High-Pressure Sequence of Ba3NiSb2O9 Structural Phases: New S = 1 Quantum Spin Liquids Based on Ni2+

Two new gapless quantum spin-liquid candidates with S = 1 (Ni2+) moments: the 6H-B phase of Ba3NiSb2O9 with a Ni2+-triangular lattice and the 3C phase with a Ni2/3Sb1/3-three-dimensional edge-shared tetrahedral lattice were obtained under high pressure. Both compounds show no magnetic order down to 0.35 K despite Curie-Weiss temperatures theta(CW) of -75.5 (6H-B) and -182.5 K(3C), respectively. Below similar to 25 K, the magnetic susceptibility of the 6H-B phase saturates to a constant value chi(0) = 0.013 emu/mol, which is followed below 7 K by a linear-temperature-dependent magnetic specific heat (C-M) displaying a giant coefficient gamma = 168 mJ/mol K-2. Both observations suggest the development of a Fermi-liquid-like ground state. For the 3C phase, the C-M proportional to T-2 behavior indicates a unique S = 1, 3D quantum spin-liquid ground state.