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Pure hydride of the α-UH type without any β-UH admixture was prepared by high-pressure hydrogenation of U stabilized by Zr. Such material, characterized by a general formula (UH) Zr , is stable in air at ambient and elevated temperatures. H release is observed between 400-450 °C similar to β-UH. Its stability allowed to measure magnetic properties, specific heat, and electrical resistivity in a wide temperature range. Despite rather different crystal structure and inter-U spacing, the electronic properties are almost identical to β-UH. Its ferromagnetic ground state with Curie temperature ≈ 180 K (weakly and non-monotonously dependent on Zr concentration) and U moments of 1.0 μ indicate why mixtures of α- and β-UH exhibited only one transition. Magnetic ordering leads to a large spontaneous magnetostriction = 3.210, which can be explained by the increase of the spin moment between the paramagnetic (Disordered Local Moment) and the ferromagnetic state. The role of orbital moments in magnetism is indicated by fully relativistic electronic structure calculations.

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