請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/23208
標題: | 低維度鐵磁-反鐵磁超薄膜系統之垂直磁異向性與交換耦合之研究 Interrelation between Perpendicular Magnetic Anisotropy and Exchange Coupling in Low Dimensional Ferromagnetic-Antiferromagnetic Ultrathin Film Systems |
作者: | Bo-Yao Wang 王柏堯 |
指導教授: | 林敏聰 |
關鍵字: | 低維度,磁性超薄膜,反鐵磁性,垂直磁異向性,交換耦合,自旋翻轉現象, Low dimension,magnetic ultrathin film,antiferromagnetism,perpendicular magnetic anisotropy,exchange coupling,spin-reorientation transition, |
出版年 : | 2009 |
學位: | 博士 |
摘要: | 由於維度縮小所造成在磁性上的奇特行為,及未來在奈米元件、垂直儲存上的應用潛力,低維度下具有鐵磁-反鐵磁交換耦合的結構在近年來受到廣泛的興趣及討論。本論文藉由觀測巨觀的磁滯曲線及微觀的磁疇來探討低維度磁性超薄膜中,垂直磁異向性與鐵磁-反鐵磁交換耦合之間的相互關係。在論文的第一部份中,我們在鐵/錳/銅三金及鎳鐵(Permalloy)/錳/銅三金機版雙層超薄膜系統中,發現一種有別於以往且獨特的垂直磁異向性。透過對實驗及理論模型的分析,我們證實其機制是來自於鐵磁-反鐵磁之間的交換耦合。因著其有趣且獨特的特性,在論文第二部份中,我們進一步定量的去探討反鐵磁面心立方錳(fcc-Mn)超薄膜的自旋相關長度(spin-correlation length ξ) 以及臨界指數(critical exponent λ)。這些重要的物理量除了可提供上述兩系統隨厚度變化的磁異向能外,更可以預測其他材料、例如鈷以及鎳與反鐵磁面心立方錳之間的交換耦合,以及其磁異向行為。其預測結果與後來的實驗結果是相吻合的。在論文第三部份中,我們將研究的範圍延伸至類面心立方錳。並藉由比較實驗結果以及理論計算來探討類面心立方錳的晶格結構、交換耦合,與自旋組態之間的關係。結果顯示面心立方錳傾向提供鄰近鐵磁層垂直異向性的交換耦合(out-of-plane oriented exchange coupling)。然而對於垂直晶格被壓縮的面心立方的錳(fct-Mn)來說,則是傾向提供鄰近鐵磁層平行膜面方向的交換偏耦合(in-plane exchange bias)。進一步利用光電子顯微鏡,我們觀察到當較厚且具有平行膜面磁異向性的鐵覆蓋於厚度連續變化的面心立方錳上時,其磁疇的磁性方向會隨著面心立方錳厚度的變化,而產生震盪的行為。這種震盪可能反映出面心立方錳仍具有平行於膜面方向上磁性結構之共存態。在論文的第四部份,在具有相似的晶格結構條件之下,我們比較鐵/面心立方錳/銅三金以及鐵/面心立方錳/面心立方鐵/銅三金超薄膜系統。我們發現位於最下層具有垂直方向磁性的2.5個原子層的鐵可以在其有效居禮溫度之下,透過交換耦合強化其反鐵磁面心立方錳的的磁異向性,進而導致最上層鐵超薄膜磁矯頑力的增加、以及由平行膜面至垂直膜面的自旋翻轉行為。 Low dimensional ferromagnetic (FM) - antiferromagnetic (AFM) exchange coupling systems attract much interest not only due to their novel magnetic behaviors with reduced dimensionality, but also for their potential applications in nanodevice and perpendicular storage. The work of this dissertation focuses on the study of the interrelation between perpendicular magnetic anisotropy and FM-AFM exchange coupling in low dimensional FM/AFM ultrathin film systems from both macroscopic (magnetic hysteresis-loop) and microscopic (magnetic domain) approaches.In the first part of this dissertation, a new kind of perpendicular magnetic anisotropy in Fe and permalloy(Py)/Mn/Cu3Au(001) ultrathin bilayer systems is presented. Through the experiments together with theoretical analysis, we demonstrate that the mechanism is driven by the FM-AFM exchange coupling. Due to such great interesting and unique capability for the AFM Mn ultrathin film with an facecenter-cubic (fcc) phase, in the second part, we quantitatively investigate the spin-correlation length (ξ) and critical exponent (λ) of AFM fcc-Mn ultrathin film. The extracted invariant physical quantities not only provide the thickness-dependent magnetic anisotropy energy of Fe/Mn and Py/Mn ultrathin bilayers, but also could be used to estimate that for other Co/Mn and Ni/Mn systems, in which the predicted behaviors were found to be consistent with further experiment results, respectively. In the third part, we extend our interesting to the fcc-like Mn, the correlation between crystalline structure, exchange coupling with adjacent FM layer and AFM spin configuration of fcc-like Mn ultrathin films were investigated by comparing experiments with theoretical calculations in literature. We demonstrate that the out-of-plane oriented exchange coupling and the in-plane exchange bias coupling, characterized by the presence of in-plane to perpendicular spin-reorientation transition (SRT) and in-plane exchange bias, dominate in FM/fcc-Mn and FM/fct-Mn ultrathin bilayers, respectively. Furthermore, for a thicker in-plane magnetic Fe film with a wedged-shape fcc-Mn underlayer, the in-plane magnetization direction of Fe layer was found to be continuously oscillating with the variation of Mn thickness at low temperatures. This result points out that fcc-Mn could still have a co-existed in-plane layered spin state resulting such oscillation behavior. In the fourth part, the magnetic anisotropy between single crystalline Fe/fcc-Mn/Cu3Au(001) and Fe/fcc- Mn/fcc-Fe/Cu3Au(001) ultrathin films are compared. With nearly invariant crystalline structures for the fcc-Mn and the topmost Fe layer between these two systems, we demonstrate that the presence of 2.5 ML fcc-Fe underlayer with perpendicular magnetic anisotropy could enhance the perpendicular magnetic anisotropy of adjacent Mn layers, leading to the significant enhancement of perpendicular coercivity and even in-plane to perpendicular SRT in the topmost Fe layer. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/23208 |
全文授權: | 未授權 |
顯示於系所單位: | 物理學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-98-1.pdf 目前未授權公開取用 | 3.24 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。