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 hea t, and resistance measurements. The compound shows highly anisotropic magnetic properties which come about as a result of the Tb magnetic mo ments lying predominantly in the ab plane. The ac susceptibility and l ow-field de magnetization measurements indicate the presence of two ma gnetic transitions; one due to the antiferromagnetic (AFM) ordering of the Tb moments around 15 K, and another at 5 K, which we believe is d ue to a spin reorientation of the Tb moments. The resistivity (rho(ab) ) measurements show a sharp decrease in the resistance at 15 K but con tain no observable features corresponding to the lower-temperature tra nsition. The compound does not show superconductivity above 300 mK. Sp ecific 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. Magnetiza tion (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 para llel 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 tempe rature-dependent metamagnetic states before finally saturating into a ferromagnetic state for H>21 kOe. For H parallel to c the compound sho ws a linear M-H behavior expected for a normal AFM compound. The rho(a b)(H) measurements show anomalies due to the metamagnetic transitions and a large negative magnetoresistance above 21 kOe for H parallel to ab.