Magnetoelasticity and H-T phase diagram of TbNi2B2C

Abstract : We investigated the magnetoelastic and magnetic properties of single-crystal TbNi2B2C within the paramagnetic and ordered phases and along both a and c axes. The measured paramagnetic and gamma-parastriction susceptibilities are satisfactorily reproduced by the theoretical calculations based on crystalline electric field and molecular field approximations. The features of the gamma-symmetry lowering mode indicate a noticeable orthorhombic distortion within both paramagnetic and magnetically ordered regions. The H-T phase diagram (H||a) reveals a cascade of transformations that delineate the phase boundaries between a weak-ferromagnetic (WF) phase, an intermediate phase, and a paramagnetic saturated state. Interestingly, below 9 K and within the low-field regime, the phase boundary enclosing the WF state shows a reentrant behavior. Such a reentrance feature is associated with the presence of the net ferromagnetic component below TWF.