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  • 學位論文

自旋霍爾效應誘發磁翻轉之模型計算

The Numerical Model of Magnetic Switching by Spin Hall Effect

指導教授 : 陳恭 蔡炎熾
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摘要


本論文探討具有垂直異向性之單層鐵磁結構與雙層鐵磁結構,在通入鐵磁層介面內方向的電流下,自旋霍爾效應(Spin Hall effect,SHE)產生之等效場驅動或影響磁矩翻轉的現象。 我們透過Landau–Lifshitz–Gilbert(LLG)方程式計算磁矩隨時間演進的運動過程,並將計算結果與實驗數據進行比較,主題可分為以下幾類: (1)易軸傾斜的單層結構進行固定水平外加場下的電流掃描模擬: 模擬不同磁性異向能傾斜角度、各方向外加磁場下的電流翻轉曲線,探討不同的電流翻轉方式,同時討論其發生翻轉所需要的條件。從計算的結果發現,電流翻轉的方式可由翻轉的動態過程分為兩類:阻尼進動類(Damping)與反阻尼進動類(Anti-damping) ,利用這兩種不同模式的翻轉特性,可分析出不同方向磁性異向能的電流翻轉的不同。 (2)單層固定電流下的垂直磁場掃瞄模擬: 模擬各電流下的磁滯曲線,經由計算結果可得知電流會幫助垂直外加場的磁翻轉,且電流大到一定程度會使磁矩停留在水平方向。並透過解析方法計算翻轉磁場(Hc)表達式,得知其與電流密度與異向能場的關係,並與實驗比較。 (3)雙層固定電流下的垂直磁場掃瞄模擬: 模擬各電流下的磁滯曲線,由計算結果可得知雙層結構在大電流下如同單層結構會產生水平方向的磁性態,比較不同參數所做出的結果,推測出現水平方向磁性態的耦合能場與異向能場參數比例條件,並比較實驗結果。

並列摘要


In this thesis, we study magnetization switching by spin Hall effect (SHE), which is induced by in-plane injected currents for the single magnetic layer system or the double magnetic layers system with perpendicularly anisotropic. We use the Landau–Lifshitz–Gilbert (LLG) equation to simulate the time evolution of magnetization and compare the result with experimental observations. The obtained results are mainly divided into three parts: (1) Simulations of the magnetic switching by introducing a tilted uniaxial perpendicular magnetic anisotropy ,varying injected currents with a fixed in-plane magnetic field. We discuss how magnetic moment precess with the LLG equation in terms of damping torque and Anti-damping torque for predictions for current-induced magnetic switching. (2) Simulations of varying applied magnetic fields with a fixed injected current for the single magnetic layer system. We simulate the dependence of hysteresis loops on different positive (negative) current densities. We obtain the coercivity (Hc) via analysis and make a comparison between simulations and experimental data. (3) Simulations of varying applied magnetic fields with a fixed injected current for the double magnetic layer systems. By introducing an antiferromagnetic coupling term in the LLG equation,the magnetic state of Y-axis can be found out easier than the single magnetic layer system.The comparison between simulations and experimental data are performed for the present system.

參考文獻


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