Variations of magnetic properties of UGa2 under pressure

Abstract

Electrical resistivity \rho(T) of the 5f ferromagnet UGa2 was investigated for single-crystal samples as a function of pressure and magnetic field. The Curie temperature monotonously increases from T$_{C}$ = 124 K under quasi-hydrostatic pressure up to 154 K at p = 14.2 GPa, after which it turns down steeply and reaches T$_{C}$ = 147 K at p = 15.2 GPa. At 20 GPa the compound is already non-magnetic. This dramatic variation is compatible with exchange interactions mediated by the 5f hybridization with the non-f states. The external pressure first enhances the exchange coupling of the 5f moments, but eventually suppresses the order by washing out the 5f moments. Such a two-band model is adequate for the weakly delocalized 5f states. The spin-disorder resistivity, which produces very high \rho-values (300 \mu\Omega.cm) is gradually suppressed by the pressure. In the paramagnetic state, this leads to a crossover from initial negative to positive d\rho/dT.