| AVS 62nd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+AS+MI-WeM |
| Session: | Magnetism, Complexity and Superconductivity in the Actinides and Rare Earths |
| Presenter: | Ladislav Havela, Charles University, Czech Republic |
| Authors: | L. Havela, Charles University, Czech Republic M. Paukov, Charles University, Czech Republic I. Tkach, Charles University, Czech Republic M. Cieslar, Charles University, Czech Republic Z. Matej, Charles University, Czech Republic D. Kriegner, Charles University, Czech Republic D. Drozdenko, Charles University, Czech Republic I. Turek, Charles University, Czech Republic M. Divis, Charles University, Czech Republic N.-T.H. Kim-Ngan, Pegagogical University, Poland |
| Correspondent: | Click to Email |
Several routes of preparation of alloyed U trihydrides, UH3, were discovered. Starting from the U6T compounds, hydrogenation leads to T atoms embedded in the β-UH3 structure, with transition-metal atoms T occupying one of the U sites. We have been hydrogenating γ-U alloys, using various transition metals helping (together with ultrafast cooling) to retain the bcc U structure down to low temperatures. As such alloys are much more resistant to hydrogen attack, high pressures of H2 gas had to be applied. The H absorption corresponds to approx. 3H/atoms per 1 U atom. In none of the cases the alloying metals segregate and two different structures were obtained. The hydrides (UH3)1-xZrx form the α-UH3 structure, i.e. the bcc structure expands and fills by H. Hence basic electronic properties of α-UH3 could be established. Starting from U1-xMox, we obtained (UH3)1-xMox, which tends to be β-UH3 like, but has the grain size is 1 nm only, i.e. practically amorphous. This amorphous phase also easily accepts additional dopants, as Zr, Fe, Ti, V...however magnetic properties remain only weakly affected. It is quite remarkable that all such materials are ferromagnets with the Curie temperature in the range 160-205 K, even if the active U sublattice is diluted by more than 30% of other metals. In this respect the hydrides are different than conventional band ferromagnets, sensitive to inter-atomic spacings and alloying. Albeit all are metallic, the U-H interaction, which can have a partly ionic character, plays clearly important role. Electronic structure calculations (performed for the α-UH3 structure and in ferromagnetic or Disordered Local Moment state, with possible random Zr occupancy) suggest a transfer of U-6d and 7s electrons into H-1s states, reducing the hybridization of 5f and non-f states, supporting thus magnetism even if the U-U spacing is below the Hill limit [1].
[1] I. Tkach et al. Phys.Rev. B 91, 115116 (2015).