Crystal growth, magnetic and magnetocaloric properties of Jeff = 1/2 quantum antiferromagnet CeCl3

We report growth of high-quality single crystals of CeCl₃ using a modified Bridgman-Stockbarger method in an infrared image furnace. The grown crystals are characterized using single-crystal(powder) x-ray diffraction, Laue x-ray diffraction, Raman spectroscopy, magnetization, and heat-capacity probes. CeCl₃ crystallizes in a hexagonal structure (P6₃/m) with a weak trigonal distortion (P3̄). The Raman spectrum at 300 K shows five clearly resolvable phonon modes at 106.8, 181.2, 189, 213, and 219.70.16em0excm^-1. The magnetic susceptibility along H∥4pt0exc4pt0ex(χ^∥) and H⊥c4pt0ex(χ^⊥) axis is measured as a function of temperature and magnetic field. χ^⊥ exhibits a broad peak centered around 50 K; χ^∥, in comparison, shows a monotonic Curie-like increase upon cooling and is about two orders of magnitude larger in size. This anisotropic behavior with qualitatively different temperature dependences shown by χ^∥ and χ^⊥ is explained using the crystal field theory. The crystal field in CeCl₃ splits the $J=5/2$ manifold of Ce³⁺ into three Kramers doublets with |5/2,±5/2 as the ground state, and |5/2,±1/2 at energy E₁=61 K, and |5/2,±3/2 at E₂=218 K as the first and second excited states, respectively. Accordingly, M(H) at 2 K along H⊥c is small and shows a linear variation, whereas M(H) along H∥c saturates readily (easy axis) to the expected value. In the specific heat, no magnetic ordering could be seen down to 2 K. However, in nonzero fields the low-temperature specific heat changes dramatically, showcasing a peak at 2.5 K under a moderate field of 30 kOe. The weak Ce-Ce exchange, large Ce moment in the crystal-field ground state, and huge anisotropy are all ingredients for realizing a high magnetocaloric effect. Indeed, measurements at low temperatures reveal a maximum entropy change of ${-}{{Δ}}{S}4f{≈}23{{4pt}{0ex}}±{}1{{4pt}{0ex}}J{{4pt}{0ex}}{{4pt}{0ex}}K{g}^{{-}1}{{4pt}{0ex}}{K}^{{-}1}$ near 2.5 K in the field ranging from 50 to 60 kOe. These values are comparable to some of the best known Gd-based magnetocaloric materials, signifying the potential of $CeC{l}₃$ as a magnetic coolant.