Tunable layered-magnetism-assisted magneto-Raman effect in a two-dimensional magnet $\mathrm{CrI_3}$

TL;DR

This study combines experimental Raman spectroscopy and theoretical modeling to uncover a layered-magnetism-assisted phonon scattering mechanism in 2D magnet CrI3, revealing complex magnetic and phononic interactions across layers and magnetic fields.

Contribution

It introduces a novel layered-magnetism-assisted phonon scattering mechanism in 2D CrI3, demonstrating layer-dependent phonon splitting and magnetic field effects on multi-phonon processes.

Findings

Layer-dependent splitting of phonons in multilayer CrI3.

Magnetic field influences phonon behavior due to layered magnetism.

Higher-order phonon scattering also exhibits layered-magnetism effects.

Abstract

We use a combination of polarized Raman spectroscopy experiment and model magnetism-phonon coupling calculations to study the rich magneto-Raman effect in the two-dimensional (2D) magnet $\mathrm{CrI_3}$. We reveal a novel layered-magnetism-assisted phonon scattering mechanism below the magnetic onset temperature, whose Raman excitation breaks time-reversal symmetry, has an antisymmetric Raman tensor, and follows the magnetic phase transitions across critical magnetic fields, on top of the presence of the conventional phonon scattering with symmetric Raman tensors in $N$-layer $\mathrm{CrI_3}$. We resolve in data and by calculations that the 1st-order $A_g$ phonon of monolayer splits into a $N$-fold multiplet in $N$-layer $\mathrm{CrI_3}$ due to the interlayer coupling ($N$>=2) and that the phonons with the multiple show distinct magnetic field dependence because of their different layered-magnetism-phonon coupling. We further find that such a layered-magnetism-phonon coupled Raman scattering mechanism extends beyond 1st-order to higher-order multi-phonon scattering processes. Our results on magneto-Raman effect of the 1st-order phonons in the multiplet and the higher-order multi-phonons in $N$-layer $\mathrm{CrI_3}$ demonstrate the rich and strong behavior of emergent magneto-optical effects in 2D magnets and underlines the unique opportunities of new spin-phonon physics in van der Waals layered magnets.