Neutron diffraction study of the nuclear and magnetic structure of the quasi-one-dimensional compound ${\mathrm{CuSiO}}_3$ around $T_N=8\mathrm{}\mathrm{K}$

We investigated the nuclear and magnetic structure of ${\mathrm{CuSiO}}_3$ by neutron powder diffraction methods at room temperature and around $T_N=8\mathrm{}\mathrm{K}.$ With decreasing temperature the lattice parameters showed, similar to ${\mathrm{CuGeO}}_3,$ decreasing a and b parameters and a slightly increasing c parameter down the chain direction. Below the second order phase transition at $T_N$ we observed for ${\mathrm{CuSiO}}_3$ the appearance of a small set of magnetic superstructure reflections; the determined antiferromagnetic order can be described by a commensurate propagation vector of $\mathbf{q}=(1/2,0,1/8)$ with respect to the chemical Pbmm unit cell. From the long modulation along the chain a ferromagnetic next neighbor magnetic exchange is deduced, whereas next nearest neighbor coupling is expected to be antiferromagnetic.