Impurity induced antiferromagnetic order in Haldane gap compound SrNi2-xMgxV2O8SrNi2-xMgxV2O8

The effect of nonmagnetic Mg2+Mg2+ doping in SrNi2V2O8SrNi2V2O8, a Haldane gap system with a disordered ground state, was investigated using DC magnetic susceptibility and heat capacity measurements in polycrystalline samples of SrNi2-xMgxV2O8SrNi2-xMgxV2O8 with x=0.03x=0.03, 0.05, 0.07, 0.1 and 0.14. The results clearly reveal that the substitution of Ni2+Ni2+(S=1)(S=1) ion by Mg2+Mg2+(S=0)(S=0) ion induces a magnetic phase transition with the ordering temperatures lying in the range 3.4–4.3 K, for the samples with lowest and highest value of x  . The intrachain exchange constant (J/kB)(J/kB) and the Haldane gap (Δ)(Δ) for all the compounds were estimated to be ∼98±2∼98±2 and 25 K, respectively, which are close to that of the undoped compound. The magnetization data further suggest that the compounds exhibit metamagnetic behavior below TNTN, supporting a picture of antiferromagnet with significant magnetic anisotropy and competing intrachain and interchain interactions.