Magnetic phase diagrams of a honeycomb cobaltate, BaCo₂(AsO₄)₂.

In the quest for potential Kitaev quantum spin liquid materials, BaCo₂(AsO₄)₂, a honeycomb cobaltate, has been highlighted as a promising contender. This assertion stems from the understanding that Co²⁺ ions (3d⁷) within an octahedral crystal environment, possessing a total spin S = 3/2 and an orbital angular momentum l_eff = 1, give rise to spin-orbit coupled j_eff = ½ doublet states. Nevertheless, recent experiments and theoretical calculations have raised questions regarding this assertion. Despite these uncertainties, evidence of continuum excitations resembling spinon excitation has been reported. In this work, we explored the characteristics of magnetic phases under both in-plane and out-of-plane magnetic fields through various experimental methods. Our findings confirm multiple magnetic phases with saturation field less than 1 T with in-plane fields, consistent with prior research. Remarkably, with out-of-plane magnetic fields, we discovered a new sequence of magnetic phase transitions and observed that an exceptionally high magnetic field is required to saturate magnetically the compound. We will talk about the implications of this strong magnetic anisotropy and specifics of some of these phases in this presentation.