鉬基磁性異質介面之電流誘發自旋軌道耦合矩及無場翻轉

Current-Induced Spin-Orbit Torque and Field-Free Switching in Mo-Based Magnetic Heterostructures

詹昕頤(Hsin-I Chan)

指導教授 ： 白奇峰

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202000045

摘要

隨著大數據的發展，對於資料的儲存也有更上一層的需求，因此，屬於次世代記憶體中的，磁性隨機存取記憶體的發展，也漸漸受到大家的關注。磁性記憶體主要由兩層鐵磁層及一層鐵磁絕緣層所構成，當兩層鐵磁層的相對方向有變化時，所產生之電阻值亦會產生變化，也可以因此定義邏輯電路的0與1。其中一層鐵磁層的磁化方向為固定的，而另一鐵磁層，可以利用外加電流，產生自旋極化電流（Spin-polarized current）或是淨自旋電流（Net spin current），來進一步控制此層之磁化方向。 產生淨自旋電流的方式，通常是來自於金屬材料本身的自旋霍爾效應，亦即，當電流通入材料時，由於材料本身的自旋軌道耦合矩，在垂直電流的方向上，會產生自旋電流，此自旋電流再進一步影響鐵磁層之磁化方向。然而，在鐵磁層翻轉的過程中，由於自旋軌道矩的特性，需再加入一平行電流之外加磁場，才可以完成磁矩翻轉的過程，而這樣子的特性也在未來的應用上造成阻礙。
在我的研究中，主要是針對鉬（Molybdenum）及鈷鐵硼（CoFeB）的異質接面進行探討，鉬為產生自旋電流的材料，可以利用材料本身之自旋軌道耦合矩來產生自旋電流，而產生之自旋電流將可以進一步影響鈷鐵硼的磁化方向，並達到磁矩翻轉的效果。除了鉬金屬本身的自旋軌道耦合矩的強度測量之外，我們也在此異質接面中，測量到磁矩翻轉的現象，並進一步的，利用產生非平整表面的方式，達到無場磁矩翻轉的現象，而對於我們所產生的非平整表面，也進一步的進行分析。

關鍵字

自旋軌道耦合矩 ； 自旋霍爾效應

並列摘要

As the development of big data is thriving, the demand for a better way of storing information also arises. Magnetoresistive Random Access Memory (MRAM), which is one of the next-generation memory, has grabbed great attention. MRAMs are composed of two ferromagnetic layers with one magnetic-insulating layer sandwiched between them. When the relative magnetization direction of those two ferromagnetic layers is different, the resistance will be different. The magnetization of one of the ferromagnetic layers is fixed and called the reference layer. In contrast, the magnetization in the other ferromagnetic layer can be manipulated by spin-polarized current or net spin current, which can be generated by the current. To generate net spin current, the spin Hall effect of the metal is utilized. When current passes through metal, the spin current will be generated in the direction perpendicular to the current due to the spin-orbit torque of that metal. The generated spin current can further switch the magnetization of the free ferromagnetic layer. However, during the switching process, an external field is required to achieve deterministic switching due to the nature of the spin-orbit torque, which hinders the potential of the application.

In this thesis, the Molybdenum (Mo)/CoFeB heterostructure is studied. The spin current could be generated in the Mo layer and further affect the magnetization in CoFeB and thus enable magnetization switching. The strength of spin-orbit torque is characterized, the field-free magnetization switching is achieved by thin-film deposition at an angle. How such a way of deposition affecting the thin-film structure is also investigated.

並列關鍵字

Spin-orbit torque ； Spin Hall effect

參考文獻

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