探討Co、Pt單層厚度變化對[Co/Pt]n多層膜的磁性質及微結構影響

Effect of Co and Pt layers thickness on magnetic properties and microstructure of [Co/Pt]n thin film

吳祥源(Hsiang-Yuan Wu)

指導教授 ： 孫安正

元智大學/工程學院/化學工程與材料科學學系/碩士(2012年)

摘要

L11相結構因其能在較低的製程溫度形成，可抑制晶粒成長並降低製程成本，且擁有充足的矯頑磁力(coercivity, Hc)及優異的垂直異向性能(Perpendicular Magnetic Anisotropy, Ku)，故近年來廣受討論。然此L11相結構目前都是以CoPt單層合金薄膜的方式製備，尚無研究以多層膜的方法鍍製，所以在多層膜製程的性質至今仍是無數據可參考。故本實驗利用超高真空多層膜濺鍍系統製備鈷/鉑[Cox/Pty]n多層膜，探討Co、Pt單層厚度(x與y)與週期數(n)改變對於低溫製備L11相的磁性質及微結構的影響。
本研究第一部份首先探討在改變工作溫度及底層添加對於薄膜性質的影響，並將Co、Pt單層厚度比例x：y定在4：3。從磁滯曲線可看出，室溫下直接將[Cox/Pty]n多層膜鍍在玻璃基板上時，會得到等向性未序化的A1軟磁結構。但是在加了一層Pt底層後，可使堆疊在上面的[Cox/Pty]n多層膜會沿著Pt(111)的優選方位做排列，使[Cox/Pty]n多層膜產生了明顯的垂直異向性。增加工作溫度至350 oC後，有利於Co、Pt原子擴散加速形成L11相結構，對於矯頑磁力的提升有明顯的效果，其最大值出現在[Co(1 nm)/Pt(0.75 nm)]3總厚度5.25nm時可達1.4 kOe。
第二部分主要是藉由改變Co、Pt單層厚度比例定在3：4。觀察比例改變對磁性質的影響。根據磁滯曲線的量測結果發現，較大的矯頑磁力同樣在厚度低時，其最大值出現在[Co(0.75 nm)/Pt(1 nm)]3 總厚度為5.25 nm時可達1.15 k Oe。而當Co、Pt單層厚度比例定在1：1時則出現了本實驗最大的矯頑磁力，其最大值為[Co(0.5 nm)/Pt(0.5 nm)]4 總厚度在4 nm可達2 kOe，依然是隨著厚度的增加其矯頑磁會降低。
由此實驗結果可以初步得知，藉由多層膜週期性(Periodicity)排列的特性，使其堆疊成接近單原子層距離的結構，降低原子擴散的距離，使Co與Pt的原子能快速移動至正確的晶格位置而形成L11合金相，所以改善磁性質。

關鍵字

多層膜 垂直異向性 矯頑磁力

並列摘要

L11 CoPt structure can be prepared at low temperature which can suppress the grain growth and reduce the equipment cost. Moreover, it has attracted a lot of attention in recent year due to the L11 structure has sufficient thermal stability and large perpendicular magnetic anisotropy. Up to now, the formation of L11 structure is, however, almost sputtered by CoPt single layer type, and the multilayer sputtering method was not investigated. In this study, we deposited [Cox/Pty]n multilayer at lower temperature in the ultrahigh vacuum system and discussed the influence of layer structure on magnetic property and microstructure of L11 CoPt thin film.
The first part of this study was focused on the effect of working temperature and underlayer on the CoPt film. Thickness ratio of Co and Pt layer was set at 4:3. [Cox/Pty]n multilayer films sputtered on glass at room temperture were isotropy, resulting form disorder A1 phase. After inserting the Pt underlayer, the atom orientation of the [Cox/Pty]n multilayer was transferred into c-axis, which showed perpendicular magnetic anisotropy in the film. When temperature was increased to 350 oC, the atoms mobility and diffusivity of Co and Pt atoms were improved and therefore obtained L11 phase, which resulted in enhancement of coercivity.
The last part was worked on thickness ratio and single layer thickness of Co and Pt layer, and total thickness of [Cox/Pty]n multilayer films were further investigated. The Hc of [Co(0.5 nm)/Pt(0.5 nm)]4 film has a higher value of 2 kOe in comparsion with other films.
From our results, it was demonstrated that the magnetic properties of the [Cox/Pty]n multilayer films were enhanced with decrease of diffusion length of Co and Pt atoms, which facilitated to formation of L11 structure.

並列關鍵字

multilayer perpendicular magnetic anisotropy coercivity

參考文獻

[30] 吳弘仁，雙離子束濺鍍系統及後退火處理製備鐵鉑/氧化錳雙層膜之微結構與磁性質研究，國立中興大學材料科學與工程學系研究所碩士學位論文(2011)

[51] 韓岱君，含碳化鐵奈米磁顆粒之非晶質碳膜其微觀結構、碳性質與磁阻的研究，國立成功大學物理所博士論文(2003)。

[4] 劉士賢，於玻璃基板製備(001) 單層 FePt 膜之研究，逢甲大學材料科學與工程學系碩士論文 (2011)。

[1] 許仁華、孫安正，奈米儲存發展與前景，物理雙月刊（三十卷二期）2008年四月，p.152-159。

[62] 許如宏、林鶴南。原子力顯微術於奈米加工之應用。物理雙月刊 25 (5) (2003) 620-631。