Atypical antiferromagnetic ordering in single crystalline quasi-2D honeycomb magnet YbI${}_3$

Abstract

Here, we study YbI${}_3$, a quasi-2D layered material with Yb atoms arranged on an ideal honeycomb network of edge-sharing YbI${}_6$ octahedra, analogous to the low-temperature phase of $\alpha -$RuCl${}_3$. High quality single crystals of YbI${}_3$ are grown from Yb and I as starting precursors, using the vapor transport technique. The grown crystals are characterized by single crystal x-ray diffraction, Raman spectroscopy, magnetization, and heat capacity probes. The crystal-field split ground state of Yb${}^{3+}$ in \Yb~ is a well-isolated Kramers doublet with an effective moment ${\mathrm{J}}_{\mathrm{eff}}=1/2$. Upon cooling, the low-temperature heat capacity of \Yb~ reveals a broad peak at ${\mathrm{T}}_1=0.95$~K due to short-range ordering of the Yb moments, followed by a sharp peak at ${\mathrm{T}}_2={\mathrm{T}}_{\mathrm{N}}=0.6$~K due to long-range ordering. The magnetic behavior is found to be weakly anisotropic with ${\chi }^{\parallel }>{\chi }^{\perp }$, where ${\chi }^{\parallel }$ and ${\chi }^{\perp }$ refers to the in-plane ($H\parallel ab$) and out-of-plane ($H\perp ab$) susceptibilities. The 2~K isothermal magnetization saturates at $\approx 1.5{\mu }_{\mathrm{B}}/Y{\mathrm{b}}^{3+}$ (in-plane) and $\approx 1{\mu }_{\mathrm{B}}/Y{\mathrm{b}}^{3+}$ (out-of-plane), suggesting the anisotropy to be easy-plane type. Low-temperature heat capacity, well below T${}_N$, is found to vary as T${}^{\alpha }$ with $\alpha \approx 2.5$, indicating a possible unconventional magnetic ground state for YbI${}_3$.

10 pages, 5 figures, Supplemental Material available on request