Ferrimagnetism and anisotropic phase tunability by magnetic fields in Na2Co2TeO6

Na2Co2TeO6 has recently been proposed to be a Kitaev-like honeycomb magnet. To assess how close it is to realizing Kitaev quantum spin liquids, we have measured magnetization and specific heat on high-quality single crystals in magnetic fields applied along high-symmetry directions. Small training fields reveal a weak but canonical ferrimagnetic behavior below 27 K, which suggests that the previously established zigzag antiferromagnetic order, with collinear moments pointing along the zigzag chains, must be supplemented by q=0 (e.g., Néel type in the absence of structural modulations) moment canting. Moderate fields in the honeycomb plane suppress the thermal transition at 27 K, and seem to partly reverse the moment canting when applied perpendicular to the zigzag chains. In contrast, out-of-plane fields leave the transition largely unaffected, but promotes another transition below 10 K, possibly also related to canting reversal. The magnetism in Na2Co2TeO6 is highly anisotropic and close to tipping points between competing phases.