# Nutation spectroscopy of a nanomagnet driven into deeply nonlinear ferromagnetic resonance

## TL;DR

This paper demonstrates a new spectroscopic method to observe deeply nonlinear ferromagnetic resonance in nanomagnets, revealing coherent magnetization nutations at large angles, overcoming traditional spin-wave instability limitations.

## Contribution

It introduces a novel spectroscopic technique and analytical model to control and understand highly nonlinear magnetization dynamics in nanostructures.

## Key findings

- Achieved large-angle, spatially coherent ferromagnetic resonance in nanomagnets.
- Demonstrated resonant slow magnetization nutations driven by a second excitation field.
- Provided a theoretical framework for nonlinear magnetization behavior in nanostructures.

## Abstract

Strongly out-of-equilibrium regimes in magnetic nanostructures exhibit novel properties, linked to the nonlinear nature of magnetization dynamics, which are of great fundamental and practical interest. Here, we demonstrate that field-driven ferromagnetic resonance can occur with substantial spatial coherency at unprecedented large angle of magnetization precessions, which is normally prevented by the onset of spin-wave instabilities and magnetization turbulent dynamics. Our results show that this limitation can be overcome in nanomagnets, where the geometric confinement drastically reduces the density of spin-wave modes. The obtained deeply nonlinear ferromagnetic resonance regime is probed by a new spectroscopic technique based on the application of a second excitation field. This enables to resonantly drive slow coherent magnetization nutations around the large angle periodic trajectory. Our experimental findings are well accounted for by an analytical model derived for systems with uniaxial symmetry. They also provide new means for controlling highly nonlinear magnetization dynamics in nanostructures, which open interesting applicative opportunities in the context of magnetic nanotechnologies.