NMR and local-density-approximation evidence for spiral magnetic order in the chain cuprateLiCu2O2

We report on ${}^{6,7}\mathrm{Li}$ nuclear magnetic resonance measurements of the spin-chain compound ${\mathrm{LiCu}}_2{\mathrm{O}}_2$ in the paramagnetic and magnetically ordered states. Below $24\mathrm{K}$ the NMR line shape shows a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments. ${}^7\mathrm{Li}$ NMR reveals strong phason-like dynamical fluctuations extending well below $24\mathrm{K}$. A series of phase transitions at 24.2, 22.5, and $9\mathrm{K}$ is observed. Local density approximation based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.