Neutron scattering study on the antiferroquadrupolar order of DyB₂C₂ under magnetic fields

Antiferroquadrupolar (AFQ) ordering in DyB₂C₂ has been investigated by means of neutron scattering under applied magnetic fields along [110] up to 10 T. In the AFQ ordered phase at 16 K, antiferromagnetic reflections indexed as 00 1/2 and 11 1/2 are induced by a magnetic field of 1 T. These induced magnetic reflections disappear at 2 T, and develop again, increasing in intensity with increasing field, above 3 T. As temperature increases, the integrated intensity at 4 T shows an anomalous decrease toward ∼13 K in addition to a disappearance at T_Q, while that at 8 T decreases normally toward T_Q. We observed this curious behaviour of the induced magnetic reflections within the AFQ ordered phase.