Micro-MOKE with optical interference in the study of 2D Cr2Ge2Te6 nanoflake based magnetic heterostructures

Zongwei Ma,Gaoting Lin,Tong Wu,Yuping Sun,Xuan Luo,Jianhao Chen,Yinan Liu,Feng Jin,Chun Zhou,Wang Zhu,Zhigao Sheng,Yang Yang,Yan Sun

doi:10.1063/1.5126944

Abstract

Due to its high sensitivity and sub-micrometer spatial resolution, the microscopic magneto-optical Kerr effect (micro-MOKE) technique has been widely utilized in the study of two-dimensional (2D) magnetic materials and heterostructures. Here, by taking 2D Cr2Ge2Te6 nanoflakes on a silicon wafer substrate as a model system, we present the effect of optical multilayer interference induced “optical artifacts” on the effective micro-MOKE measurements in such a system. It is found that not only the magnitude but also the sign of the micro-MOKE signal could be modulated by the “optical artifacts” with the variation of either the Cr2Ge2Te6 nanoflakes’ thickness or probe light wavelength. The detailed analysis based on the multilayer interference model reveals that there are two kinds of MOKE signals, sign reversal and magnitude modulation behavior, and the interference effect on the MOKE response can be easily predicted from unpolarized optical images. Our findings provide instructional principles on the promotion of micro-MOKE characterization as well as the optical studies in van der Waals magnets.

Highlights

Two-dimensional (2D) van der Waals magnets, for example Cr2Ge2Te6 (CGT) and CrI3, are drawing tremendous attention due to their remarkable physical properties as well as potential applications in the minimization and optimization of spintronic devices.1–3 With the reduction in their thicknesses down to few or even single atomic layer, the effective probing of the magnetization and its dynamics in those 2D magnets become a big challenge
When the 2D magnetic crystals are exfoliated into nanoflakes and the thickness of such nanoflakes is reduced below the penetration depth of the probe light, the nanoflake itself and the additional layers and interfaces will play non-negligible roles, for example, leading to extrinsic “optical artifacts” by introducing optical interference
It is important to explore and to estimate the extrinsic contributions to the overall MOKE response of a multilayer structure composed of a 2D magnetic layer and nonmagnetic dielectric layers, especially when strict numerical calculations are difficult to implement for lack of relevant parameters

Summary

Introduction

Two-dimensional (2D) van der Waals magnets, for example Cr2Ge2Te6 (CGT) and CrI3, are drawing tremendous attention due to their remarkable physical properties as well as potential applications in the minimization and optimization of spintronic devices.1–3 With the reduction in their thicknesses down to few or even single atomic layer, the effective probing of the magnetization and its dynamics in those 2D magnets become a big challenge. The “optical artifacts” introduced by multilayer optical interference on the effective micro-MOKE signal was studied in 2D CGT based heterostructures.

Results

Conclusion