Novel magnetic behavior affected by multipolar interactions in the tetragonal RB2C2 compounds (R=Tb, Dy and Ho)

The present report reviews the experimental works on the tetragonal RB2C2 compounds performed based on our interest in novel magnetic properties strongly affected by multipolar interactions by means of magnetization, specific heat, neutron diffraction and 161Dy Moessbauer experiments. Our finding of an antiferroquadrupolar (AFQ) ordering below TQ=24.7 K in DyB2C2 triggered the successive findings as follows. HoB2C2, unexpectedly, shows an AFQ transition at TQ=4.5 K below an antiferromagnetic transition (AFM) transition at TN=5.9 K. An AFM compound TbB2C2 with TN=22.0 K shows an anomalous increase of susceptibility below TN, and the magnetic structure is a peculiar one among the RB2C2 compounds. Furthermore, it is confirmed by neutron diffraction of the single crystal that an AFQ ordered phase is induced by magnetic fields. (author)