First direct evidence for a magnetic phase transition in the heavy-electron system UCd11

Muon-spin-rotation and relaxation measurements performed on polycrystalline UCd₁₁ give first direct evidence for an antiferromagnetic phase transition at 5 K. As far as probed by the positive muon the behaviour close to the phase transition is clearly contrasted to that in other magnetic heavy-electron materials investigated by μ⁺SR, e.g. U₂Zn₁₇ and UCu₅, because in UCd₁₁ longitudinal field measurements reveal dynamic relaxation effects which are attributed to the critical slowing down of the uranium 5f-moments. No signal could be observed in the ordered regime because of a large dipolar field spread.