Layer Dependence of Stacking Order in Nonencapsulated Few-layer CrI3

TL;DR

This study investigates the stacking order and interlayer coupling in non-encapsulated few-layer CrI3 at low temperature, revealing rhombohedral stacking and temperature-dependent spin-phonon interactions using Raman spectroscopy.

Contribution

It provides direct experimental evidence of rhombohedral stacking in non-encapsulated CrI3 and explores temperature-dependent spin-phonon coupling effects.

Findings

Rhombohedral stacking confirmed in 2-5 layer and bulk CrI3.

Opposite helicity dependence of Raman modes validates stacking.

Anomalous behavior due to spin-phonon coupling below 60 K.

Abstract

Long-range magnetic orders in atomically thin ferromagnetic CrI3 give rise to new fascinating physics and application perspectives. The physical properties of two-dimensional (2D) ferromagnetism CrI3 are significantly influenced by interlayer spacing and stacking order, which are sensitive to the hydrostatic pressure and external environments. However, there remains debate on the stacking order at low temperature. Here, we study the interlayer coupling and stacking order of non-encapsulated 2-5 layer and bulk CrI3 at 10 K by Raman spectroscopy; demonstrate a rhombohedral stacking in both antiferromagnetic and ferromagnetic CrI3. The opposite helicity dependence of Ag and Eg modes arising from phonon symmetry further validate the rhombohedral stacking. An anomalous temperature-dependent behavior is observed due to spin-phonon coupling below 60 K. Our work provides insights into the interlayer coupling and stacking orders of 2D ferromagnetic materials.