Helicoidal magnetic order in the spin-chain compound NaCu2O2 -: art. no. 140402

We report susceptibility, specific heat, and neutron diffraction measurements on NaCu2O2, a spin-1/2 chain compound isostructural to LiCu2O2, which has been extensively investigated. Below 12 K, we find a long-range ordered, incommensurate magnetic helix state with a propagation vector similar to that of LiCu2O2. In contrast to the Li analog, substitutional disorder is negligible in NaCu2O2. We can thus rule out that the helix is significantly influenced by impurities. A spin Hamiltonian with frustrated longer-range exchange interactions provides a good description of both the ordered state and the paramagnetic susceptibility.