Evidence of the quadrupolar ordering in DyPd₃S₄

By means of specific heat, magnetic susceptibility, and neutron powder diffraction experiments, we reinvestigated new samples of DyPd₃S₄ synthesized by an improved method. We found a new phase transition at T_Q = 3.4 K above the two magnetic transitions around 1 K, which was characterized by a distinct peak in the specific heat and only a small anomaly in the magnetic susceptibility. The neutron powder diffraction experiment demonstrated neither new magnetic reflections nor evidence of a change of the crystal structure below T_Q. It was furthermore found that the quartet crystalline-electric-field ground state is consistent with the result for the magnetic entropy deduced from the specific heat and that T_Q increases with the external magnetic field. These results strongly imply that the new phase transition at T_Q is due to antiferroquadrupolar ordering.