NMR and local-density-approximation evidence for spiral magnetic order in the chain cuprate LiCu2O2

Abstract

We report on Li nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below 24 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. Li NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. A series of phase transitions at 24.2, 22.5, and 9 K is observed. Local density approximation based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.