Antiferroquadrupolar Ordering and Magnetic Properties of the Tetragonal DyB_<b>2</b>C_<b>2</b>Compound

Abstract

Magnetic properties were investigated on a single-crystalline DyB 2 C 2 compound with the tetragonal structure. Spontaneous magnetizations appear along the a- and [1 1 0]-directions below T C =15.3 K. A very small shoulder is observed only along the c -axis at T Q =24.7 K, although large λ-type anomalous specific heats are observed at T C and T Q . There exists a large magnetic anisotropy in the tetragonal basal plane which is observed in magnetization processes below T C . Neutron powder diffraction experiments reveal that magnetic reflections are observed only below T C . In the magnetically ordered phase, the Dy moments are arranged to be perpendicular to neighbors along the c -axis. The results are well interpreted by postulating that the phase between T C and T Q is an antiferroquadrupolar ordered one. DyB 2 C 2 is a novel compound with a high antiferroquadrupolar ordering temperature of 24.7 K.