具半金屬電極磁性穿隧接面之自旋轉移力矩

Abstract

本文主要研究具半金屬電極之單層勢壘磁性穿隧接面結構(半金屬/絕緣層/鐵磁層)與雙層勢壘磁性穿隧接面結構(半金屬/絕緣層/非磁性層/絕緣層/鐵磁層)中自旋轉移力矩之特性，並與兩端皆為一般鐵磁電極之磁性穿隧接面做比較。透過改變磁矩角度的差異、外加電壓的大小、單層勢壘的絕緣層厚度以及雙層勢壘中間非磁性層厚度，探討不同結構、不同材料，以及其他不同外在條件的情況下，對電子注入磁性穿隧接面結構中之穿隧電流以及自旋轉移力矩，分別有甚麼不同的現象與影響。可以藉由分析不同條件，得到最低效耗、高性能的元件性質。自旋轉移力矩是一種利用自旋流產生能夠將磁矩翻轉的力量。本文使用自由電子模型搭配轉移矩陣法，來描述電子行為，並推導出計算自旋轉移力矩的方法。最後，討論半金屬電極以及雙層勢壘結構的共振效應帶來的效益，可提升自旋轉移力矩之值，有助於增進自旋電子元件之效能。

This thesis focuses on the properties of the spin transfer torque with half-metallic electrodes in single barrier magnetic tunnel junctions (half metal/insulating layer/ferromagnetic layer) and double barrier magnetic tunneling junctions (half metal/insulating layer/non-magnetic layer/ insulating layer/ferromagnetic layer)which is compared to the magnetic tunneling junctions with ferromagnetic electrodes at both ends.By changing the angle difference between two magnetic moments, the magnitude of the applied voltage, the thickness of the insulating layer of the single barrier magnetic tunneling junction, and the thickness of the non-magnetic layer of the double barrier magnetic tunneling junction, the different phenomena and effects of tunneling current and spin transfer torques in electron-injected magnetic tunnel junction under different structures, materials, and other different external conditions are explored. The conditions to get the lowest consumption and high performance properties of the device are analyzed. Spin transfer torque which generated by spin current is the strength that can be used to reverse magnetic moments. In this thesis, free electron model and transfer matrix method are used to describe the electronic behavior and calculate the spin transfer torque. Finally, discuss the benefits bring by the half-metallic electrode and the resonance effect of the double-barrier magnetic tunnel junction which contributes to the enhancement of the performance of spintronic devices.