# 51V-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8

## TL;DR

This study uses $^{51}$V-NMR to explore static and dynamic magnetic properties of K$_2$V$_3$O$_8$, revealing complex spin behaviors, possible incommensurate structures, and strong spin fluctuations near the magnetic transition.

## Contribution

First detailed $^{51}$V-NMR investigation of K$_2$V$_3$O$_8$ elucidating structural transitions and complex magnetic orderings in this quasi-two-dimensional antiferromagnet.

## Key findings

- NMR spectra consistent with $P4bm$ symmetry above $T_S$
- Spectral splitting and broadening below $T_S$ due to superstructure formation
- Enhanced $1/T_1$ indicating strong gapless spin fluctuations

## Abstract

Static and dynamic properties of the quasi-two-dimensional antiferromagnet K$_2$V$_3$O$_8$ have been investigated by $^{51}$V-NMR experiments on nonmagnetic V$^{5+}$ sites. Above the structural transition temperature $T_{\rm{S}}$ = 115 K, NMR spectra are fully compatible with the $P4bm$ space group symmetry. The formation of superstructure below $T_{\rm{S}}$ causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along $c$-axis below the magnetic transition temperature $T_{\rm{N}} \sim 4$ K is qualitatively consistent with a simple N\'{e}el order and a spin flop transition. However, broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate $1/T_1$ below $T_{\rm{N}}$ shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V$^{5+}$ and magnetic V$^{4+}$ sites. The results indicate strong gapless spin fluctuations, which could arise from incommesurate orders or complex spin textures.