Exploring the disordered magnetic ground state and spin dynamics in the honeycomb oxide Na₃Cu₂SbO₆

Copper-based oxide materials have emerged as promising candidates for exploring low-dimensional magnetism due to their unique electronic and magnetic properties. Among these, Na₃Cu₂SbO₆ stands out as a particularly intriguing compound for both experimental and theoretical investigations, owing to its distorted honeycomb lattice structure and the presence of spin-gap behavior. In this study, we conducted comprehensive magnetization, heat capacity, and muon spin relaxation (μSR) measurements on the layered honeycomb oxide Na₃Cu₂SbO₆ to elucidate its magnetic ground state and probe the complex spin dynamics in detail. Na₃Cu₂SbO₆ crystallizes in a C-centered monoclinic structure with the space group C2/m (No. 12). Magnetization and specific heat measurements reveal the absence of long-range magnetic ordering down to 2 K. Furthermore, specific heat data exhibit a Schottky-like anomaly at low temperatures, indicative of short-range magnetic correlations, while no evidence of long-range ordering is observed. The temperature dependence of the muon spin relaxation rate λ suggests the presence of spin fluctuations or a quantum-disordered ground state in Na₃Cu₂SbO₆. The absence of oscillations in the zero-field (ZF) μSR spectra further confirms the lack of long-range magnetic order in the material. Longitudinal field (LF) μSR experiments provide additional insights, revealing that the spin fluctuations persisting at low temperatures are dynamic in nature. Our findings indicate that the disordered and fluctuating magnetic ground state in Na₃Cu₂SbO₆ can be attributed to magnetic frustration arising from competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions along the b axis within the ab plane. These results highlight the rich magnetic behavior of Na₃Cu₂SbO₆ and its potential as a model system for studying low-dimensional magnetism and quantum spin phenomena.