Ultrafast enhancement of ferromagnetic spin exchange induced by ligand-to-metal charge transfer

TL;DR

This paper demonstrates that ultrafast laser excitation of ligand-to-metal charge transfer can significantly enhance ferromagnetic spin exchange in a superexchange magnet, enabling rapid control of magnetic states.

Contribution

It introduces a novel mechanism for enhancing spin exchange via ligand-to-metal charge transfer, demonstrated in CrSiTe3 using phase-resolved coherent phonon spectroscopy.

Findings

Sub-picosecond enhancement of ferromagnetic exchange observed.

Mechanism involves real charge transfer from ligand to magnetic site.

Applicable in both magnetic and paramagnetic phases.

Abstract

Directly modifying spin exchange energies in a magnetic material with light can enable ultrafast control of its magnetic states. Current approaches rely on tuning charge hopping amplitudes that mediate exchange by optically exciting either virtual or real charge-transfer transitions (CT) between magnetic sites. Here we show that when exchange is mediated by a non-magnetic ligand, it can be substantially enhanced by optically exciting a real CT transition from the ligand to magnetic site, introducing lower order virtual hopping contributions. We demonstrate sub-picosecond enhancement in a superexchange dominated ferromagnet CrSiTe3 through this mechanism using phase-resolved coherent phonon spectroscopy. This technique can also be applied in the paramagnetic phase to disentangle light induced exchange modification from other ultrafast effects that alter the magnetization. This protocol can potentially be broadly applied to engineer thermally inaccessible spin Hamiltonians in superexchange dominated magnets.