Sharp quantum phase transition in the frustrated spin-1/2 / 2 Ising chain antiferromagnet CaCoV2O7 2 O 7

We report on a quantum critical behavior in the quasi-1D spin-1/2 / 2 zigzag frustrated chain antiferromagnet CaCoV2O7, 2 O 7 , induced by an applied magnetic field. Below TN N = 3.3 . 3 K our zero-field neutron diffraction studies revealed the up-up-down-down spin structure, stabilized by an order-by-disorder phenomenon. At base temperature, the magnetic order is suppressed by an applied magnetic field (B), B ), inducing a transition into a quantum paramagnetic state at Bc c = 3 T, as revealed by both neutron diffraction and ESR data. The transition exhibits an unusually sharp phase boundary with the critical exponent phi = 0.164(3) . 164(3) approximate to 1/6, / 6, in contrast to the earlier experimental observations for uniform spin-1/2 / 2 chain systems. Such a sharp QPT is anticipated due to a rare combination of spin-orbit coupling and competing NN and NNN exchange interactions J 1 and J 2 of the zigzag spin chain.