Chemical tuning of a honeycomb magnet through a critical point

BaCo2⁢(AsO4)⁢2 (BCAO) has seen extensive study since its initial identification as a proximate Kitaev quantum spin liquid candidate. Thought to be described by the highly anisotropic XXZ-J1-J3 model, the ease with which magnetic order is suppressed in the system indicates proximity to a spin liquid phase. Upon chemical tuning via partial arsenic substitution with vanadium, we show an initial suppression of long-range incommensurate order in the BCAO system to T ≈ 3.0 K, followed by increased spin freezing at higher substitution levels. Between these two regions, at around 10% substitution, the system is shown to pass through a critical point where the competing J1/J3 exchange interactions become more balanced, producing a more complex magnetic ground state, likely stabilized by quantum fluctuations. Here, this state shows how slight compositional change in magnetically frustrated systems may be leveraged to tune ground state degeneracies and potentially realize a quantum spin liquid state.