Spin and Orbital Magnetism in UH2 Thin Films Studied by X-ray Magnetic Circular Dichroism

TL;DR

This study synthesizes and characterizes UH2 thin films, revealing ferromagnetic 5f electron magnetism with orbital dominance, and demonstrates the potential of thin-film methods to explore uranium hydrides and actinide interfaces.

Contribution

It provides the first detailed magnetic characterization of UH2 thin films, showing ferromagnetism and orbital dominance, and compares experimental results with GGA+U calculations.

Findings

UH2 thin films are ferromagnetic with T_C of 120-130 K

Uranium 5f moments are dominated by orbital contributions

Thin-film synthesis stabilizes UH2 and enables magnetic probing

Abstract

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 {\mu}B/U, dominated by the orbital contribution ({\mu}L ~ 1.4 {\mu}B, {\mu}S ~ -0.5 {\mu}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.