Quantum magnetisms in uniform triangular lattices Li(2)AMo(3)O(8) (A = In, Sc)

Molecular based spin-1/2 triangular lattice systems such as LiZn(2)Mo(3)O(8) have attracted research interest. Distortions, defects, and intersite disorder are suppressed in such molecular-based magnets, and intrinsic geometrical frustration gives rise to unconventional and unexpected ground states. Li(2)AMo(3)O(8) (A = In or Sc) is such a compound where spin-1/2 Mo(3)O(13) clusters in place of Mo ions form the uniform triangular lattice. Their ground states are different according to the A site. Li(2)InMo(3)O(8) undergoes conventional 120° long-range magnetic order below T(N) = 12 K whereas isomorphic Li(2)ScMo(3)O(8) exhibits no long-range magnetic order down to 0.5 K. Here, we report exotic magnetisms in Li(2)InMo(3)O(8) and Li(2)ScMo(3)O(8) investigated by muon spin rotation (μSR) and inelastic neutron scattering (INS) spectroscopies using polycrystalline samples. Li(2)InMo(3)O(8) and Li(2)ScMo(3)O(8) show completely different behaviors observed in both μSR and INS measurements, representing their different ground states. Li(2)InMo(3)O(8) exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the 120° spin structure. In contrast, Li(2)ScMo(3)O(8) undergoes short-range magnetic order below 4 K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions.