Nuclear Magnetic Resonance in Uranium Hydride and Deuteride

β-uranium-hydride and β-uranium-deuteride are ferromagnetic with Curie temperatures of 182 and 178^∘{}K, respectively. Nuclear-magnetic-resonance studies of the proton in β-UH₃, and of the deuteron in β-UD₃, were made in the paramagnetic state of these compounds. The measured hydrogen Knight shifts (K) in β-UH₃ and β-UD₃ are given by K=(0.40±0.03)χM, where χM is the molar susceptibility. The second moments are determined as M₂=(24±2)+(45±3)×10^-4h² Oe² in β-UH₃, and M₂=(56.4±1.5)+(48.5±3)×10^-4h² Oe² in β-UD₃, where h=H₀(T-θ), θ being the appropriate paramagnetic Curie temperature. Analysis of the linewidth, line shape, and second moment showed that there are three line-broadening mechanisms (four in the deuteride): internuclear dipolar broadening, the (classical) dipolar field of the $5f$ electrons on the uranium ions, and an effect due to the use of powder samples (in the deuteride, a quadrupolar interaction is also present, with |e²qQh|=14.5±0.5 kHz). The line shapes, due to the simultaneous presence of several broadening mechanisms, are discussed in some detail. The $5f$ electrons are shown to be localized and do not form a band. The ferromagnetic interaction was analyzed using a simple Ruderman-Kittel-Kasuya-Yosida model, from which it is deduced that the coupling constant Γ~20 eV ³, m*mₑ~3, and the concentration of conduction electrons is about 2.5 per uranium ion. The Knight shift and quadrupole shielding were calculated, assuming the presence of a high-density interacting electron gas. At temperatures above 370^∘{}K, line narrowing was observed, from which the activation energy for hydrogen diffusion was obtained as E=8.4±0.9 kcal/mole for the hydride and 8.9±{}0.9 kcal/mole for the deuteride. It was concluded, on the basis of the pre-exponential term τ₀ of the correlation time τc, that diffusion takes place by a vacancy mechanism, and that the higher values of τ₀ and τc for the deuterium are mainly due to a difference in the relaxation mechanism. The valency of the uranium ions present has not been definitely established; they are either U³⁺ or U⁴⁺, probably the latter.