NMR study of the high-field magnetic phase of LiCuVO$_4$

TL;DR

This study uses NMR to investigate the high-field magnetic phase of LiCuVO$_4$, revealing a spin-modulated structure with inter-chain ferromagnetic interactions and evidence of short-range order at elevated temperatures.

Contribution

First NMR analysis of the high-field spin-modulated phase in LiCuVO$_4$, showing inter-chain ferromagnetic coupling and temperature-dependent magnetic ordering.

Findings

Spin-modulated magnetic structure forms with ferromagnetic inter-chain interactions.

Mutual orientation between spins of neighboring planes appears random.

Short-range magnetic order exists at temperatures above the Néel temperature.

Abstract

We report on NMR studies of the quasi--1D antiferromagnetic $S=1/2$ chain cuprate LiCuVO$_4$, focusing on the high--field spin--modulated phase observed recently in applied magnetic fields $H > H_{\rm c2}$ ($\mu_0H_{\rm c2} \approx 7.5$ T). The NMR spectra of $^7$Li and $^{51}$V around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin--modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the {\bf ab}--plane at low temperatures 0.6 K $ < T < T_{\rm N}$. The best fit provides evidence that the mutual orientation between spins of neighboring {\bf ab}--planes is random. For elevated temperatures $T_{\rm N} < T \lesssim 15$ K, short--range magnetic order occurs at least on the characteristic time scale of the NMR experiment.