Anisotropic magnetic ground state of single-crystalline quasi-two-dimensional honeycomb antiferromagnet YbI3

Abstract

Here we study YbI3, a quasi-two-dimensional layered material with Yb atoms arranged on an ideal honeycomb network of edge-sharing YbI6 octahedra, analogous to the low-temperature phase of 𝛼−RuCl3. High-quality single crystals of YbI3 are grown from Yb and I2 as starting precursors, using the vapor transport technique. The as-grown crystals are characterized by single-crystal x-ray diffraction, Raman spectroscopy, magnetization, and heat capacity probes. The crystal-field split ground state of Yb3+ in YbI3 is a well-isolated Kramers doublet with an effective moment 𝐽eff=1/2. On cooling, the low-temperature heat capacity of YbI3 reveals a broad peak at 𝑇1=0.95K due to short-range ordering of the Yb moments followed by a sharp peak at 𝑇2=𝑇𝑁=0.6K due to long-range ordering. The magnetic behavior is found to be weakly anisotropic with 𝜒∥>𝜒⊥, where 𝜒∥ and 𝜒⊥ refers to the in-plane (𝐻∥𝑎⁢𝑏) and out-of-plane (𝐻⁢⊥⁢𝑎⁢𝑏) susceptibilities. The 2 K isothermal magnetization saturates at ≈1.5µ𝐵/Yb3+ (in-plane) and ≈1µ𝐵/Yb3+ (out-of-plane), suggesting the anisotropy to be easy-plane type. The low-temperature heat capacity, well below 𝑇𝑁, is found to vary as 𝑇𝛼 with 𝛼≈2.5, indicating a possible unconventional magnetic ground state for YbI3.