Néel-type antiferromagnetic order and magnetic field-temperature phase diagram in the spin- 12 rare-earth honeycomb compound YbCl3

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 α-RuCl3. Here we propose the monoclinic YbCl3 with a Yb3+ honeycomb lattice for the exploration of Kitaev physics. We perform thermodynamic, ac susceptibility, angle-dependent magnetic torque, and neutron diffraction measurements on YbCl3 single crystal. We find that the Yb3+ ion exhibits a Kramers doublet ground state that gives rise to an effective spin Jeff=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 Yb3+ spins lie in the ac plane with an angle of 16(11)∘ 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 nonmonotonically under the out-of-plane magnetic fields, suggesting a reduced spin dimensionality. Together with the strong in-plane magnetic anisotropy and the reduced order moment 0.8(1) μB at 0.25 K, all indicate that YbCl3 could be a two-dimensional spin system to proximate the Kitaev physics.