Abstract
Pure hydride of the alpha-UH3 type without any beta-UH3 admixture was prepared by high-pressure hydrogenation of bcc U stabilized by Zr. Such material, characterized by a general formula (UH3)(1-x)Zr-x, is stable in air at ambient and elevated temperatures.
Hrelease is observed in the range of 400-600 degrees C similar to beta-UH3. Its stability allowed us to measure the magnetic properties, specific heat, and electrical resistivity in a wide temperature range.
Despite the rather different crystal structure and inter-U spacing, the electronic properties are almost identical to beta-UH3. Its ferromagnetic ground state with Curie temperature T-C approximate to 180K (weakly and nonmonotonously dependent on Zr concentration) and U moments of 1.0 mu B indicate why mixtures of alpha- and beta-UH3 exhibited only one transition.
Magnetic ordering leads to a large spontaneous magnetostriction omega(s) = 3.2 x 10(-3), which can be explained by the increase of the spin moment between the paramagnetic (disordered local moment) and the ferromagnetic states. The role of orbital moments in magnetism is indicated by fully relativistic electronic structure calculations.