# Double-Exchange Interaction in Optically Induced Nonequilibrium State: A Conversion from Ferromagnetic to Antiferromagnetic Structure

## TL;DR

This study reveals that intense photoexcitation can invert the double-exchange interaction from ferromagnetic to antiferromagnetic, inducing a transient AFM state in a metallic ferromagnet through nonequilibrium electron dynamics.

## Contribution

It demonstrates that optical excitation can switch the double-exchange interaction from ferromagnetic to antiferromagnetic, a novel control mechanism for magnetic states.

## Key findings

- Photoexcitation induces a transient AFM state from FM.
- The FM-to-AFM conversion time scales with light parameters.
- Hidden AFM interaction arises from nonequilibrium electron-spin coupling.

## Abstract

The double-exchange (DE) interaction, that is, a ferromagnetic (FM) interaction due to a combination of electron motion and the Hund coupling, is a well known source of a wide class of FM orders. Here, we show that the DE interaction in highly photoexcited states is antiferromagnetic (AFM). Transient dynamics of quantum electrons coupled with classical spins are analyzed. An ac field applied to a metallic FM state results in an almost perfect N\'eel state. A time characterizing the FM-to-AFM conversion is scaled by light amplitude and frequency. This hidden AFM interaction is attributable to the electron-spin coupling under nonequilibrium electron distribution.