Rare-earth tri-iodides ($R{\mathrm{I}}_3$) are a series of two-dimensional van der Waals (vdW) magnetic materials comprising a layered honeycomb structure. Both the growing interest in vdW magnetic systems and the honeycomb layered structure of $R{\mathrm{I}}_3$ compounds, which is essential for realizing Kitaev physics, motivated us to grow high-quality single crystals of this series of materials and investigate their ground-state magnetic properties. Here, we report the crystal growth, magnetic, and thermodynamic properties of large (centimeter-sized), high-quality crystals of $R{\mathrm{I}}_3$ compounds. The crystal growth uses the physical vapor transport method via self-transport reaction using iodine as a transporting agent. The growth parameters are meticulously reported. The crystallographic parameters are obtained using single-crystal x-ray diffraction. While the $R{\mathrm{I}}_3$ compounds for the lighter rare earths ($R$ = La and Ce) crystallize with an orthorhombic (Cmcm) structure, the structure for the heavier rare earths is trigonal ( $R\overline{3}$ ), analogous to the extensively investigated Kitaev material $\alpha \text{−}{\mathrm{RuCl}}_3$. The density functional theory–based calculations are performed to obtain the eigenfrequencies/eigenvectors of the Raman-active phonon modes for both structure types and compared with the experimental Raman spectra of ${\mathrm{CeI}}_3$ (Cmcm) and ${\mathrm{HoI}}_3$ ( $R\overline{3}$ ). The magnetic behavior examined for the heavier rare-earth-based compounds indicates no signs of long-range magnetic ordering down to 2 K. However, signatures of short-range correlations are seen below 5 K, both in the magnetic susceptibility and specific heat of all the compounds.

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• Magnetic susceptibility
• Magnetism
• Quantum spin liquid
• Specific heat
• Honeycomb lattice
• van der Waals systems
• Crystal growth
• DFT+U
• Density functional calculations
• Magnetization measurements
• Raman spectroscopy
• X-ray diffraction