# Deconstruction of the Anisotropic Magnetic Interactions from Spin‐Entangled Optical Excitations in van der Waals Antiferromagnets

## TL;DR

This paper studies how light interacts with magnetic properties in van der Waals antiferromagnets to reveal key magnetic parameters.

## Contribution

A high-fidelity ab initio method is used to deconstruct spin-entangled optical excitations and determine magnetic coupling constants.

## Key findings

- Spin-entangled optical transitions originate from on-site spin-flip transitions at magnetic atoms.
- Ab initio calculations reveal atom- and orbital-specific contributions to sub-bandgap electronic transitions.
- Magnetic field experiments help deduce effective exchange coupling and anisotropy constants.

## Abstract

Magneto‐optical excitations in antiferromagnetic d systems can originate from a multiplicity of light‐spin and spin‐spin interactions, as the light and spin degrees of freedom can be entangled. This is exemplified in van der Waals systems with attendant strong anisotropy between in‐plane and out‐of‐plane directions, such as MnPS3 and NiPS3 films studied here. The rich interplay between the magnetic ordering and sub‐bandgap optical transitions poses a challenge to resolve the mechanisms driving spin‐entangled optical transitions, as well as the single‐particle bandgap itself. Here, a high‐fidelity ab initio theory is applied to find a realistic estimation of the bandgap by elucidating the atom‐ and orbital‐resolved contributions to the fundamental sub‐bands. It is further demonstrated that the spin‐entangled excitations, observable as photoluminescence and absorption resonances, originate from an on‐site spin‐flip transition confined to a magnetic atom (Mn or Ni). The evolution of the spin‐flip transition in a magnetic field is used to deduce the effective exchange coupling and anisotropy constants.

A self‐consistent ab initio many‐body perturbation theory combined with locally exact dynamical mean field theory is employed to compute the sub‐bandgap electronic transitions in van der Waals antiferromagnets. The rich interplay between the magnetic ordering and spin‐entangled optical transitions, manifested as photoluminescence and absorption resonances, enables the determination of critical parameters that stabilize magnetic order in these systems.