物理学报2024，Vol.73Issue(16)：190-198,9.DOI:10.7498/aps.73.20240703
硅基自旋光电子学太赫兹辐射源特性
Terahertz emission characterization of silicon based ferromagnetic heterostructures
摘要
Abstract
Terahertz spectroscopy and imaging have many applications,so the generation of broadband terahertz radiation is very important,but now it faces some challenges.Opto-spintronic terahertz emitters,composed of nanometer-thin magnetic multilayer,can produce high-quality broad-band terahertz pulses.Integration of opto-spintronic terahertz emitters onto the silicon wafers is the first step towards their usage in modern photonic devices.In this work,Ta/CoFeB/Ir heterostructures are deposited on thermally oxidized silicon wafers by dc magnetron sputtering.Under the illumination of a femtosecond laser pulse on the Ta/CoFeB/Ir trilayer heterostructure grown on silicon substrate,a spin current can be generated in the ferromagnetic layer due to the ultrafast demagnetization.The spin current is transported and injected into the neighboring non-magnetic metal layers of Ta and Ir.Consequently,the spin current can be converted into the charge current due to the strong spin-orbit coupling.The sub-picosecond transient charge current gives rise to the terahertz radiation that enters into the free space.The terahertz electric field is fully inverted when the magnetization is reversed,which indicates a strong connection between THz radiation and spin order of the heterostructure.The THz radiation from Ta/CoFeB/Ir heterostructure covers the 0.1-2.5 THz frequency range with a maximum value of about 0.64 THz.We also investigate the dependence of THz peak-to-peak value on the pump fluence.The THz emission is found to be saturated at a pump fluence of～0.73 mJ/cm2.Our results demonstrate the existence of the strong spin-orbit coupling in the heavy metal Ir.Furthermore,we optimize the THz emission from the Ta/CoFeB/Ir heterostructure by changing the thickness of Ir layer.According to the thickness dependence of THz emission from the heterostructure,the propagation length of the spin current at THz frequencies is extracted to be about(0.59±0.12)nm,which is shorter than the GHz experimental measurement(～1.34 nm).Our experimental observation is consistent with that in the antiferromagnet IrMn layer,which may be attributed to different transport regimes.Theoretically,the optimized thickness values for CoFeB and Ir layers are 2.4 nm and 1.1 nm,respectively.关键词
宽带太赫兹辐射/铁磁异质结/逆自旋霍尔效应/自旋扩散长度Key words
broadband terahertz radiation/ferromagnetic heterostructure/inverse spin hall effect/spin diffusion length引用本文复制引用
程宏阳,马倩茹,徐浩然,张慧萍,金钻明,何为,彭滟..硅基自旋光电子学太赫兹辐射源特性[J].物理学报,2024,73(16):190-198,9.基金项目
国家重点研发计划(批准号:2023YFF0719200,2022YFA1404004)、国家自然科学基金(批准号:61988102,62322115)、高等学校学科创新引智计划(111计划)(批准号:D18014)和上海市科技创新行动计划(批准号:22JC1400200,21S31907400)资助的课题. Project supported by the National Key Research and Development Program of China(Grant Nos.2023YFF0719200,2022YFA1404004),the National Natural Science Foundation of China(Grant Nos.61988102,62322115),the 111Project(Grant No.D18014),and the Science and Technology Commission of Shanghai Municipality,China(Grant Nos.22JC1400200,21S31907400). （批准号:2023YFF0719200,2022YFA1404004）
