Bose-Einstein condensation of triplons in Ba3 Cr2 O8

By performing heat-capacity, magnetocaloric effect, torque magnetometry, and force magnetometry measurements up to 33 T, we have mapped out the T-H phase diagram of the S=1/2 spin dimer compound Ba3 Cr2 O8. We found evidence for field-induced magnetic order between Hc1 =12.52 (2) T and Hc2 =23.60 (5) T, with the maximum transition temperature Tc ∼2.7 K at H∼18 T. The lower transition can likely be described by Bose-Einstein condensation of triplons theory, and this is consistent with the absence of any magnetization plateaus in our magnetic torque and force measurements. In contrast, our measurements uncovered magnetic field irreversibility associated with a symmetric specific heat versus temperature near Hc2 suggesting that the upper transition is first order.