One-dimensional (1D) or two-dimensional (2D) topologies between magnetic ions generally favour strong magnetic anisotropy and offer exotic fundamental states and other phenomena such as field-induced transitions, quantum tunnelling magnetisation and/or magnetisation steps with potential applications for high-density storage. We have prepared BaCo2As2O7 and BaCo2(As3O6)2 compounds with 1D chains and magnetisation plateaus. The purpose of this proposal is to study the magnetic structure as a function of field. The use of WISH will provide a complete characterisation of the magnetic structures of these compounds. WISH is needed due to the complex incommensurate structure (BaCoAs2O7) and big unit cell (BaCo2(As3O6)2•2H2O) of the compounds, requiring good resolution and long d-spacing range.