Anisotropic magnetic properties of TbNi2B2C single crystals

Magnetic and transport properties of single crystals of TbNi2B2C have been investigated by ac susceptibility, de magnetization, specific heat, and resistance measurements. The compound shows highly anisotropic magnetic properties which come about as a result of the Tb magnetic moments lying predominantly in the ab plane. The ac susceptibility and low-field de magnetization measurements indicate the presence of two magnetic transitions; one due to the antiferromagnetic (AFM) ordering of the Tb moments around 15 K, and another at 5 K, which we believe is due to a spin reorientation of the Tb moments. The resistivity (rho(ab)) measurements show a sharp decrease in the resistance at 15 K but contain no observable features corresponding to the lower-temperature transition. The compound does not show superconductivity above 300 mK. Specific heat at low temperatures shows a large h-type anomaly at 13.8 K in addition to the anomalies associated with the AFM ordering of the Tb moments at 15 K (T-AF) and the spin reorientation at 5 K. Magnetization (M) and rho(ab)(T) measurements indicate a decrease in T-AF as a function of applied field (H) for H parallel to ab, whereas for H parallel to c, T-AF is independent of field. The M-H isotherms at 2 K show that for H parallel to ab the compound goes through a series of temperature-dependent metamagnetic states before finally saturating into a ferromagnetic state for H>21 kOe. For H parallel to c the compound shows a linear M-H behavior expected for a normal AFM compound. The rho(ab)(H) measurements show anomalies due to the metamagnetic transitions and a large negative magnetoresistance above 21 kOe for H parallel to ab