Single-crystal growth, crystallography, magnetic susceptibility, heat capacity, and thermal expansion of the antiferromagnetic S=1 chain compound CaV2O4

The compound CaV2O4 contains V+3 cations with spin S=1 and has an orthorhombic structure at room temperature containing zigzag chains of V atoms running along the c axis. We have grown single crystals of CaV2O4 and report crystallography, static magnetization, magnetic susceptibility chi, ac magnetic susceptibility, heat capacity C-p, and thermal expansion measurements in the temperature T range of 1.8-350 K on the single crystals and on polycrystalline samples. An orthorhombic-to-monoclinic structural distortion and a long-range antiferromagnetic (AF) transition were found at sample-dependent temperatures T-S approximate to 108-145 K and T-N approximate to 51-76 K, respectively. In two annealed single crystals, another transition was found at approximate to 200 K. In one of the crystals, this transition is mostly due to V2O3 impurity phase that grows coherently in the crystals during annealing. However, in the other crystal the origin of this transition at 200 K is unknown. The chi(T) shows a broad maximum at approximate to 300 K associated with short-range AF ordering and the anisotropy of chi above T-N is small. The anisotropic chi(T -> 0) data below T-N show that the (average) easy axis of the AF magnetic structure is the b axis. The C-p(T) data indicate strong short-range AF ordering above T-N, consistent with the chi(T) data. We fitted our chi data by a J(1)-J(2) S=1 Heisenberg chain model, where J(1)(J(2)) is the (next)-nearest-neighbor exchange interaction. We find J(1)approximate to 230 K and surprisingly, J(2)/J(1)approximate to 0 (or J(1)/J(2)approximate to 0). The interaction J(perpendicular to) between these S=1 chains leading to long-range AF ordering at T-N is estimated to be J(perpendicular to)/J(1)greater than or similar to 0.04.