Effective model for rare-earth Kitaev materials and its classical Monte Carlo simulation*

Abstract

Recently, the family of rare-earth chalcohalides were proposed as candidate compounds to realize the Kitaev spin liquid (KSL) [Chin. Phys. Lett. 38 047502 (2021)]. In the present work, we firstly propose an effective spin Hamiltonian consistent with the symmetry group of the crystal structure. Then we apply classical Monte Carlo simulations to preliminarily study the model and establish a phase diagram. When approaching to the low temperature limit, several magnetic long range orders are observed, including the stripe, the zigzag, the antiferromagnetic (AFM), the ferromagnetic (FM), the incommensurate spiral (IS), the multi- Q , and the 120° ones. We further calculate the thermodynamic properties of the system, such as the temperature dependence of the magnetic susceptibility and the heat capacity. The ordering transition temperatures reflected in the two quantities agree with each other. For most interaction regions, the system is magnetically more susceptible in the ab-plane than in the c-direction. The stripe phase is special, where the susceptibility is fairly isotropic in the whole temperature region. These features provide useful information to understand the magnetic properties of related materials.

Anisotropic exchange coupling and ground state phase diagram of Kitaev compound YbOCl

“…The absence of an inversion center between the next-nearest-neighbor (NNN) magnetic ions allows the second-order DM interaction. We have determined that the DM vector D ij is almost along the c axis [25]. The analysis gives the following low-energy effective spin Hamiltonian in YbOCl:…”

“…It is worth noting that the low-energy effective spin Hamiltonian adopted in this paper is a generic one and completely equivalent to the J-K-model. The two Hamiltonians can be converted to each other through coordinate transformation [25,27]. In this paper, we choose the generic low-energy effective spin Hamiltonian described in formula (1), as S z in the formula is consistent with the application of magnetic fields along the c axis of single crystals.…”

“…DM interaction has no effect on the phase diagram. Since the DM interaction in YbOCl is almost along the c axis [25], the sign of the DM interaction will only change the phase of the ground state wave function but not the magnetic moments in real space. More importantly, when the DM interaction | D i j | is less than 0.4 K, the phase diagram does not change much compared to the one without DM interaction.…”

“…The single-layer or few-layer flakes of DyOCl were successfully prepared by mechanical exfoliation [24]. Finally, the honeycomb lattice formed by magnetic ions in rare-earth chalcohalides is an undistorted hexagonal structure [21] that meets the symmetry required by the J-Kspin Hamiltonian model [25]. These features render rare-earth chalcohalide REChX as a promising candidate family for the exploration of Kitaev QSL. In this paper, we focus on magnetism at finite temperatures and the ground state phase diagram of YbOCl.…”