Magnetic anisotropy and weak ferromagnetism of single-crystalTbNi2B2C

The anisotropic magnetization M(T) of single-crystal ${\mathrm{TbNi}}_2$ ${\mathrm{B}}_2$C is reported as a function of applied magnetic field (H) for temperatures T from 2 to 300 K and with H parallel and perpendicular to the c axis (H∥c and H⊥c). In low field (H≤100 G) ${\mathrm{TbNi}}_2$ ${\mathrm{B}}_2$C orders antiferromagnetically at Néel temperature ${\mathit{T}}_{\mathit{N}}$=(14.9±0.1) K. Weak ferromagnetic (WF) behavior is found for T≤8 K and H≤10 kG. Both phase transitions are also detected in zero-field in-plane resistivity ${\mathrm{\rho }}_{\mathit{ab}}$(T) measurements. In contrast, previous low-field M(T,H) data showed antiferromagnetic ground states for (Gd,Dy,Ho,Er,Tm)${\mathrm{Ni}}_2$ ${\mathrm{B}}_2$C crystals. The origin of the WF ordering, given the point symmetry (4/mmm) of the ${\mathrm{Tb}}^{+3\mathrm{}}$ ions, is addressed together with the observed in-plane anisotropy in the high-field magnetization. Possible reasons for the absence of superconductivity above 2 K in ${\mathrm{TbNi}}_2$ ${\mathrm{B}}_2$C are also discussed. Finally, a partial H-T magnetic phase diagram of ${\mathrm{TbNi}}_2$ ${\mathrm{B}}_2$C is presented for H∥[110] and aspects of the similar H-T diagram for H∥[100] are discussed. © 1996 The American Physical Society.