Optimized Flux Single-Crystal Growth of the Quantum Spin Liquid Candidate NdTaO and Other Rare-Earth Heptatantalates, ErTaO and GdTaO.

Single crystals are essential for characterizing a wide range of magnetic states, including exotic ones such as quantum spin liquids. This study reports a flux method for growing single crystals of NdTaO, the first quantum spin liquid candidate on a triangular spin-lattice with dominant Ising-like spin correlations. Purple NdTaO single crystals with hexagonal morphology were successfully grown by using a KMoO-BO flux. With lateral sizes up to 3.5 mm and a thickness up to 2 mm, these are the largest dimensions reported to date. The chemical composition was confirmed by powder and single-crystal X-ray diffraction along with scanning electron microscopy with energy dispersive X-ray spectroscopy. Aiming for an accurate determination of the magnetic anisotropy and its effect on the magnetic properties, NdTaO crystals were additionally analyzed by magnetic susceptibility, revealing a substantial anisotropy without long-range magnetic ordering down to 2 K. Single crystals of two novel rare-earth heptatantalates, ErTaO and GdTaO, were also grown, and their magnetic properties investigated. The magnetic anisotropy of ErTaO closely resembles that of isostructural NdTaO, indicating the possibility of a similar exotic magnetic ground state. In contrast, GdTaO shows paramagnetic behavior, consistent with previous results obtained for polycrystalline samples.