A Néel-type antiferromagnetic order in the spin 1/2 rare-earth honeycomb YbCl${}_3$

Abstract

Most of the searches for Kitaev materials deal with $4d/5d$ magnets with spin-orbit-coupled $J=1/2$ local moments such as iridates and $\hat{I}\pm$-RuCl${}_3$. Here we propose the monoclinic YbCl${}_3$ with a Yb${}^{3+}$ honeycomb lattice for the exploration of Kiteav physics. We perform thermodynamic, $ac$ susceptibility, angle-dependent magnetic torque and neutron diffraction measurements on YbCl${}_3$ single crystal. We find that the Yb${}^{3+}$ ion exhibits a Kramers doublet ground state that gives rise to an effective spin $J_{\text{eff}}=1/2$ local moment. The compound exhibits short-range magnetic order below 1.20 K, followed by a long-range Néel-type antiferromagnetic order at 0.60 K, below which the ordered Yb${}^{3+}$ spins lie in the $ac$ plane with an angle of 16(11)${}^{\circ }$ away from the $a$ axis. These orders can be suppressed by in-plane and out-of-plane magnetic fields at around 6 and 10 T, respectively. Moreover, the Néel temperature varies non-monotonically under the out-of-plane magnetic fields. The in-plane magnetic anisotropy and the reduced order moment 0.8(1) $\hat{I}{¼}_B$ at 0.25 K indicate that YbCl${}_3$ could be a two-dimensional spin system to proximate the Kitaev physics.

6 pages, 5 figures, updated version