應用於圖樣化及熱輔助磁記錄之具(001)優選取向的序化鐵鉑交互彈簧磁體

(001)-oriented L10 FePt exchange spring magnets for bit-patterned and heat-assisted magnetic recording

廖容蔚(Jung-Wei Liao)

指導教授 ： 賴志煌

國立清華大學/工學院/材料科學工程學系/博士(2014年)

https://doi.org/10.6843/NTHU.2014.00107

摘要

圖樣化與熱輔助磁記錄媒體擁有記錄密度超過1 Terabits/in2的潛力，而具有(001)優選取向的序化鐵鉑交互彈簧磁體為實現其記錄媒體的重要基石。在本論文中我們首先在實驗上實現此交互彈簧磁體，進而在實驗與理論上研究其磁體內部的磁矩翻轉模式。實驗結果顯示在單一鐵鉑膜層中其序化伴隨著薄膜的團聚行為，導致於一序化但具有不規則孔洞的薄膜，無法利用其薄膜進一步製備圖樣化磁記錄媒體。藉由引入氧化鐵的覆蓋層我們可以在保有序化行為下抑制其薄膜團聚，成功地得到一連續、序化且具有(001)優選取向的鐵鉑薄膜。接著，我們使用原子自旋模型研究一具有軟磁邊緣的鐵鉑圖樣點內磁矩翻轉模式；其軟磁邊緣可能由於在圖樣化連續鐵鉑薄膜成奈米點的過程中產生的附加傷害而形成。計算結果顯示在不同的邊緣寬度下磁矩皆藉由成核的方式翻轉；隨著邊緣寬度的增加翻轉行為由個別的成核轉變成多個位置一起成核，而所需的成核磁場隨之降低然後飽和。在相對薄的軟磁邊緣下個別的成核行為可進一步由滴狀和反滴狀模型描述。最後，我們研究在具有不同軟磁層的居里溫度之序化鐵鉑交互彈簧磁體內磁矩翻轉行為；在熱輔助磁記錄媒體內其軟磁層的居里溫度影響高溫下熱導入寫入錯誤的大小，而軟磁膜層厚度的增加將降低加熱效率。研究結果顯示對於達成磁區壁輔助翻轉所需的軟磁膜層厚度和其居里溫度成正比，且其薄膜厚度將隨著寫入溫度地上升而進一步增加。由於增加的軟磁膜層厚度將犧牲熱輔助寫入所需的加熱效率，在保有足夠加熱效率的熱輔助寫入下將難以達成磁區壁輔助翻轉。所有結果建議著在圖樣化與熱輔助磁記錄媒體中為了保有其加熱效率，我們需引入一薄的軟磁層薄膜，而磁區壁輔助翻轉可能藉由軟磁邊緣的幫助來達成。

關鍵字

磁記錄媒體 ； 鐵鉑 ； 熱輔助 ； 圖樣化 ； 交互彈簧磁體

並列摘要

For bit-patterned and heat-assisted magnetic recording media, the essential basis is the (001) textured L10 FePt exchange spring magnet. In this dissertation we firstly realize this spring magnet and then investigate the corresponding magnetization reversal modes. We show that in a single-layered FePt film the L10 ordering is accompanied by the film agglomeration, resulting in the ordered but ruptured film. By introducing an FeOx capping layer we can suppress the film agglomeration while preserve the L10 ordering, leading to the desired continuous and (001)-oriented L10 FePt layer. Using the atomistic spin model we then investigate the magnetization reversal modes in the L10 FePt patterned dot with the soft magnetic edge, which could be caused by patterning damage. We show that the nucleation dominates the magnetization reversal at all studied edge-widths. As the edge-width increases the individual nucleation event, which can be described by the droplet and the antidroplet, turns into the multiple nucleation events, and the required nucleation field decreases and saturates. Finally, we investigate the magnetization reversal behaviors in L10 FePt exchange spring magnets with soft magnetic layers of varied Curie temperature (Tc), which are crucial for the thermally induced error. We show that for the domain-wall assisted reversal the increased Tc of the soft layer increases the required soft-layer thickness, which further increases at elevated temperatures. For the heat-assisted magnetic recording the increased soft-layer thickness sacrifices the heat efficiency and is therefore undesirable. All the results indicate that in the bit-patterned and heat-assisted recording media, a thin soft magnetic layer preserves the heat efficiency, and the soft magnetic edges with controllable properties could achieve the domain-wall assisted reversal.

並列關鍵字

Magnetic recording media ； FePt ； Heat-assisted ； Bit-patterned ； Exchange spring magnet

參考文獻

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