Pressure variations of the 5f magnetism in UH3

•Curie temperature of beta-UH3 decreases with pressure to 3.2 GPa.•The linear decrease approx. −2 K/GPa is linear and weaker than assumed before.•The decrease indicates intermediate 5f delocalization.•Basic features are captured by GGA + U method. 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.