有限厚度電極下磁性穿隧接面之自旋轉移力矩

Spin Transfer Torque in Magnetic Tunnel Junctions with Finite Thickness Electrodes

陳政逸(JHENG-YI CHEN)

指導教授 ： 薛文証

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201901983

摘要

本文主要探討磁性穿隧接面中的自旋轉移力矩特性。運用改變材料、結構、磁矩的角度、勢壘層厚度、外加偏壓等方式，來分析對磁性穿隧接面之自旋轉移力矩與穿隧電流造成的影響。自旋極化電流會產生角動量轉移，使其磁矩翻轉，進而產生自旋轉移力矩，造成磁性穿隧接面高低電阻差。本論文使用自由電子模型與轉移矩陣法將其波函數求出，接著用機率流來描述電子行為，進而計算出自旋轉移力矩與穿隧電流。在外加偏壓情況下，平面外的自旋轉移力矩會呈拋物線的反轉對稱性，平面內自旋轉移力矩，會明顯有不對稱性。在改變自由層厚度情況下，發現自旋轉移力矩會隨著自由層厚度而震盪，並且在某個特殊厚度會得到最大值。本文討論共振效應對磁性穿隧接面的影響，共振效應可以有效提升自旋轉移力矩值，使自旋電子元件能夠達到低消耗高輸出的效果。

關鍵字

磁性穿隧接面 ； 自旋轉移力矩 ； 共振效應 ； 自由電子模型 ； 轉移矩陣法

並列摘要

The properties of spin-transfer torque in magnetic tunnel junction is investigated in this thesis. The effects of the spin transfer torque and the current on the magnetic tunnel junction are analyzed by changing material, structures of magnetic moment, angles of magnetic moment, thickness of barrier layer and bias voltage. The spin transfer torque is caused by the spin-polarized current to generate angular momentum, which reverses the magnetic moment, and further causing a high and low resistance difference of the magnetic tunnel junction. In this works, transfer matrix method and free electron model are used to find its wave function, and then used the probability flow to describe electronic behavior, and calculate the spin transfer torque and current on the magnetic tunnel junction. In the case of external bias, the out-of-plane spin transfer torque is parabolic reverse symmetry, and the in-plane spin transfer torque is obviously asymmetrical. In the case of changing the thickness of the free layer, the spin transfer torque oscillates with the thickness of the free layer, and the maximum value is obtained at a certain thickness. The effect of the resonance effect on the magnetic tunneling junction is discussed in this works. The resonance effect can increase the value of the spin transfer torque, and effectively improving the performance of spintronic devices.

並列關鍵字

magnetic tunneling junction ； spin transfer torque ； resonant effect ； free-electron model ； transfer matrix method

參考文獻

[1] W. Zhao, E. Belhaire, C. Chappert, and P. Mazoyer, “Spin transfer torque (STT)-mram--based runtime reconfiguration FPGA circuit”, ACM Trans. Embed. Comput. Syst., 9, 1-16 (2009).

[2] I. Žutić, J. Fabian, and S. D. Sarma, “Spintronics: Fundamentals and applications”, Rev. Mod. Phys., 76, 323 (2004).

[3] S. Wolf, D. Awschalom, R. Buhrman, J. Daughton, S. Von Molnar, M. Roukes, A. Y. Chtchelkanova, and D. Treger, “Spintronics: A spin-based electronics vision for the future”, Science, 294, 1488-1495 (2001).

[4] M. N. Baibich, J. M. Broto, A. Fert, F. N. Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich, and J. Chazelas, “Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices”, Phys. Rev. Lett., 61, 2472 (1988).

[5] G. Binasch, P. Grünberg, F. Saurenbach, and W. Zinn, “Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange”, Phys. Rev. B, 39, 4828 (1989).