Chemical tuning of a honeycomb magnet through a critical point

BaCo₂(AsO₄)₂, or BCAO, has seen extensive study since its initial identification as a proximate Kitaev quantum spin liquid (KQSL) candidate. Although recent studies suggest its magnetic ground state is better described by the highly anisotropic XXZ-J₁-J₃ model, the ease with which magnetic order is suppressed with the application of a small in-plane magnetic field indicates proximity to a spin liquid phase. Upon chemical tuning via partial arsenic substitution with vanadium, BaCo₂(AsO₄)_2-2x(VO₄)_2x, we show an initial suppression of long-range order in the BCAO system to T = 2.58 K, followed by the introduction of increased spin freezing at higher substitution levels. Between these two regions at x = 0.10, the system is shown via AC and DC susceptibility, Raman scattering spectroscopy, and heat capacity measurements to pass through a critical point where no phase transition is apparent down to T = 0.40 K. At this level of substitution, the competing nearest-neighbor J₁ and third nearest-neighbor J₃ interactions apparently become more balanced, producing a more complex magnetic ground state, likely stabilized by quantum fluctuations. This study shows how slight compositional change in magnetically-frustrated materials may be leveraged to enhance ground-state degeneracy and potentially realize a quantum spin liquid state.