Pressure-induced antiferromagnetism in UPt

UPt orders ferromagnetically at ambient pressure at 28 K. Upon increasing pressure, an additional magnetic phase transition appears around 17 K. While the upper transition behaves with field as a typical paramagnetic-ferromagnetic transition, the lower one exhibits antiferromagnetic behavior. With pressure both transitions shift towards lower temperatures. Around 1.5 GPa the upper magnetic transition completely disappears and only the lower persists up to ∼4 GPa. The electrical resistivity measured up to 8.0 GPa shows that structural transformation occurs in UPt under pressure