Ta(Nb)/CoFeB/MgO異質結構中電流引起之等效場探討

本論文是利用Ta(Nb)/CoFeB/MgO/Ta之磁垂直異向性異質結構樣品，經蝕刻成25μm x 250μm之Hall bar元件進行AHE之異常霍爾電阻量測。實驗主要分為三部分 (1)異常霍爾效應(AHE)量測利用Ta(5)/CoFeB(n=1,1.2,1.4 nm)/MgO(1)/Ta(5)及Nb(5)/CoFeB(1.4)/MgO(1)/Ta(5)之樣品進行異常霍爾電壓(電阻)之量測，並將其矯頑場(Hc)及外加電流密度(jC)進行作圖比較。 (2)平面霍爾效應(PHE)量測實驗手法及步驟與異常霍爾效應之量測皆雷同，相異之處僅為外加場之方向，將外加場從z方向改為x方向，觀察改變電流時R-H loop之變化，並將其H-IC曲線作圖與文獻比較。 (3)電流翻轉實驗利用正負電流掃描，當外加電流到達臨界翻轉電流時，磁矩會翻轉，造成異常霍爾電壓(電阻)正負變號，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；垂直異向性

並列摘要

In conventional magnetic random access memory (MRAM) the method of writing uses the magnetization switching. It was found recently when current goes through a magnetic hetero-structure an induced filed may be used for switching. In this thesis, we fabricated Ta(Nb)/CoFeB/MgO hetero-structures by sputtering and carried the study of the current induced switching effect. The sample is etched into a Hall bar with width of 1 μm and length of 10 μm. The anomalous Hall effect (AHE) is measured by a typical 4 probed method. We first observed the coercivity reduces when the current density increasing. Then we used the magnetic field scanning along the charge current direction to do the planar Hall effect (PHE) measurement, thesign of the Hall resistance has changed when the current induced effective field switched the magnetization. After all the magnetic field scanning measurement we used the current bipolar scanning into the Hall bar without external field and discovered that the Hall resistance was changed. This observation confirms that the current induced effective field indeed switches the magnetization with relatively low current density.