# Valley Spin–Polarization of MoS2 Monolayer Induced by Ferromagnetic Order in an Antiferromagnet

## TL;DR

This paper shows how antiferromagnetic nickel oxide can induce valley spin-polarization in MoS2 monolayers through a magnetic proximity effect.

## Contribution

The study reveals that uncompensated spins in antiferromagnets can generate ferromagnetic order to control valley spin-polarization in TMDs.

## Key findings

- Uncompensated spins in NiO induce valley spin-polarization in MoS2 via magnetic proximity effect.
- Spin-polarized trions are responsible for valley magnetism in MoS2.
- The depolarization temperature is around 100 K, higher than previously reported.

## Abstract

Transition metal dichalcogenide (TMD) monolayers exhibit unique valleytronics properties due to the dependency of the coupled valley and spin state at the hexagonal corner of the first Brillouin zone. Precisely controlling valley spin-polarization via manipulating the electron population enables its application in valley-based memory or quantum technologies. This study uncovered the uncompensated spins of the antiferromagnetic nickel oxide (NiO) serving as the ferromagnetic (FM) order to induce valley spin-polarization in molybdenum disulfide (MoS2) monolayers via the magnetic proximity effect (MPE). Spin-resolved photoluminescence spectroscopy (SR-PL) was employed to observe MoS2, where the spin-polarized trions appear to be responsible for the MPE, leading to a valley magnetism. Results indicate that local FM order from the uncompensated surface of NiO could successfully induce significant valley spin-polarization in MoS2 with the depolarization temperature approximately at 100 K, which is relatively high compared to the related literature. This study reveals new perspectives in that the precise control over the surface orientation of AFMs serves as a crystallographic switch to activate the MPE and the magnetic sustainability of the trion state is responsible for the observed valley spin-polarization with the increasing temperature, which promotes the potential of AFM materials in the field of exchange-coupled Van der Waals heterostructures.