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铁磁介质与稀磁半导体的自旋相关光电特性研究
【作者】 柏利慧；
【作者基本信息】 复旦大学 ， 光学， 2008， 博士
【摘要】 本文重点讨论介质中电子自旋性质及其与电荷输运的关系,这是自旋电子学研究的核心问题。介质在外磁场中,电子能级发生塞曼分裂,自旋极化载流子发生跃迁和转移。我们采用电学和光学方法分别研究了铁磁和稀磁半导体介质中的自旋极化的载流子的性质。本文的主要工作如下:我们在实验上研究了磁动力学过程与电荷输运的关系,观察到了发生在铁磁体介质中的光电压效应。它是介质的体效应,其物理根源是微波驱动的磁矩进动与微波电流的耦合。我们由此发展了自旋整流效应理论,很好的解释了实验上观察到的铁磁介质中的光电压、光电流、光电阻等现象。自旋整流效应的发现为利用电学方法测量铁磁介质中的磁动力学过程(如铁磁共振和自旋波)提供了全新的思路。基于该原理,我们深入讨论了各种尺寸的铁磁介质在不同外磁场位形下的磁动力学过程。结合朗道栗弗席茨吉尔伯特方程和麦克斯韦方程边界条件,我们系统阐述各类自旋波模式的动力学理论,解释了在特殊位形下不均匀静磁场区域中的局域模式及其与表面静磁模之间的发展转化过程。根据自旋整流效应,我们设计并制备出一种全新的探测射频电磁波磁矢量的探测器,较已有的回路线圈磁场探测器,新的探测器能够探测微波磁场矢量,并且实现在亚波长尺寸内对微波的探测。本文从理论和实验角度分别验证这一探测器的工作原理和品质。本文的第二部分内容主要研究稀磁半导体中自旋极化电子的激发、转移和复合等运动行为,它是自旋电子学的另一个重要的研究方向。本文采用磁光光谱方法,研究稀磁性半导体中自旋极化的载流子在外磁场的作用下的行为,实验观察塞曼效应导致的自旋极化载流子的能级分裂,及自旋极化载流子在能级和空间的转移行为。从而为半导体工艺下的自旋电子学新型器件的设计提供了很好的基础。
【Abstract】 In this dissertation, the properties of spin-polarized carriers in ferromagnetic materials and diluted magnetic semiconductors (DMSs), which are of great importance for spintronics applications, are studied.In the first part of this dissertation, we summarized and developed a spin rectification effect (SRE) theory. Basing on the SRE theory, we studied the magnetic dynamics of a permalloy (Py) strip. The experimental observation of a time-independent photo-voltage resulting from the coupling between magnetization procession and microwave current was well interpreted.Based on the SRE and the above study, a new technique is developed to electrically detect the spin dynamics in the ferromagnetic material. The spin dynamics is probed in different configuration. With the Laudan-lifshitz-Gilbert equation and the boundary condition for the Maxwell Equation, we discussed the physical original of various spin wave modes, such as ferromagnetic resonance, perpendicular standing spin wave, magneto-static mode and localized mode.By measuring and analyzing the angular dependence of the photovoltage induced by the spin rectification effect, a new approach is demonstrated for making novel microwave detectors capable of detecting the rf magnetic field vector at sub-wavelength scale.In the second part of this dissertation, we studied the magneto-optical properties of ZnMnTe/ZnMgTe hetero structure by using photoluminescence (PL) spectroscopy at low temperature. The circularly-polarized PL measurements in an increasing magnetic field were performed. Detailed characteristics of the level crossing behavior for the spin polarized excitonic states due to the giant Zeeman splitting were observed. These features are conformed by the behavior of the PL intensity in magnetic field, and agree well with the theoretical expectation basing on the sp-d exchange interaction.