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• Chinese Optics Letters
• Vol. 20, Issue 11, 111201 (2022)
Junying Ma, Feng Gu, Ying Xu, Jiaming Le, Fanlong Zeng, Yizheng Wu, and Chuanshan Tian*
Author Affiliations
• State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
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Junying Ma, Feng Gu, Ying Xu, Jiaming Le, Fanlong Zeng, Yizheng Wu, Chuanshan Tian. Improving the sensitivity of DC magneto-optical Kerr effect measurement to 10−7$rad/Hz$[J]. Chinese Optics Letters, 2022, 20(11): 111201 Copy Citation Text show less

Abstract

A high-sensitivity DC magneto-optical Kerr effect (MOKE) apparatus is described in this Letter. Via detailed analysis on several dominating noise sources, we have proposed solutions that significantly lower the MOKE noise, and a sensitivity of $1.5×10-7 rad/Hz$ is achieved with long-term stability. The sensitivity of the apparatus is tested by measuring a wedge-shaped Ni thin film on $SiO2$ with Ni thickness varying from 0 to 3 nm. A noise floor of $1.5×10-8 rad$ is demonstrated. The possibility of further improving sensitivity to $10-9 rad$ via applying AC modulation is also discussed.

1. Introduction

Polarization measurement has gained broad applications in many research topics, including magnetic anisotropy[1], spin dynamics[2,3] in magnetic material, birefringence in chiral media[4], and electro-optic sampling technique[5]. In magnetism, one convenient and popular analytical tool is based on the magneto-optical effect, which alters the polarization of the reflected (Kerr effect) and the transmitted light (Faraday effect) through the asymmetric dielectric tensor induced by magnetization[1]. Since its first application to surface magnetism[6], the magneto-optical Kerr effect (MOKE) has been developed as a non-intrusive and versatile probe for remote measurements on static or dynamic properties of spin systems with very high sensitivity, e.g., spin Hall effect[7,8], ultrafast spin dynamics[9], imaging magnetic domain and nanostructure[10,11], as well as magneto-optic information storage[12]. However, because the polarization of light is very sensitive to a large variety of noise sources, it is difficult to achieve a sensitivity of $10−7 rad/Hz$ in MOKE measurement, especially in the DC detection scheme[1,8,1315]. This hampers the application of MOKE in many emerging subjects, such as spin Hall effect[7], time-reversal-symmetry-breaking (TRSB) states in a superconductor[16,17], where a sensitivity of $10−7–10−8 rad$ is urgently needed.

Junying Ma, Feng Gu, Ying Xu, Jiaming Le, Fanlong Zeng, Yizheng Wu, Chuanshan Tian. Improving the sensitivity of DC magneto-optical Kerr effect measurement to 10−7$rad/Hz$[J]. Chinese Optics Letters, 2022, 20(11): 111201