# Terahertz spin dynamics driven by a field-derivative torque

## TL;DR

This paper numerically investigates how the field-derivative torque influences ultrafast spin dynamics driven by THz laser pulses, revealing its significant impact on spin excitation amplitudes in antiferromagnetic oxides.

## Contribution

It demonstrates the importance of including the field-derivative torque alongside the THz Zeeman field for accurate modeling of ultrafast spin dynamics.

## Key findings

- Field-derivative torque significantly increases spin excitation amplitudes.
- Considering both torques provides a more accurate description of spin dynamics.
- Larger damping constants enhance the effects of the field-derivative torque.

## Abstract

Efficient manipulation of magnetization at ultrashort time scales is of particular interest for future technology. Here, we numerically investigate the influence of the so-called field-derivative torque, which was derived earlier based on relativistic Dirac theory [Mondal et al., Phys. Rev. B 94, 144419 (2016)], on the spin dynamics triggered by ultrashort laser pulses. We find that only considering the THz Zeeman field can underestimate the spin excitation in antiferromagnetic oxide systems as, e.g., NiO and CoO. However, accounting for both, the THz Zeeman torque and the field-derivative torque, the amplitude of the spin excitation increases significantly. Studying the damping dependence of field-derivative torque we observe larger effects for materials having larger damping constants.