利用一階迴轉曲線及磁圓偏振光譜針對L10-FePt/Ni雙層膜翻轉行為之探討

Abstract

近來，因磁記錄媒體密度需求不斷提升，具有高垂直磁晶異向性材料被廣泛地研究。含有軟、硬磁層所組成之複合式交換偶合之方式製作具有垂直異向性之磁性膜將能克服在磁記錄媒體在發展上的瓶頸。甚至可以透過調整軟、硬磁層的性質、比例等，達到各種不同的磁性質需求。其中，軟、硬磁層間交互作用力是影響整個磁化翻轉機制的關鍵，而磁化翻轉機制則決定了磁記錄媒體的功能性。因此，能夠提供量測軟、硬磁層連接後的磁化翻轉過程的工具是非常重要的。 本實驗結合了磁圓偏振光譜與一階迴轉曲線技術來探討一系列Ni/L10-FePt複合式交換偶合媒體之磁化翻轉特性。其中，磁圓偏振光譜能夠探測軟、硬磁層中特定元素所產生的磁貢獻量；一階迴轉曲線則能量測磁化翻轉之分布圖、各種磁相之狀態以及交互作用力的分布情況。 研究結果顯示，在介面處之交互作用將會造成磁區壁難以穿越軟、硬磁層介面，而軟磁層厚度的不同將導致磁區壁穿越軟、硬磁層介面能力的差異。此外，透過翻轉場分布的分析，可從磁滯曲線中分解出各個磁化翻轉步驟，並進一步解釋其物理意義。 本研究結果對軟、硬磁層間交互作用有更深入的了解，並可運用此交互作用進而改變類似結構之材料系統特性，製備未來所需的磁性薄膜。

Magnetic thin films with strong perpendicular anisotropy are intensively studied due to the increasing demand in high-density recording media. Perpendicular magnetic films with an exchange coupled composite (ECC) structure containing soft and hard layers offer the possibilities to satisfy many conflicting requirements in the world of magnetic recording. Especially, its flexibility of tuning the soft/hard layer properties plays as a versatile toolbox that provides all kinds of degree of freedom to achieve that goal. The magnetization reversal is one of the critical mechanisms determining a recording medium’s functionality, where the soft-hard layer interactions predominantly drive the whole mechanism. Characterization tools that can precisely monitor the reversal processes in various soft-hard combinations are highly desired in this field. In this study we enlisted a combination of x-ray magnetic circular dichroism (XMCD) and first order reversal curves (FORC) to explore the switching characteristics of a series of Ni/L10-FePt ECC, where XMCD probed magnetic contributions from soft/hard layers with element-specificity, while FORC provided information such as a full mapping of magnetic switching, coexistence of various magnetic natures, and the distribution of interaction field. The study points to strong sensitivity of interfacial interactions to the attendant phenomenon, such as different levels of domain-penetration from soft to hard layers by manipulating one layer through the other. By operating sophisticated switching field distribution (SFD) analyses, we further decomposed the major hysteresis loop into multiple switching components to further expound the physics behind the theme. The results open up opportunities to tailor the properties of similar systems by manipulating the soft-hard interdependency because of a deeper understanding of the subject matter.