# Mechanisms of FMR line broadening in CoFeB-LiNbO$_3$ granular films in the vicinity of metal-insulator transition

## TL;DR

This study investigates how ferromagnetic resonance line broadening mechanisms in CoFeB-LiNbO$_3$ nanocomposite films change near the metal-insulator transition, highlighting the roles of inhomogeneity and interparticle exchange.

## Contribution

It reveals the transition in FMR linewidth mechanisms across the metal-insulator transition, emphasizing the importance of interparticle exchange in the tunneling regime.

## Key findings

- FMR linewidth is dominated by inhomogeneous anisotropy distribution below MIT.
- Above MIT, two-magnon relaxation significantly contributes to linewidth.
- Interparticle exchange plays a critical role in the tunneling regime.

## Abstract

Metal-insulator (CoFeB)$_x$(LiNbO$_3$)$_{100-x}$ nanocomposite films with different content of the ferromagnetic (FM) phase $x$ are investigated by ferromagnetic resonance (FMR) technique. A strong change of the FMR line shape is observed in the vicinity of metal-insulator transition (MIT) of the film, where the hopping-type conductivity $\sigma$ modifies to the regime of a strong intergranular tunnelling, characterized by a logarithmic dependence $\sigma(T)$ at high temperatures. It is shown that below MIT, the FMR linewidth is mainly determined by the inhomogeneous distribution of the local anisotropy axes in the film plane. Above MIT, the contribution of this inhomogeneity to the line broadening decreases. At the same time, two-magnon magnetic relaxation processes begin to play a significant role in the formation of the linewidth. The observed behaviour indicates the critical role of interparticle exchange in the tunnelling regime above MIT of the nanocomposite.