NMR and LDA evidence for spiral magnetic order in the chain cuprate LiCu2O2

TL;DR

This study uses NMR and LDA calculations to demonstrate incommensurate spiral magnetic order in LiCu2O2, revealing complex magnetic phase transitions and strong in-chain frustration.

Contribution

It provides experimental NMR evidence combined with theoretical calculations showing spiral magnetic order and multiple phase transitions in LiCu2O2.

Findings

Incommensurate spiral magnetic order below 24 K

Multiple phase transitions at 24.2, 22.5, and 9 K

Large in-chain magnetic frustration leading to spiral order

Abstract

We report on {6,7}Li nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below T about 24 K the NMR lineshape presents a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments. {7}Li NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. We hypothesize that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's staircase" type behavior generic for IC systems. LDA based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.