# Nonlinear magnetization dynamics driven by strong terahertz fields

## TL;DR

This study combines experimental and numerical methods to investigate nonlinear magnetization dynamics in a metallic film driven by intense terahertz pulses, revealing complex processes including precession, demagnetization, and relaxation.

## Contribution

It provides a detailed analysis of magnetization behavior under strong terahertz fields and predicts new nonlinear regimes achievable with current terahertz technology.

## Key findings

- Magnetization undergoes coherent precession and ultrafast demagnetization.
- Macrospin simulations accurately reproduce experimental dynamics.
- Potential to access novel nonlinear regimes with existing terahertz sources.

## Abstract

We present a comprehensive experimental and numerical study of magnetization dynamics triggered in a thin metallic film by single-cycle terahertz pulses of $\sim20$ MV/m electric field amplitude and $\sim1$ ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect (MOKE), and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing table-top terahertz sources.