Spin and orbital magnetism in UH₂ thin films studied by X-ray magnetic circular dichroism

Uranium dihydride UH₂ is a metastable phase unknown in bulk form but accessible through thin-film synthesis. We prepared UH₂ films by reactive dc sputtering on CaF₂ (001) or Si(001) substrates, the latter equipped with a Mo buffer layer to suppress a U-Si interdiffusion. On CaF₂, UH₂ adopts the fluorite-type structure with a near-[1 1 1] out-of-plane texture, four rotational domains, and a lattice parameter a = 539 ± 3 pm without measurable strain, whereas the Mo-buffered film is polycrystalline. X-ray photoelectron spectroscopy confirmed complete hydrogenation and minimal oxidation. Magnetization and XMCD measurements show ferromagnetic ordering with Curie temperatures of 120–130 K and a uranium 5f moment of ≈ 0.9 μ_B/U, dominated by the orbital contribution (μ_L ≈ 1.4 μ_B, μ_S ≈ −0.5 μ_B), in a good agreement with GGA + U computations, which otherwise overestimate absolute values of the spin and orbital components. The slightly reduced moment in thinner CaF₂-supported films is attributed to surface U(IV) species. These results demonstrate that thin-film synthesis enables stabilization of UH₂ and direct probing of 5f magnetism, opening pathways toward higher uranium hydrides and interface-engineered actinide systems.