μSR study of magnetism in Co-based honeycomb materials BaCo₂(PO₄)₂and BaCo₂(AsO₄)₂

In the intervening years since Kitaev proposed his exactly solvable model, condensed matter physicists have been working to discover materials in which Kitaev-like interactions exist. In recent years, the scope of candidate Kitaev materials has been expanded to include 3d transition metals such as Co²⁺, which has moderately strong S-O coupling. BaCo₂(XO₄)₂ (X = P, As) are examples of such materials, where the Co²⁺ ions form a highly frustrated, undistorted honeycomb lattice of Co2+ that are well separated by Ba and X layers. While these materials are isostructural, bulk property and neutron diffraction measurements show that they adopt very different magnetic ground states. Neutron diffraction of BaCo₂(AsO₄)₂ reveals not one, but two distinct short range ordered states. BaCo₂(AsO₄)₂, on the other hand, adopts long range order, but has shown evidence of being a field-induced, Kitaev quantum spin liquid. In this presentation, I will show muon spin relaxation data that show insight into the magnetism of each of these materials.