铁磁异质结的远红外脉冲辐射及其光热调控研究  

Pulsed far-infrared radiation of ferromagnetic heterojunction and its photothermal regulation

作　　者：褚欣博 金钻明 吴旭 李婧楠 沈阳 王若愚 季秉煜 李章顺 彭滟[1] Chu Xin-Bo;Jin Zuan-Ming;Wu Xu;Li Jing-Nan;Shen Yang;Wang Ruo-Yu;Ji Bing-Yu;Li Zhang-Shun;Peng Yan(Terahertz Technology Innovation Research Institute,Shanghai Key Lab of Modern Optical System,Engineering Research Center of Optical Instrument and System(Ministry of Education),Terahertz Spectrum and Imaging Cooperative Innovation Center,University of Shanghai for Science and Technology,Shanghai 200093,China)

机构地区：[1]上海理工大学,太赫兹技术创新研究院,上海市现代光学系统重点实验室,光学仪器与系统教育部工程中心,太赫兹光谱与影像技术协同创新中心,上海200093

出　　处：《物理学报》2023年第15期253-260,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:61975110,61988102);高等学校学科创新引智计划(111计划)(批准号:D18014);上海市科技创新行动计划(批准号:22JC1400202);上海市科委国际联合实验室项目(批准号:17590750300);上海市科委重点项目(批准号:YDZX20193100004960);上海市科学技术委员会科技创新行动计划(批准号:21JC1402600);上海市青年科技启明星计划(批准号:18QA1401700);上海市教育委员会和上海市教育发展基金会“晨光计划”(批准号:16CG45);上海高校青年东方学者计划(批准号:QD2015020)资助的课题.

摘　　要：飞秒激光脉冲辐照在Pt/CoFe/Ta铁磁异质结上,导致铁磁层中磁化强度超快淬灭并产生瞬态自旋流.自旋流向重金属层扩散,基于逆自旋霍尔效应在重金属层中转换成瞬态电荷流,产生宽带远红外脉冲辐射.本文通过两方面实验,研究飞秒激光的光热效应对铁磁异质结产生远红外辐射的调控.首先,通过改变外加磁场的大小和方向,研究远红外辐射脉冲振幅-磁场的磁滞回线.与振动样品磁力计测量的磁滞回线相比,远红外辐射脉冲振幅-磁场的磁滞回线表现出更小的矫顽力.增大抽运光的能量密度,发现样品的矫顽力进一步下降.其次,对Pt/CoFe/Ta三层异质结进行正向磁化饱和后施加一个反向的小磁场,实验发现当入射的激光能量密度超过1.43 mJ/cm^(2)时,远红外辐射脉冲信号发生极性的反转.上述两个实验结果不仅阐明飞秒激光脉冲的光热效应,也为基于电子自旋的远红外辐射脉冲的调控提供新方法.Under illumination of a femtosecond laser pulse on the Pt/CoFe/Ta trilayer heterostructure,an impulsive spin current can be generated in the ferromagnetic layer due to the ultrafast demagnetization.The spin current is super-diffusively transported and injected into the neighboring heavy metal layers,and is converted into the transversal charge current due to the spin-orbit coupling,which is named inverse spin Hall effect.The transient charge current on a time scale of sub-picosecond gives rise to the electromagnetic radiation in the far-infrared range to the free space.In this work,we demonstrate two kinds of experiments to investigate the modulation of far-infrared emission by photo-thermal effect,which is due to the thermal energy deposed by light pulses on a short timescales.First,the amplitude of the emitted far-infrared pulse as a function of an applied magnetic field is measured,which shows a far-infrared hysteresis behavior.The coercive field of the sample obtained by farinfrared hysteresis is smaller than that obtained by the M-H hysteresis through vibrating sample magnetometer.In addition,the coercive field decreases with pump laser fluence increasing.Second,the control of spin polarization on an ultrafast timescale in the presence of a small magnetic field applied oppositely to that of the magnetization of the ferromagnetic sample.The amplitude of far-infrared time-domain signal reaches a maximum value at a pump fluence of 1.43 mJ/cm^(2).For the pump fluence larger than 1.43 mJ/cm^(2),the farinfrared pulse experiences a phase reversal.After the reversal,a decrease of the laser pump fluence cannot restore the original phase of the far-infrared pulse.The above two experimental results not only elucidate the photothermal effect of femtosecond laser pulses,but also provide a new method for controlling the far-infrared radiation pulses based on ultrafast spintronics.These results demonstrate that far-infrared emission spectroscopy can be used as an ultrafast optical method to investigate magnetic properties,

关 键 词：光热效应 磁滞回线 远红外脉冲发射光谱 远红外脉冲调控 

分 类 号：TN249[电子电信—物理电子学] O482.523[理学—固体物理]