Absence of magnetic ordering in the ground state of a SrTm2O4 single crystal

Abstract

We report on the first single crystal study of SrTm₂O₄. Magnetization measurements along the crystallographic axes of a nearly stoichiometric Sr_1.07(3)Tm_2.07(6)O_4.00(2) sample show either a positive or a negative Curie–Weiss temperature indicative of a competition between antiferromagnetic and ferromagnetic couplings. The field-dependent magnetization suggests an effective Zeeman splitting of the high-level J-multiplets above ∼8.3 T and that the paramagnetism may originate from only one of the two inequivalent Tm³⁺ crystallographic sites. Our single-crystal polarized neutron scattering and powder unpolarized neutron diffraction data show no evidence for either long- or short-range magnetic order even down to ∼65 mK. We reveal two TmO₆ octahedral distortion modes, i.e., one distortion is stronger than the other especially at low temperatures, which is attributed to different crystal fields of the two inequivalent octahedra. Therefore, the compound SrTm₂O₄ is unique and different from its brethren in the family of frustrated SrRE₂O₄ (RE = rare earth) magnets. We propose that crystal field anisotropy may dominate over weak dipolar spin interactions in SrTm₂O₄, thereby leading to a virtually non-ordered magnetic state.