Spin dynamics and magnetic ordering in the quasi-one-dimensional S= 12 antiferromagnet Na2 CuSO4 Cl2

The S=12 quasi-one-dimensional antiferromagnet K2CuSO4X2(X=Cl, Br) exhibits peculiar Dzyaloshinskii-Moriya (DM) interactions that are uniform along its spin chains and antiparallel with respect to neighboring chains. This feature has received much attention recently because it leads to spin frustration, however, the spin dynamics around TN and magnetic structure have not been reported. Here we report magnetic behaviors of Na2CuSO4Cl2. The orthorhombic crystal structure of Na2CuSO4Cl2, which is identical to K2CuSO4X2, was verified. The results of the thermodynamic measurements suggest that this compound has moderately strong intra- and interchain interaction for investigation of the spin state around TN. The inelastic neutron scattering and muon spin relaxation and rotation measurements reveal the presence of a two-spinon continuum, and below TN, the long-range order develops. However, the obtained critical exponent is β=0.18, which is not indicative of a three-dimensional magnetic system; instead, one-dimensional (1D) spin correlation likely affects the formation of magnetic ordering in Na2CuSO4Cl2. There is a possibility that Na2CuSO4Cl2 is a model compound for investigation of DM-induced frustration effects in a 1D quantum spin system.