# Ultrafast optical excitation of coherent magnons in antiferromagnetic NiO

## TL;DR

This study combines experimental and theoretical approaches to uncover the mechanisms behind ultrafast optical magnon excitation in NiO, revealing the dominant role of the inverse Cotton-Mouton effect and providing insights into spin dynamics.

## Contribution

The paper presents a symmetry-based theoretical model that explains experimental observations of ultrafast magnon excitation in NiO, highlighting the efficiency difference between inverse Cotton-Mouton and inverse Faraday effects.

## Key findings

- Inverse Cotton-Mouton effect is three orders of magnitude more efficient than inverse Faraday effect in NiO.
- Experiment and theory show striking agreement in magnon excitation mechanisms.
- Spin domain distribution can be inferred from optical measurements.

## Abstract

In experiment and theory, we resolve the mechanism of ultrafast optical magnon excitation in antiferromagnetic NiO. We employ time-resolved optical two-color pump-probe measurements to study the coherent non-thermal spin dynamics. Optical pumping and probing with linearly and circularly polarized light along the optic axis of the NiO crystal scrutinizes the mechanism behind the ultrafast optical magnon excitation. A phenomenological symmetry-based theory links these experimental results to expressions for the optically induced magnetization via the inverse Faraday effect and the inverse Cotton-Mouton effect. We obtain striking agreement between experiment and theory that, furthermore, allows us to extract information about the spin domain distribution. We also find that in NiO the energy transfer into the magnon mode via the inverse Cotton-Mouton effect is about three orders of magnitude more efficient than via the inverse Faraday effect.