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

Abstract

The honeycomb antiferromagnet BaCo2⁢(AsO4)2, in which small in-plane magnetic fields (𝐻⁡1≈0.26 T and 𝐻⁡2≈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 3⁢𝑑 element Co2+. Here, we report on the change in the transition temperature 𝑇𝑁 and the critical fields 𝐻⁡1 and 𝐻⁡2 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 𝐻⁡1 is increased with hydrostatic pressure, i.e., the antiferromagnetic state is stabilized, whereas 𝐻⁡2, 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.