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Pressure variations of the Curie temperature of the 5f ferromagnet β-UH3 were studied using the Mo-alloyed hydride (UH3)0.82Mo0.18, which is stable in air and has very similar TC and magnetization per U atom. By means of ac magnetic susceptibility a linear decrease of TC was observed for pressures up to 3.2 GPa. The coefficient dTC/dp = −2.05 K/GPa gives dlnTC/dp = 1/T*dTC/dp ≈ −0.011 GPa−1. This value is smaller than expected for a 5f-band ferromagnet with relatively short U-U distances and suggests that UH3 may be more localized than expected. Among AnX compounds, similar dependence was found e.g. for US. Revisiting existing data on lattice elasticity for β-UH3, bulk modulus B ≈ 100 GPa can be assumed, leading to dlnTC/dlnV = 1.1. Experimental data are confronted with results of GGA + U electronic structure calculations. Plausible values of direct Coulomb U and Hund’s exchange J are deduced. The lattice compression was found to reduce predominantly the orbital moments.

Uranium hydride films with the β-UH3 structure were successfully synthesized using reactive sputter deposition. Their composition can be modified, if cooling the substrate to 177 K, by incorporating Mo as alloying element, in analogy to bulk nanocrystalline (UH3)-Mo hydrides. The films were in detail studied by in situ XPS (4f, 5d, 6p, valence band), valence-band UPS, and BIS, revealing variations of electronic structure with respect to U metal, confronted with ab initio calculations. We could identify certain ionicity in the U-H bonding projected in a large shift of the 6p peaks to higher binding energies. The U-6d states partly shift above the Fermi level and partly hybridize with the H-1s states, which weakens the 5f-6d hybridization. Although large scale features of the band structure are consistently explained and 5f states remain at the Fermi level EF, spectral features close to EF are not well reproduced by DFT or DFT+U calculations. This situation suggests prominence of electron-electron correlations affecting spectral function in the conditions of intermediate 5f localization.