Crystal growth, magnetic and magnetocaloric properties of 𝐽�eff = 1/2 quantum antiferromagnet CeCl3

Abstract

We report growth of high-quality single crystals of CeC⁢l3 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. CeC⁢l3 crystallizes in a hexagonal structure (𝑃⁢63/𝑚) with a weak trigonal distortion (𝑃⁢‾3). The Raman spectrum at 300 K shows five clearly resolvable phonon modes at 106.8, 181.2, 189, 213, and 219.7c⁢m−1. The magnetic susceptibility along 𝐻∥𝑐⁡(𝜒∥) and 𝐻⁢⊥⁢𝑐⁡(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 CeC⁢l3 splits the 𝐽=5/2 manifold of C⁢e3+ 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⁢𝑆4⁢𝑓≈23±1⁢JK⁢g−1K−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⁢l3 as a magnetic coolant.