Antiferromagnetic ordering and metamagnetism in PrCuSi: Evidence for a tricritical point

A variety of physical properties measured on the hexagonal rare-earth intermetallic compound PrCuSi are presented. We provide compelling evidence for antiferromagnetic ordering at T _N = 5.1 K in this compound, in contrast to the former claim of ferromagnetic ordering at 14 K. The antiferromagnetic order is, however, found to be unstable in applied magnetic fields, becoming ferromagnetic beyond a metamagnetic transition at a field of 0.7 T at 2 K. It is argued that the magnetism in PrCuSi has the ingredients of a tricritical phase transition at the intersection of paramagnetism, ferromagnetism, and antiferromagnetism.