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 and NMR experiments support the hypothesis that the transition at T-N is to a single-domain 4-q magnetic structure which transforms into a multi-domain 1-q structure below T-2. In studies of the magnetisation, resistivity and magnetoresistivity of UCu5-xAgx compounds, we have found that the nature of the low-temperature phase transition is significantly changed as result of doping with Ag. In UCu4Ag the resistivity decreases below T-2, whilst in UCu5 a large increase takes place. The field dependence of the phases in UCu4Ag is reported.