Magnetization study of UFe 2

Abstract

Bulk magnetization measurements have been performed between 4 and 400 K on oriented samples cut from a single crystal of UFe 2 (cubic C15-type Laves phase) used in an earlier neutron-diffraction study. The easy axis of magnetization was determined to be 〈111〉 in all cases, but the samples differed from each other in bulk magnetic properties (particularly Curie temperatures, which varied from 147 to 162 K). These variations apparently reflect small differences in stoichiometry. The upper temperature limit of the measurements was determined by the increasing presence of an “impurity” magnetization presumably arising from the precipitation of small amounts (≈0.01%) of free iron. This result implies that samples of UFe 2 quenched from elevated temperatures are not stable, under equilibrium conditions, near room temperature. Subsequent measurements on polycrystalline samples deliberately prepared with excess uranium (UFe 2− x ) showed that the C15-type structure persists to at least UFe 1.7 and that the magnetic properties vary regularly with changes in stoichiometry. The bulk magnetic moment (1.09 μ B/mol) determined from a 〈111〉 oriented single crystal is significantly larger than the total moment obtained in the neutron-diffraction study on the same sample.