Figure 4: H−T phase diagram of Ba₂CoGe₂O₇.

AF to PM phase boundary is marked by peaks in ε(T), ε(H), dP(H)/dH, anomalies in τ/H versus T and direct current magnetic susceptibility (M/H) data (red squares, blue circles, purple triangles, orange diamonds, and black square, respectively). The crossover between field-induced quantum critical to gapped spin-polarized state at H>H_c is indicated by anomalies in ε(T) (T*, red squares above H_c see text). Dashed lines below and above H_c show the fit to the equation T_N∝|H−H_c|^1/2 and T*∝|H−H_c|^1/2, respectively.