Alkali metal rare-earth chalcogenide ARECh2 (A=alkali or monovalent metal, RE=rare earth, Ch=O, S, Se, Te), is a large family of quantum spin liquid (QSL) candidates we discovered recently. Unlike YbMgGaO4, most members in the family except for the oxide ones, have relatively small crystalline electric-field (CEF) excitation levels, particularly the first ones. This makes the conventional Curie-Weiss analysis at finite temperatures inapplicable and CEF excitations may play an essential role in understanding the low-energy spin physics. Here we considered an effective magnetic Hamiltonian incorporating CEF excitations and spin-spin interactions, to accurately describe thermodynamics in such a system. By taking NaYbSe2 as an example, we were able to analyze magnetic susceptibility, magnetization under pulsed high fields and heat capacity in a systematic and comprehensive way. The analysis allows us to produce accurate anisotropic exchange coupling energies and unambiguously determine a crossover temperature (∼25 K in the case of NaYbSe2), below which CEF effects fade away and pure spin-spin interactions stand out. We further validated the effective picture by successfully explaining the anomalous temperature dependence of electron spin resonance (ESR) spectral width. The effective scenario in principle can be generalized to other rare-earth spin systems with small CEF excitations.
@article{arxiv.2011.06274,
title = {Effective Magnetic Hamiltonian at Finite Temperatures for Rare Earth Chalcogenides},
author = {Zheng Zhang and Jianshu Li and Weiwei Liu and Zhitao Zhang and Jianting Ji and Feng Jin and Rui Chen and Junfeng Wang and Xiaoqun Wang and Jie Ma and Qingming Zhang},
journal= {arXiv preprint arXiv:2011.06274},
year = {2021}
}