Neutron scattering and muSR investigations of the spin liquid state with quenched disorder in LuCuGaO4

LuCuGaO4 has magnetic Cu2+ and diamagnetic Ga3+ ions distributed on a triangular bilayer and is suggested to undergo a spin-glass transition with T_g approximately 0.4 K. Using muSR and neutron scattering measurements, we show that at low temperature the spins form a short-range correlated state with spin fluctuations detectable over a wide range of timescales: at 0.05 K magnetic fluctuations can be detected in both the muSR time window and also extending beyond 7 meV in the inelastic neutron scattering response, indicating magnetic fluctuations spanning timescales between 1E-5 and 1E-10 seconds. The dynamical susceptibility scales according to the form χ''(ω)T^α, with α=1, throughout the measured temperature range (0.05 - 50 K). These effects are associated with quantum fluctuations and some degree of structural disorder in ostensibly quite different materials, including certain heavy fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond glasses. We therefore suggest LuCuGaO4 is an interesting model compound for the further examination of disorder and quantum magnetism.

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