垂直式人工反鐵磁多層膜結構 MgO/CoFeB/Ru/CoFeB/MgO之自旋霍爾效應

Spin Hall Effect of perpendicular magnetic synthetic antiferromagnetic structure MgO/CoFeB/Ru/CoFeB/MgO

陳奕成(I-CHENG CHEN)

指導教授 ： 陳恭

國立中正大學/理學院/物理學系/碩士(2015年)

摘要

本論文拓展電流誘發翻轉的研究，利用濺鍍方式製作反鐵磁耦合結構MgO/CoFeB/Ru/CoFeB/MgO的薄膜，此結構由於MgO/CoFeB界面效應，具備垂直磁異向性(PMA)特性。詳細的膜厚為Sub/ Ta(10)/ MgO(1)/ CoFeB(1.2)/ Ru(2.2)/ CoFeB(1.2) / MgO(1) / Ta(3) 單位是nm。我們將其蝕刻成10μm x 100μm之Hall bar元件。量測的方式是將電流注入Hall bar元件中，電流方向為縱向方向，施加外加磁場的方向是沿著電流方向(或與易磁化軸夾θ角度)進行異常霍爾電性量測，實驗主要分為兩部分：
1.異常霍爾效應(AHE)量測
改變電流密度的方向及大小進行磁場掃描，有系統地整理霍爾電阻的曲線，並根據這些曲線的特徵以及磁性態畫出H-J相圖。這些相圖的特點因為正負電流產生之等效場方向不同，導致圖形左右對稱性破壞。
2.電流驅動磁矩翻轉
在此實驗中需加入固定微小的磁場，進行電流掃描，當電流達到臨界電流時，磁矩發生翻轉。根據這些曲線的臨界電流大小畫出J-H相圖。此相圖呈現出以下特點：電流密度為正時， 臨界電流約為36 MA/cm2，當外加磁場增加，臨界電流值為負並乎呈線性從-20 MA/cm2遞減至-9 MA/cm2。此現象與材料中的耦合能大小有關，在文中有詳細的討論。另外，此結構在不施加外加磁場的情況下亦能引發磁矩翻轉之現象，表示系統面內的對稱性破缺的特性，同時此零場翻轉的現象有具有未來製作元件的潛力。

關鍵字

人工反鐵磁結構 ； 鈷鐵硼 ； 自旋軌道力矩 ； 自旋霍爾效應 ； 垂直磁異向性

並列摘要

Abstract
We fabricated a coupled ferromagnetic structure of MgO/CoFeB/Ru/ CoFeB/MgO and studied current induced magnetic switching in this system. The exchange coupling between CoFeB layers is through the Ru spacer and the MgO layers on the side provide the interfacial perpendicular magnetic anisotropy (PMA). The thickness of each layer is given as: Sub/Ta(10)/MgO(1)/CoFeB(1.2)/Ru(2.2)/CoFeB(1.2)/MgO(1)/Ta(3) (all units: nm). The film is then etched into a Hall bar with width of 10 μm and length of 100 μm.
The Hall resistance is measured by injecting a current alon ghte Hall bar longitudinal direction. During the measurement, an external magnetic field may apply at different direction. The results are divided into two parts:
(1) The measurement of anomalous Hall effect (AHE)
Varying the direction and magnitude of the current density and systematically measured Hall resistance curve. Based on the characteristic of the Hall loops, the H-J phase diagram are mapped out. The phase diagram typically shows asymmetry between the positive and negative. In addition, multiple switching is observed in some regions.
(2) Current driven magnetic reversal
The Hall resistance is measured as a function of current density under a small in-plane magnetic field. During the measurements, when the current reaches critical values, the Hall resistance shows switching behavior. J-H diagrams are the mapped out. The critical current density is ~ 36 MA/cm2 and stays constant as the current is positive. However, the critical current density decreases from -20 MA/cm2 to -9 MA/cm2 as the current is negative.
Moreover, we found that the current induced magnetic switching occurs in these coupled double ferromagnetic layered structure. This zero-field switching indicates that the up-down symmetry is intrinsically broken and this feature may have application potential.

Keywords：Spin Hall Effect、spin-orbital torque、Synthetic antiferromagnetic structure、CoFeB、Perpendicular magnetic anisotropy

並列關鍵字

Synthetic antiferromagnetic structure ； CoFeB ； spin-orbital torque ； Spin Hall Effect ； Perpendicular magnetic anisotropy

參考文獻

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