Optimized Flux Single-Crystal Growth of the Quantum Spin Liquid Candidate NdTa7O19 and Other Rare-Earth Heptatantalates, ErTa7O19 and GdTa7O19
来源：ACS Publications
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 NdTa7O19, the first quantum spin liquid candidate on a triangular spin-lattice with dominant Ising-like spin correlations. Purple NdTa7O19 single crystals with hexagonal morphology were successfully grown by using a K2Mo3O10–B2O3 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, NdTa7O19 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, ErTa7O19 and GdTa7O19, were also grown, and their magnetic properties investigated. The magnetic anisotropy of ErTa7O19 closely resembles that of isostructural NdTa7O19, indicating the possibility of a similar exotic magnetic ground state. In contrast, GdTa7O19 shows paramagnetic behavior, consistent with previous results obtained for polycrystalline samples.
In this study, nearly single-phase polycrystalline NdTa7O19 was successfully prepared. A previously reported solid-state method was optimized, resulting in a 98(1) wt % of the main phase, which was used as a starting material for flux growth of NdTa7O19 single crystals of predominantly hexagonal, plate-like morphologies with lateral sizes up to 3.5 mm and thicknesses up to 2 mm─the largest NdTa7O19 single crystals reported to date. The flux method presented here was further employed to grow single crystals of two other novel rare-earth heptatantalates, ErTa7O19 and GdTa7O19. The composition and morphology of all newly grown crystals were characterized by powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction (SCXRD) as well as scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). Furthermore, magnetic susceptibility measurements were employed to investigate the magnetic anisotropy.