  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 of 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 of 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 with hydrostatic
pressure, whereas H2, which was previously associated with a transition into a
proposed Kitaev spin liquid state, decreases with increasing pressure. These
results put constraints on the magnetic models that are used to describe the
low-temperature magnetic properties of BaCo2(AsO4)2.
