Magneto-Optical Study of Chiral Magnetic Modes in NiI$_{2}$: Direct Evidence for Kitaev Interactions

TL;DR

This study provides direct experimental evidence that Kitaev interactions significantly influence the magnetic excitations in NiI$_{2}$, a van der Waals multiferroic, challenging previous helical spin models and advancing understanding of quantum magnetic phenomena.

Contribution

The paper presents the first direct experimental evidence that Kitaev interactions govern magnetic excitations in NiI$_{2}$, a van der Waals material, using magneto-optical measurements.

Findings

Kitaev-based spin model better explains NiI$_{2}$'s magnetic spectrum.

Magneto-transmission and circular dichroism measurements support Kitaev interactions.

Evidence challenges previous helical spin framework for NiI$_{2}$.

Abstract

Bond-dependent magnetic interactions, particularly those described by the Kitaev model, have emerged as a key pathway toward realizing unconventional magnetic states such as quantum spin liquids and topologically nontrivial excitations, including skyrmions. These interactions frustrate conventional magnetic order and give rise to rich collective behavior that continues to challenge both theory and experiment. While Kitaev physics has been extensively explored in the context of honeycomb magnets, direct evidence for its role in real materials remains scarce. Magnetic van der Waals (vdW) materials have emerged as a versatile platform for exploring low-dimensional electrical, magnetic, and correlated electronic phenomena, and provide a fertile ground for potential applications ranging from spintronics to multiferroic devices and quantum information technologies. Here, we demonstrate, through magneto-transmission, Faraday angle rotation, and magnetic circular dichroism measurements, that the magnetic excitation spectrum of NiI$_2$, a van der Waals multiferroic material, is more accurately captured by a Kitaev-based spin model than by the previously invoked helical spin framework.