Spin waves and magnetic interactions inLiCu2O2

The quasi-one-dimensional helimagnet $\mathrm{Li}{\mathrm{Cu}}_2{\mathrm{O}}_2$ was studied by single crystal inelastic neutron scattering. The dispersion relation of spin wave excitations was measured in the vicinity of the principal magnetic Bragg reflection. A spin wave theoretical analysis of the data yields an estimate of the relevant exchange constants and explains the mechanism of geometric frustration that leads to helimagnetism. It is found that the simple antiferromagnetic $J_1\text{−}{J}_2$ model that was previously proposed is inadequate for $\mathrm{Li}{\mathrm{Cu}}_2{\mathrm{O}}_2$. The experimental findings are generally in a qualitative agreement with first principles calculations of [A. A. Gippius, E. N. Morozova, A. S. Moskvin, A. V. Zalessky, A. A. Bush, M. Baenitz, H. Rosner, and S.-L. Drechsler, Phys. Rev. B 70, 020406 (2004)], though certain important discrepancies remain to be explained.