Hydrostatic pressure effect on the Co-based honeycomb magnet BaCo2(AsO4)2

The honeycomb antiferromagnet BaCo2(AsO4)2, in which small in-plane magnetic fields (H1≈0.26 T and H2≈0.52 T at T=1.8 K<TN≈5.4 K) induce two magnetic phase transitions, has attracted attention as a possible candidate material for the realization of Kitaev physics based on the 3d element Co2+. Here, we report on the change in the transition temperature TN and the critical fields H1 and H2 of BaCo2(AsO4)2 with hydrostatic pressure up to ∼20 kbar, as determined from magnetization and specific heat measurements. Within this pressure range, a marginal increase in the magnetic ordering temperature is observed. At the same time, the critical fields are changed significantly (up to ∼25-35%). Specifically, we find that H1 is increased with hydrostatic pressure, i.e., the antiferromagnetic state is stabilized, whereas H2, which was previously associated with a transition into a proposed Kitaev spin-liquid state, decreases with increasing pressure. We discuss to what extent these results are compatible with suggested models with sizable third-nearest-neighbor exchange. Overall, the results put constraints on the magnetic models that are used to describe the low-temperature magnetic properties of BaCo2(AsO4)2.