FePt/Os多層膜之顯微結構及磁性質研究

Study of microstructures and magnetic properties of FePt/Os multilayer films

陳士元(Shih-Yuan Chen)

指導教授 ： 吳振名 ； 姚永德

國立清華大學/工學院/材料科學工程學系/博士(2010年)

摘要

本論文主要以直流磁控濺鍍的方式製作FePt/Os多層膜系統及研究其特性。近年來許多有關鐵磁性材料透過非磁性物質產生交換藕合與其巨磁阻(gaint magnetoresistance)效應的研究，例如：Fe/Cr、Co/Ru、Co/Cr這些系統已經被廣泛的探討。我們以FM/Os/FM (FM=FePt, CoFe, Co, Fe, CoFeB, CoFeC)三層膜系統，改變中間層(Os)厚度來討論三層膜系統的磁阻效應與隨Os厚度變化出現的磁藕合行為與磁阻率的變化。又成長於陽極氧化鋁基板之FePt薄膜，我們透過SEM觀察，研究FePt薄膜於氧化鋁基板上的成長過程與機制，增加Au緩衝層對改善fct-FePt序化程度、提高矯頑力、降低序化溫度等有顯著的效果。針對FePt/Os多層膜之磁性質與微結構研究，我們以具高融點的貴金屬Os作為插入層來探討成長於玻璃基板與矽基板上的FePt/Os多層膜在高溫退火時的熱穩定性、薄膜層間的相互擴散、微結構和磁性質之研究。FePt/Os多層膜藉由非磁性層Os的間隔，使得晶粒度有效減小，並顯著提昇矯頑磁力(Hc)。而適量Os的添加，對於穩定FePt晶粒邊界與介面亦有很大的助益，使得晶粒表面異向場的減小達到最少。對Si(100)//[FePt(100nm)/Os5nm]薄膜而言，有或沒有Os緩衝層於熱處理700°C下的矯頑磁力值相差約9.3kOe。而實驗中證實Os緩衝層在高溫退火下可以有效阻擋矽基板的矽化反應及磁性層與磁性層間地相互擴散，即使Os間隔層的厚度只有1nm，仍可有效阻擋層與層間的擴散效應，並有效提高薄膜結構的熱穩定性與硬磁性質。Os插入層亦可控制FePt的晶粒大小及限制晶粒成長方向沿厚度二維方向成長。FePt薄膜的平均晶粒尺寸大小和L10硬磁相可藉由熱處理溫度和FePt膜每層厚度的調整而得到控制，並藉此提高矯頑磁力，成為良好超高密度磁記錄媒體的硬磁性材料。

關鍵字

FePt ； Osmium ； magnetic

並列摘要

The FePt/Os multilayer flims were deposited on Si(100) and glass substrates with/without a Os spacer layer at room temperature by dc-magnetron sputtering. The oscillation of the interlayer exchange coupling as a function of the Os spacer thickness and the GMR (giant magnetoresistance) effect has been widely studies in recent years. For example, Fe/Cr, Co/Ru, Co/Cr systems have been extensively discussed by different authors. The study of magnetoresistance and interlayer coupling of FM/Os/FM trilayer films (FM = FePt, CoFe, Co, Fe, CoFeB, CoFeC), the FM/Os trilayers films with suitable spacing layer (Os) thickness have been prepared on Si(100) substrates. We report the oscillation behavior of antiferromagnetic coupling as a function of the Os thickness and the magnetoresistance effect. The mechanism and growth process of FePt film on a membrane of anodized aluminum oxide have been studied by SEM observation. The additional Au buffer layer will promote the ordering process of FePt films, reduce ordering temperature and enhance the coercivity. For effects of Os inserted layers on the microstructure and magnetic properties of the FePt films, The thermal stability, interlayer diffusion, microstructures and magnetic properties of FePt(100nm) single-layer and multilayer FePt/Os films on Si(100) and glass substrates with/without a 10-nm-thick Os underlayer have been studied as functions of the annealing temperatures between 400 and 800°C. The insertion of a thin Os layer into the FePt and Si(100) interface results in better thermal stability. No diffusion evidence was found in samples with a thin Os layer and t ≧ 1 nm after a post-annealing procedure, as seen from X-ray, transmission electron microscopy, and magnetic studies. The Os underlayer can effectively prevent the diffusion of the intermixing between the FePt layer and the Si(100) substrate for temperatures up to 700°C. The FePt/Os multilayer films showed enhanced coercivity significantly due to the reduced grain size. The texture of hard magnetic layers and the grain size of the multilayer films can be well controlled by both annealing temperature and thickness of the FePt layer by an Os space layer. The enhancement of Hc can be understood from the fact that for a FePt film with an Os spacer layers, the increasing number of Os layer will inhibit the two-dimensional grain growth at the thickness direction of FePt films and enriches the grain boundary. We have experimentally demonstrated that even with a very thin 1 nm Os spacer layers, the [FePt(x)/Os(t)]n multilayer films can exhibit good hard magnetic properties and are attractive candidates for ultrahigh density magnetic recording media.

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