Quantum magnetisms in uniform triangular lattices Li2AMo3O8 (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 A Mo 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 ( μ SR) 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 μ SR 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.