First-order-like antiferromagnetic transition and field-induced antiferroquadrupolar transition in terbium palladium bronze TbPd ₃S₄

Specific heat and magnetic susceptibility measurements were performed on single crystalline TbPd₃S₄, as well as neutron powder diffraction experiments in various magnetic fields. The sharp peak in the specific heat at the Néel temperature T_N = 2.55 K and the discontinuous decrease in the magnetic susceptibility at T_N suggested that a first-order antiferromagnetic (AFM) transition was occurring. Field-induced phases were found above about 0.5 T. Since the phase boundary between the field-induced and paramagnetic phases in the B - T phase diagram is of the "re-entrant" type, the field-induced phase can be concluded to be antiferroquadrupolar (AFQ) ordering one. The appearance of a canted magnetic structure above 0.5 T supports the existence of field-induced AFQ ordering. In addition to a magnetic interaction, a quadrupolar or higher multipolar interaction is crucial for determining the magnetic ground state in TbPd ₃S₄. The first-order-like AFM transition is caused by these multipolar interactions.