4f instability and elastic properties in the metal system TmS in high magnetic fields - art. no. 184434

We have made an investigation of the elastic properties of TmS in high magn etic fields. A pronounced softening was observed in elastic constants C-11 and (C-11 - C-12)/2 at low temperatures, while no softening was observed in C-44. An analysis based on crystalline electric field splitting of Tm ions indicates that ferroelectric quadrupolar interactions among quadrupolar mo ments with Gamma (3) symmetry developed at low temperatures. Two distinct a nomalies in C-11 were found in magnetic fields. We propose an (H-T) phase d iagram based on present and former results. This phase diagram implies that a field-induced ferromagnetic quadrupolar transition may occur in addition to an antiferromagnetic transition. Furthermore. the bulk modulus C-B exhi bits a softening at low temperature, implying an instability of the 4f stat e in the Tm ions.