Quenching of ferromagnetism in β-UB2C and UNiSi2 at high pressure

Abstract

β-UB2C exhibits itinerant ferromagnetism below Tc = 75 K; whereas, UNiSi2 exhibits ferromagnetism of localized uranium moments below Tc = 95 K and Kondo lattice behaviour at higher temperatures. We have found that ferromagnetism in both compounds is quenched at high pressure. In β-UB2C the Curie temperature continuously approaches zero at 2.95 GPa, where resistivity and specific heat reveal the behaviour similar to that observed in Ce-based antiferromagnets near quantum critical points. In UNiSi2 the Curie temperature decreases gradually to 25 K at 5.34 GPa. Above this pressure hysteretic phenomena appear in the temperature dependences of resistivity between 5 and 17 K, signalling a change in the magnetic order. No signature of magnetism was found above 5.5 GPa down to 1.15 K. Kondo lattice behaviour of resistivity with the enhanced residual resistivity is observed in UNiSi2 above 5.5 GPa.