垂直式MgO/CoFeB/Ta 結構中電流驅動的磁滯翻轉

Current-Induced Magnetization Switching in Perpendicularly Anisotropy MagnetizedMgO/CoFeB/Ta

曾威翰(Tzeng Wei Han)

指導教授 ： 陳恭

國立中正大學/理學院/物理學系/碩士(2014年)

摘要

摘要
近年來電流翻轉效應在垂直式磁性穿隧結應用於MRAM備受矚目，然而電流翻轉機制與材料的關係還未清楚，因此我們製備了三組改變上層Ta厚度的上結構樣品，MgO/CoFeB(1.3 nm)/Ta(1, 1.25, and 5 nm)
並且進行蝕刻成Hall bar元件，進行一連串電性量測：
(a)異常霍爾效應量測：
改變電流密度進行R-H曲線比較，發現翻轉場與形狀隨著電流密度有系統化的改變。
(b)趨近水平磁場異常霍爾效應量測：
利用類似異常霍爾效應的手段，但磁場刻意施加在往垂直方向微小偏離的電流方向，進行改變流密度的R-H曲線量測。
(c)電流掃描量測：
利用正負電流掃描，當外加電流到達臨界電流密度時，會發生磁滯翻轉，造成異常霍爾電壓變化，實驗中須外加一微小與電流平行方向之磁場，使等效場產生z方向分量，造成翻轉。

關鍵字

等效場 ； 自旋霍爾效應 ； 電流驅動翻轉 ； 垂直異向性

並列摘要

The current-induced switching (CIS) in perpendicular magnetic thin layers and tunnel junctions has recently attracted lots of attention due to the possibility to achieve higher density magnetic random access magnetic memory(MRAM). However, the mechanism of the CIS and the materials dependence is still not clear.
In this thesis, we fabricated a series of perpendicular magnetized MgO/CoFeB(1.3 nm)/Ta Hall bar structures with Ta thickness = 1, 1.25, and 5 nm, respectively. We found that the magnetic switching, through the measurement of anomalous Hall voltage, show stronger dependence on the Ta thickness relative to the similar structure with bottom Ta layer. The main effect may be interpreted by a current induced field-like-torque. We will discuss the quantitative critical current density as a function of Ta thickness and also explain why the top Ta layer introduces different effect relative to the bottom Ta layers.

並列關鍵字

Perpendicular Magnetic Anisotropy ； Effective Field ； Spin Hall Effect ； Current-Induced Switching

參考文獻

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