Possible field-induced antiferroquadrupolar ordered phase in HoB2C2

Magnetic properties were investigated on the single-crystalline HoB2C2 comp ound with the tetragonal structure. An antiferromagnetic (AFM) transition o ccurs at T-N = 5.8 K. At T-Q = 5.0 K, a spin-reorientation transition occur s, and spontaneous magnetization appears along the [1 0 0]- and [1 1 0]-axi s. The magnetization behavior below T-Q is well interpreted by postulating the magnetic structure similar to that of the antiferroquadrupolar (AFQ) or dering compound DyB2C2. Below T-Q the AFQ ordering coexists competitively w ith the AFM ordering. The pure AFQ ordered phase is confirmed only in the m agnetic fields applied along the [1 1 0]-axis. (C) 2000 Elsevier Science B. V. All rights reserved.