- Mgr. Mikhaylo Paukov: Magnetism hydrides of gamma-Uranium alloys
- 4. 12. 2013, 14:00
- Seminar room KFM, first floor Ke Karlovu 5
- more information
Abstract:
The bcc form of Uranium metal (gamma-U) is stable at elevated temperatures. The only possibility to retain this phase to low temperatures is to combine doping (by Mo, Zr, Ti, Nb, Re, Ru, Pd, or Pt) with quenching. It opens the possibility to study the ground state properties in this form of U. The Pauli paramagnetism of such systems opens a possibility for conventional superconductivity. Using the splat-cooling technique allowed us to reduce dopants concentration in the alloys and to get the pure bcc alloy retained.
The common alpha-U phase is known to react readily with H at low pressures already, producing a fine pyrophoric powder of beta-UH3, which is ferromagnetic with the Curie temperature around 170 K. As the interaction of hydrogen is one of important factors for applications of U in technology, a question appeared what would be the reaction of doped bcc U with H. Experiments revealed that the Mo stabilized gamma-U absorbs H only at elevated pressure. The product is surprisingly not powder. We obtained brittle but compact pieces of hydrides denoted as UH3Mox with practically amorphous crystal structure, most likely related to UH3. Varying the Mo concentration, we found that the Curie temperatures increase up to 200 K. The magnetic moment per U atom increases as well.
For comparison, we undertook the same type of study with bcc U doped by Zr. In this case the amorphization does not happen. The crystal structure obtained corresponds to that of alpha-UH3, the rather unstable form of U hydride, which was never successfully prepared in a pure form, and the magnetic properties of which were a subject of dispute. This structure is in fact a bcc U lattice expanded and filled with H. We proved that it is ferromagnetic with spontaneous moment and ordering temperatures very close to beta-UH3. The research opened questions to which extent we actually understand electronic properties of UH3, one of the first U-based ferromagnets, and why in some cases amorphization does not lead to suppression of the 5f moments