| AVS 64th International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Monday Sessions |
| Session AC+AS+SA+SU-MoA |
| Session: | Chemistry and Physics of the Actinides and Rare Earths |
| Presenter: | Ladislav Havela, Charles University, Prague, Czech Republic |
| Authors: | L. Havela, Charles University, Prague, Czech Republic M. Paukov, Charles University, Prague, Czech Republic M. Dopita, Charles University, Prague, Czech Republic L. Horak, Charles University, Prague, Czech Republic M. Divis, Charles University, Prague, Czech Republic I. Turek, Charles University, Prague, Czech Republic T. Gouder, European Commission, Joint Research Centre, Karlsruhe, Germany A. Seibert, European Commission, Joint Research Centre, Karlsruhe, Germany F. Huber, European Commission, Joint Research Centre, Karlsruhe, Germany D. Legut, VSB - Technical University of Ostrava |
| Correspondent: | Click to Email |
U hydride was the first material indicating that 5f states can yield ferromagnetism analogous to 3d metals. However, the electronic structure of UH3 is not yet well understood, and it is not clear to which extent it can be described by conventional band structure calculations. We have been studying structure and electronic properties of UH3 and (UH3)1-xMox films synthesized by reactive sputtering. Primary diagnostics was performed by in-situ XPS. The U-4f core level spectra exhibit a development as a function of partial pressure of H2 in Ar (pAr = 8*10-3 mbar). Their intensity gradually decreases, they shift by 0.2 eV towards higher binding energies (BE) and an extended (9 eV wide) satellite structure develops on the high BE side of both 4f peaks. This tendency saturates at 5% H2 concentration, and we assume that this pressure is sufficient to form UH3. XRD and X-ray reflectivity proved indeed the β-UH3 structure of deposited films, which were polycrystalline, but highly textured. Ferromagnetism of the UH3 films has the correct Curie temperature TC ≈ 165 K. Magnetic coercivity of the films is enormous, the width of hysteresis loop exceeds 10 T at low temperatures. Details of the valence band observed in UPS reveal a transformation of the triangular emission of the U metal into a sharp feature at the Fermi level accompanied by a broad shoulder around 0.5 eV for the hydride. A distinct development was noticed also for the U-6p states, which become narrower and shift by 1.2 eV to higher BE in the hydride, which can be interpreted as an impact charge transfer from U towards H. Besides photoelectron spectroscopy, the variations of electronic states were monitored also by BIS spectra collected for the 1486.6 eV photon energy. The spectroscopy results are confronted with different types of in-initio calculations.
As U-Mo alloys tend to form nanocrystalline β-UH3 based hydrides, we were curious about reactive sputter deposition of the U-Mo alloys. We found that the tendency to form hydrides is fast suppressed by Mo for room temperature sputtering (γ-U alloy without H is the product), but cooling the substrate to 77 K helps to maintain the hydride phase even for even higher Mo concentrations.
This work was supported by the Czech Science Foundation under the grant No. 15-01100S.