 Ilja Turek2 Martin Divis1 Thomas Gouder2 Frank Huber2 Alice Seibert2

1, Charles University, Prague 2, , Czechia
2, European Commission Joint Research Centre, Karlsruhe, , Germany

Properties of Uranium hydride, the oldest known 5f ferromagnet, haven't been yet really well established, despite decades of research. The reason is primarily the form of the material, which is normally obtained as a fine pyrophoric powder. Hence it is rather difficult to obtain a reliable information on basic features of electronic structure by means of electron spectroscopies. Another principially possible route is in-situ synthesis of the hydride films by means of reactive sputtering in H2 containing atmosphere, although interaction of hydrogen with UHV systems may lead to a disappointing oxidation. This route proved feasible, yielding basic valence-band and 4f core-level spectra for UH3 [1]. Here we present results of an extended spectroscopic study of U, U-Mo, and (U,Mo)H3 films studied by XPS (using monochromatized Al-Kα radiation), UPS (using He I and He II UV) and by Bremsstrahlung Isochromat Spectroscopy (BIS), the last providing information on empty electronic states above the Fermi level. The study si complemented by ex-situ XRD study, proving that the sputter deposition leads to β-UH3 type of hydride, which is, however, highly textured and exhibits large compressive residual strain. The results are confronted with fully relativistic ab-initio calculations, providing an overall agreement of energies of large scale spectral features. The situation around the Fermi level is, however, showing some discrepancy between the theory and experiment, which may indicate many body effects. Those would be rather unexpected in a band 5f-system, assumed at least as a good starting point for description of uranium compound with short U-U spacing of 330 pm. The data will be discussed from the point of view of possible charge transfer between the U-6d and 7s states and the H-1s states, its impact on the U-5f states, which can be one of reasons of the relatively very high Curie temperature of 165 K. The study also revealed interesting structure variations of the hydrides depending on the substrate material and temperature.

The work at the Charles University was supported by the Czech Science Foundation under the grant No. 15-01100S.

[1] T. Gouder et al., Phys.Rev. B 70, 235108 (2004).