LOW-TEMPERATURE MAGNETIC PHASE-TRANSITIONS IN UCU5-XAGX COMPOUNDS

The heavy fermion compound UCu5 exhibits magnetic phase transitions at T-N approximate to 16 K and T-2 approximate to 1.2 K. Magnetisation a nd NMR experiments support the hypothesis that the transition at T-N i s to a single-domain 4-q magnetic structure which transforms into a mu lti-domain 1-q structure below T-2. In studies of the magnetisation, r esistivity and magnetoresistivity of UCu5-xAgx compounds, we have foun d that the nature of the low-temperature phase transition is significa ntly changed as result of doping with Ag. In UCu4Ag the resistivity de creases below T-2, whilst in UCu5 a large increase takes place. The fi eld dependence of the phases in UCu4Ag is reported.