外加偏壓下磁性穿隧接面之自旋轉移力矩

Abstract

本文主旨為研究於磁性穿隧接面中的自旋轉移力矩特性，自旋轉移力矩是一種使用自旋極化電流趨動鐵磁性金屬中磁化的自旋電子學概念，受到力矩的磁矩將會進行轉動甚至是翻轉，本研究探討自旋轉移力矩的性質，首先在理論上使用自由電子模型建構出於金屬內傳輸的自旋流的基本性質，並且使用了轉移矩陣法求出磁性穿隧接面內的自旋流，最後使用自旋角動量守恆得到兩種分量的自旋轉移力矩，分別為平面內力矩與平面外力矩。透過對磁性穿隧接面與外加偏壓之參數分析，發現了元件的厚度、位能、自旋分裂能與外加偏壓等變化而影響到穿隧磁阻以及自旋轉移力矩的大小，並且即使在對稱結構中力矩對電壓也會呈現非對稱關係。自旋轉移力矩現象最主要的用途在使用電流而不是磁場調控磁阻大小，本研究提供製作元件的參考，有助於提升磁性穿隧接面中關於自旋轉移力矩的性能。

In this thesis, the properties of spin-transfer torque in magnetic tunnel junction are studied. In the beginning, free electron model is used to construct the basic properties of the transfer of spin current. The spin current in magnetic tunnel junction is calculated using transfer matrix method. Spin angular momentum conservation is used to obtain the spin transfer torques, which have two components, in-plane torque and out-of-plane torque. The numerical results show that the bias-induced spin-transfer torque is a function of angle between magnetic moments, barrier height, thickness and spin splitting energy. It is find that the bias voltage dependence of the spin torque is not symmetric, even for symmetric magnetic tunnel junctions.