Enhanced Magnetization by Defect-Assisted Exciton Recombination in Atomically Thin CrCl$_3$

TL;DR

This study demonstrates that defect-assisted exciton recombination can significantly enhance the in-plane magnetization of atomically thin CrCl$_3$, revealing a new pathway for tuning magnetic properties via optical and defect engineering.

Contribution

It introduces a novel mechanism where defect-assisted exciton recombination enhances magnetization in 2D magnetic materials, supported by experimental and theoretical analysis.

Findings

Exciton recombination boosts in-plane magnetization in CrCl$_3$

Nonradiative exciton recombination increases in atomically thin layers

Defect-assisted Auger recombination activates electron transfer from surface impurities

Abstract

Two dimensional (2D) semiconductors present unique opportunities to intertwine optical and magnetic functionalities and to tune these performances through defects and dopants. Here, we integrate exciton pumping into a quantum sensing protocol on nitrogen-vacancy centers in diamond to image the optically-induced transient stray fields in few-layer, antiferromagnetic CrCl$_3$. We discover that exciton recombination enhances the in-plane magnetization of the CrCl$_3$ layers, with a predominant effect in the surface monolayers. Concomitantly, time-resolved photoluminescence measurements reveal that nonradiative exciton recombination intensifies in atomically thin CrCl$_3$ with tightly localized, nearly dipole-forbidden excitons and amplified surface-to-volume ratio. Supported by experiments under controlled surface exposure and density functional theory calculations, we interpret the magnetically enhanced state to result from a defect-assisted Auger recombination that optically activates electron transfer between water vapor related surface impurities and the spin-polarized conduction band. Our work validates defect engineering as a route to enhance intrinsic magnetism in single magnetic layers and opens a novel experimental platform for studying optically-induced, transient magnetism in condensed matter systems.