鈷/鉑多層膜及鋱(鐵)鈷薄膜系統的磁交互耦合作用

Magnetic Exchange Coupling between Co/Pt Multilayers and Tb(Fe)Co Films

林夢嫺(Meng-Shian Lin)

指導教授 ： 賴志煌

國立清華大學/工學院/材料科學工程學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00420

摘要

本論文著重於鈷/鉑多層膜及鋱(鐵)鈷薄膜系統的磁交互耦合作用之研究。
首先，鍍製了[Co/Pt]n/CoFe/Cu/CoFe/TbCo薄膜之垂直式自旋閥結構。使用水平流向電流的磁阻電性量測此種垂直式巨磁阻結構，得到高達4.8 %的磁阻值。然而，這種結構仍然存在著造成記錄動作不穩定的層間耦合作用力，且此作用力會隨著鈷鐵/鋱鈷薄膜的淨磁矩增加而增加。因而，研究並鍍製出具有高矯頑場(7 kOe)和磁矩互相抵銷而幾乎沒有淨磁矩存在的垂直式釘札薄膜結構，使得自由層和被釘札層之間的層間耦合作用可以大大地被抑制。故此種垂直式釘札結構可能適合高記錄密度垂直式磁性記憶體的未來應用。
第二部分研究了[Co/Pt]n/Co/Ru/Co/TbCo薄膜結構的特殊垂直式層間耦合作用力，即此層間耦合作用力的強度會隨著釕間隔層厚度變化而有一振盪的行為產生。當釕間隔層厚度在0.5-1 奈米時，可以觀察到一個強的反鐵磁耦合作用(大約0.38 erg/cm2)。另外，儘管釕厚度維持一定，但是鈷/鉑多層膜的次要磁滯曲線偏移方向仍可以被自由地控制，這是由於鋱鈷的磁矩可以隨著組成和量測溫度的調變而變化。此外，利用X光磁圓偏振能譜來量測鋱鈷內的鋱和鈷之磁矩傾斜角。這個有趣的實驗結果發現，垂直式層間耦合作用隨著釕厚度變化之振盪行為發生的同時，鋱鈷內的鋱和鈷之磁矩傾斜角會有相反方向開合排列的趨勢，代表著此層間耦合作用力作用於鋱鈷內的鋱和鈷之磁矩的確是有著不同的特性。而且，這個實驗結果可以和理論計算結果完美地互相匹配。此種獨特的磁矩行為亦可能可以作為自旋電子元件的未來應用。
最後，研究具有垂直磁異向性的[Co/Pt]n/Co/TbFeCo薄膜結構之界面交互耦合作用力，並觀察到異常磁滯曲線的發生。此種薄膜結構除了存在著特殊磁矩翻轉行為的特性之外，還具有強的界面交互耦合作用力。隨著鈷/鉑多層膜或鋱鐵鈷薄膜的垂直異向性的增加，此界面交互耦合作用力亦隨之增加。

關鍵字

鈷/鉑多層膜 ； 鋱(鐵)鈷薄膜 ； 磁交互耦合作用

並列摘要

The work focuses on the magnetic exchange coupling between Co/Pt multilayers and Tb(Fe)Co films.
Perpendicular spin-valves composed of Co/Pt multilayers and CoFe/TbCo bilayer were fabricated. The perpendicular GMR ratio of 4.8 % was obtained with the current-in-plane measurements. The interlayer coupling increased with increasing the net magnetization of CoFe/TbCo. A perpendicular pinning structure was proposed which possessed a high perpendicular coercivity (7 kOe) but zero net moment. Consequently, the interlayer coupling between free and pinned layers can be significantly suppressed. This perpendicular pinning structure can be potentially used for high-density perpendicular magnetic random access memory (MRAM) cells.
In addition, the oscillatory perpendicular interlayer coupling field and strength as a function of Ru spacer thickness were studied for samples with the [Co/Pt]5/Co/Ru/Co/TbCo structure. For Ru thickness in the range of 0.5-1 nm, a strong antiferromagnetic (AF) coupling (J~0.38 erg/cm2) was observed. When AF coupling existed, the coercivity of Co/TbCo bilayers was enhanced because the Co/Pt multilayers stabilized the magnetization direction of Co/TbCo. Consequently, oscillatory coercivity of Co/TbCo with Ru thickness was also observed. Since the magnetization direction of the Co-sublattice in TbCo can be tuned by adjusting composition or measuring temperature, the direction of the shifted minor loop of Co/Pt multilayers can be varied accordingly while keeping the same Ru thickness. Besides, in the perpendicular interlayer coupling of the [Co/Pt]5/Co/Ru/Co/TbCo samples, the canting angles of Tb and Co moments are determined by X-ray magnetic circular dichroism. The results displayed that the interlayer exchange coupling oscillates and aligns Co and Tb moments in opposite directions. In consequence, the canting angles of the Tb and Co moments correlate with the strength of the interlayer coupling and agree with our theoretical calculations as well. The opposite alignment on the TbCo sublattice magnetizations from the interlayer coupling cannot be viewed as an effective magnetic field and thus is unique with potential applications for spintronics devices.
Finally, I demonstrated the strong interfacial exchange coupling exists between Co/Pt multilayers and TbFeCo films with perpendicular magnetic anisotropy, which resulted in anomalous hysteresis loop. In addition, the interfacial exchange coupling can be increased by increasing the perpendicular magnetic anisotropy of Co/Pt multilayers or TbFeCo layer.

並列關鍵字

Co/Pt multilayers ； Tb(Fe)Co films ； magnetic exchange anisotropy

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