Magnetism and ESR of the S-eff=1/2 antiferromagnet BaCo2(SeO3)(3 )center dot 3H(2)O with dimer-chain structure

We report the magnetism and ESR of the S-eff = 1/2 compound BaCo2(SeO3)(3) center dot 3H(2)O with dimer-chain structure. The magnetic susceptibility and heat capacity show that the compound is antiferromagnetically ordered at T-N = 7.6 K. The magnetization M(H) curve at 2 K presents a spin-flop transition within 2.6-3.0 T when the magnetic field is applied along the ab plane (H perpendicular to c), pointing to the easy axis-like anisotropy. In high magnetic field, the magnetization increases nearly linearly until saturation at about 22 T, indicating a classical-like behavior. The magnetization process can be described with the intradimer exchange J(1) = -20.0 K and interdimer exchanges J(2) = -14.6 K and J(3) = -6.2 K. Thus, BaCo2(SeO3)(3) center dot 3H(2)O is approximately a three-dimensional antiferromagnet, although structurally it contains dimer chains.