# NMR Determination of an Incommensurate Helical Antiferromagnetic Structure in EuCo2As2

## TL;DR

This study uses NMR techniques to identify and characterize an incommensurate helical antiferromagnetic structure in EuCo2As2, providing a model-independent determination of its magnetic propagation vector.

## Contribution

The paper demonstrates that NMR can uniquely determine the incommensurate helical AFM structure and its propagation vector without relying on model-dependent assumptions.

## Key findings

- Identification of incommensurate helical AFM structure in EuCo2As2
- Model-independent determination of the AFM propagation vector
- NMR as a tool for spin structure analysis in incommensurate AFMs

## Abstract

We report $^{153}$Eu, $^{75}$As and $^{59}$Co nuclear magnetic resonance (NMR) results on EuCo$_2$As$_2$ single crystal. Observations of $^{153}$Eu and $^{75}$As NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature $T_{\rm N}$ = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo$_2$As$_2$. Furthermore, based on $^{59}$Co NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector ${\bf k}$ = (0, 0, 0.73 $\pm$ 0.07)2$\pi$/$c$ where $c$ is the $c$ lattice parameter. Thus the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.