# Probing magnon dynamics and interactions in a ferromagnetic spin-1 chain

## TL;DR

This study investigates magnon dynamics in a nearly ideal 1D spin-1 ferromagnetic chain, revealing temperature-dependent renormalization of spin excitations due to magnon-magnon interactions, unique to spin-1 systems.

## Contribution

The paper provides the first detailed experimental and theoretical analysis of magnon interactions in a spin-1 ferromagnetic chain, highlighting phenomena absent in spin-1/2 systems.

## Key findings

- Observation of a magnon-like excitation at low temperatures
- Temperature-dependent renormalization of spin-excitation energy
- Magnon-magnon interactions explained by theoretical models

## Abstract

NiNb$_{2}$O$_{6}$ is an almost ideal realization of a 1D spin-1 ferromagnetic Heisenberg chain compound with weak unidirectional anisotropy. Using time-domain THz spectroscopy, we measure the low-energy electrodynamic response of NiNb$_{2}$O$_{6}$ as a function of temperature and external magnetic field. At low temperatures, we find a magnon-like spin-excitation, which corresponds to the lowest energy excitation at $q\sim0$. At higher temperatures, we unexpectedly observe a temperature-dependent renormalization of the spin-excitation energy, which has a strong dependence on field direction. Using theoretical arguments, exact diagonalizations and finite temperature dynamical Lanczos calculations, we construct a picture of magnon-magnon interactions that naturally explains the observed renormalization. This unique scenario is a consequence of the spin-1 nature and has no analog in the more widely studied spin-1/2 systems.