Exotic (anti)ferromagnetism in single crystals of Pr₆Ni₂Si₃

The ternary intermetallic compound, Pr₆Ni₂Si₃, is a member of a structure series of compounds based on a triangular structure where the number of Pr atoms in the prism cross section can be systematically varied. Pr₆Ni₂Si₃ contains two distinct Pr lattice sites which result in complex interactions between the magnetic ions. Extensive measurements of specific heat and magnetization on single-crystal samples indicate that Pr₆Ni₂Si₃ orders with both a ferromagnet and an antiferromagnet component, with ordering temperatures of 39.6 and ∼32 K, respectively. The ferromagnetic component ∥ c axis is accompanied by a large hysteresis, and the antiferromagnetic component ⊥ c axis is accompanied by a spin-flop-type transition. More detailed measurements, of the vector magnetization, indicate that the ferromagnetic and the antiferromagnetic order appear independent of each other. These results not only clarify the behavior of Pr₆Ni₂Si₃ itself but also of the other members of the structure series, Pr₅Ni₂Si₃ and Pr₁₅Ni₇Si₁₀.