Ferromagnetism in UMn ₂Al ₂₀ studied with polarized neutron diffraction and bulk magnetic measurements

Polarized neutron and bulk magnetic measurements were performed on a high-quality single crystal of UMn ₂Al ₂₀. Magnetization data indicated a ferromagnetic ordering that sets in below T _C=17.5K. Near-zero-field measurements of the magnetization confirmed the spontaneous nature of the magnetic order. The magnetization density maps, rendered using the maximum-entropy method, clearly showed that the magnetic moments are present on the Mn sites only, which was not hitherto suggested. The spontaneous moment value derived from the polarized neutron flipping ratios agrees with that obtained from the bulk magnetization data, and its magnitude hints at the itinerant character of the magnetic state.