The nature of crystal field excitations dominated by field induced quantum fluctuations in Co2+ stacked-honeycomb antiferromagnet: Ba2Co(PO4)2

We have synthesized Co2+ stacked-honeycomb antiferromagnet compound Ba2Co(PO4)2 and explored detailed structural and magnetic compound for the first time for which microscopic evidence of Co2+ crystal field excitations (CFE) is unknown to date. Co2+ can shows several spin states including high-spin, intermediate-spin, and low-spin state, therefore the CEF energy levels will give proper information about the accurate spin-state of Co2+. For the proposed Co2+ compound, through a combination of magnetic susceptibility, specific heat, and 31P NMR studies, the temperature-magnetic-field phase diagram associated with this long range magnetic ordering at TN = 3~K has been mapped out. A low-temperature field-induced spin-flop transition below TN is found to occur at an applied field (B) of 3 Tesla. The temperature dependent susceptibility curve also shows pronounced broad peak at around Tmax = 4 K, characteristics of the short-range magnetic ordering. The combined results of heat capacity and susceptibility of Ba2Co(PO4)2 stabilize a magnetic field induce phase transition. Interestingly, the field tuned non-thermal parameter is used to drive the long-range-ordering state towards more quantum disorder state, where a quantum critical point (QCP) is evident at critical field about ~3 T on H-T phase diagram.