Characterization of the spin-1/2 linear-chain ferromagnet Trippkeite (CuAs₂O₄)

The magnetism of one-dimensional antiferromagnetic spin S=1/2 chains which feature nearest and next-nearest neighbor intrachain spin exchange interaction is of particular interest. Frustration of the intrachain spin exchange can bring about new and unusual magnetic groundstates. Here we describe the magnetic properties of the mineral Trippkeite with chemical composition CuAs₂O₄. The crystal structure of CuAs₂O₄ contains CuO₂ ribbon chains with strong nearest-neighbour intrachain and weaker antiferromagnetic next-nearest spin exchange interaction. CuAs₂O₄ represents he first system of the class of ribbon chain magnets which exhibits ferromagnetic ordering at low temperatures.