Anomalous antiferromagnetic properties of the tetragonal compound, TbB2C2

Magnetic properties of the tetragonal compound TbB2C2 were investigated by means of specific heat, magnetization and neutron diffraction measurements. TbB2C2 is an antiferromagnetic with T-N = 21.7 K. However, the magnetic susceptibility exhibits no cusp-like anomaly but shows an increase below T-N. In the ground state, the magnetic moments of Tb lie in the basal c-plano and the magnetic structure can be described with the propagation vectors of the dominant component of k = [0 1 1/2] with the weak components of k' = [0 0 1/2]. In addition, there also exists a weak longitudinal sinusoidal moment-modulation type component which is represented by k(L) = [1 +/- delta +/- delta 0], where delta = 0.13. Although the fundamental magnetic correlation in RB2C2 is [1 0 0]-type the dominant component in the ground state of TbB2C2 is k = [0 1 1/2]-type.