Supercritical Hydrothermal Synthesis of Quasi-1D Chain Fluorocarbonate NaDy(CO3)F2 with Giant Rotating Magnetocaloric Effect

Strong quantum fluctuations and weak magnetic interactions in quasi-1D chain rare-earth (RE) magnets prevent long-range magnetic ordering, preserving magnetic entropy for ultra-low temperature refrigeration. Here, a Dy-based 1D chain carbonate, NaDy(CO3)F2, has been successfully grown into millimeter-level single crystals in supercritical hydrothermal conditions. Its crystal structures can be indexed by an orthorhombic unit cell (space group #62 Pnma) consisting of Dy-based zigzag chains, with the distribution of interchain Dy∙∙∙Dy distance (4.46 Å) larger than that of the intrachain Dy∙∙∙Dy distance (3.78 Å). The temperature-dependent magnetic susceptibility and specific heat measurements mark the onset of long-range magnetic ordering (TN ~ 2.4 K) for NaDy(CO3)F2. Moreover, its isothermal magnetic entropy change (ΔSmag) was examined based on millimetre-size single crystals. Our results unveil the direction-dependent magnetocaloric effect (MCE) of NaDy(CO3)F2, providing an excellent example of achieving a giant MCE via rotating the crystallographic direction of well-oriented single crystals.