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  • 學位論文

銅取代鈷對L11介穩態鈷鉑薄膜結構及磁性質之效應

Effect of Co replacement with Cu on structure and magnetic properties of metastable L11 CoPt thin films

指導教授 : 郭博成
共同指導教授 : 許仁華(Jen-Hwa Hsu)

摘要


垂直磁記錄的方式已然成為未來記錄媒體的趨勢,在提升記錄密度的同時現有的記錄材料面臨其超順磁的物理極限,尋找具備高磁晶異相能的替代材料成為首要的重要工作。L11-CoPt的材料因為具備高磁晶異向能(Ku = 3.7 × 107 erg/cm 3)與極低的序化溫度(200℃),故為高潛力的磁記錄媒體候選材料,亦為本研究的主題。L11-CoPt,為一菱體晶(rhombohedral)的構造,其Co與Pt的原子層在晶體內以交替的方式沿[111]的方向堆疊,是CoPt合金相圖上不存在之介穩態,也是CoPt合金相中最晚被發現的(1997)。為了提升L11-CoPt的矯頑磁力,本實驗藉由在L11-CoPt中添加Cu取代Co的方式,在L11-CoPt中形成非磁性相的L11- CuPt,來達成此一目標。本研究使用超高真空磁控濺鍍的方式,在真空度5 × 10-8 torr下進行雙靶(Co與Pt)與三靶(Co、Pt與Cu)的共鍍,並以兩種薄膜厚度:20 nm與50 nm,故改變成份與臨場退火溫度的情況下當作實驗組與對照組討論之。 實驗室先前的研究指出,L11-CoPt較佳的晶體結構與磁性質可在製程溫度350℃的情況下得到,所以本研究以兩種不同的薄膜厚度在該溫度下去改變L11- (CoCu)Pt/MgO(111)的薄膜成份,發現在Co:30 at.%、Pt:47 at.%與Cu:23 at.%的成份下薄膜有其最佳的垂直的矯頑磁力與角型比,發現20 nm的薄膜垂直矯頑磁力由1.1 kOe提升到1.5 kOe,垂直角型比維持在0.9,水平矯頑磁力由0.5 kOe降到小於0.1 kOe。50 nm的薄膜垂直矯頑磁力由1.1 kOe提升到2.2 kOe,垂直角型比由0.35提升到0.97,水平矯頑磁力由1.4 kOe降到小於0.1 kOe。磁區研究發現Cu的取代使得平均磁域尺寸變小,穿透式電子顯微鏡結果發現明顯成份偏析現象,証明非磁性相L11-CuPt或CoCu的存在,而此結構造成磁化過程中磁域壁移動的阻礙,故增加垂直方向的矯頑磁力。而降低 L11-CoPt 水平方向的矯頑磁力,則意味著L11-(CoCu)Pt沿[111]方向排列的完美度的提升。 L11-CoPt是目前發現高Ku的材料中具有最低序化溫度者,彰顯了其於新一代垂直磁記錄媒體應用上的高度潛力,本研究証實Cu的添加可增加此一材料的垂直矯頑磁力並減少了水平矯頑磁力,更進一步提升了L11-CoPt的實用性。

關鍵字

鈷鉑薄膜 結構 磁性質

並列摘要


Due to increasing recording density toward 1 Tbit/inch2, currently-used perpendicular magnetic media encounter a physical limitation arising from superparamagnetism due to the reduction of grain size to several nanometers. Replacing the recording material with high magnetocrystalline anisotropy (Ku) materials becomes an imminent issue. L11-CoPt, a recently discovered metastable phase of CoPt having a rhombohedral lattice and consisting of alternatively stacked Co and Pt closed-packed atomic planes along [111], exhibits great potential owing to its high Ku of about 3.7 × 107 erg/cm3 and low formation temperature of 200℃. In this study, we replace some Co atoms in L11-CoPt with Cu to modify the microstructure and magnetic properties because L11 phase is thermodynamically stable in CuPt. (Co1-xCux)50Pt50 thin films with thickness of 20 nm and 50 nm were prepared using magnetron co-sputtering with background vacuum better than 10-8 torr on MgO(111) substrates with 0 ≦ x ≦ 1. Our results show a significant enhancement in out-of-plane coercivity (Hc⊥) from 0.1 to 1.9 kOe for 20-nm-thick films and 0.2 to 2.2 kOe for 50-nm-thick films with x = 23, respectively. This increase accompanies a reduction of in-plane coercivity (Hc//) from 0.5 to 0.02 kOe and from 1.4 to 0.07 kOe for films with thicknesses of 20 and 50 nm respectively. Reduced magnetic domain size from about 500 nm to 100 nm suggests that the enhanced Hc⊥ results from domain wall pinning mechanism. TEM microstructure analysis confirms a nanometer-scaled compositional segregation, forming Co-Pt rich and Cu-Pt rich regions. The nonmagnetic Cu-Pt precipitates may act as pinning sites to confine the domain size and block the domain wall motion. The results demonstrate that replacing Co by Cu effectively increases the perpendicular magnetic properties of L11-CoPt phase, which further support the possibility to use L11-CoPt in the future high-density recording medium.

並列關鍵字

Co Cu replacement structure magnetic properties L11

參考文獻


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被引用紀錄


李龍傑(2012)。第三元素添加對L11 CoPt薄膜之磁性質及微結構研究〔碩士論文,元智大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0009-2801201415011578

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