垂直磁異向性之Co56Pt44/Ag及Co80Pt20/Ag薄膜 磁性質與微結構的研究

Abstract

本研究以直流磁控濺鍍的方式鍍製Co100-xPtx/Ag、Co80Pt20/Ag合金等薄膜於康寧1737玻璃基板上，探討Ag底層及製程參數對Co100-xPtx合金薄膜之顯微結構、磁性質的影響。 Ag底層之引入可降低CoPt合金薄膜之序化溫度及促進其垂直磁異向性。Co56Pt44/Ag雙層膜經700oC退火 30分鐘後，薄膜之磁異向性由磁等向性轉變為傾向垂直膜面磁異向性，其垂直膜面矯頑磁力(Hc⊥)高達15.9 kOe、垂直膜面角型比(S⊥)為0.884。進一步加入Co56Pt44軟磁層於Co56Pt44硬磁層/Ag雙層膜上方，當軟磁層厚度超過2 nm後，薄膜的磁翻轉機制會由 single switching field轉變為two-step reversal processes。 常溫初鍍之單層Co80Pt20(25 nm)薄膜呈現磁等向性，僅加入Ru底層或僅加入Ag底層皆無法使其產生垂直膜面磁異向性。然而搭配100 nm Ag底層及30 nm Ru中間層後可獲得垂直磁異向性之Co80Pt20合金薄膜，其Hc⊥值可達4.53 kOe ，S⊥值為0.815。TEM明視野影像顯示，Co80Pt20磁性層之晶粒呈現柱狀及顆粒狀結構，其平均晶粒尺寸約為8.1 nm。進一步將Co80Pt20(25 nm)/Ru(30 nm)/Ag(100 nm)多層膜置於1 mTorr的環境下進行300 oC退火後，薄膜之垂直硬磁性可大幅提升，其Hc⊥及S⊥分別上升至5.04 kOe 及0.869，這些性質具備應用於高密度垂直磁記錄媒體的潛力。

In this study, an Ag underlayer is deposited on the 1737 Corning glass by dc magnetron sputtering, then the Co56Pt44 or Co80Pt20 alloy films is deposited onto the Ag layer. The effects of Ag underlayer and process parameters on the microstructure and magnetic properties of Co100-xPtx films are investigated. The ordering temperature of Co56Pt44 films can be reduced as Ag underlayer is introduced. Ag underlayer can also promote the perpendicular hard magnetic properties of the film. After annealing at 700oC for 30 min, the perpendicular coercivity (Hc⊥) and perpendicular squareness (S⊥) are increased to 15.9 kOe and 0.884, respectively. The Co56Pt44 soft layer is further added on the Co56Pt44 hard layer/Ag double-layered film. It is found that the magnetization reversal process of the films changes from a single switching field to a two-step reversal processes when the thickness of the soft layer is above 2 nm. Granular Co80Pt20 nano-grains having perpendicular coercivity of 4.53 kOe and perpendicular squareness of 0.815 can be achieved by dc sputtering Co80Pt20 (25nm) film onto Ru(30nm)/Ag(100nm)/Glass at ambient temperature. TEM cross-sectional images show that the columnar nano-grains with average width of 8.1 nm are observed in Co80Pt20 magnetic layer. When post-annealed the Co80Pt20/Ru/Ag/Glass multi-layer films in a vacuum of 1mTorr at a lower temperature of 300 oC for 30 min, both the perpendicular coercivity and perpendicular squareness of the film can be increased greatly to 5.04 kOe and 0.869, respectively. It has significant potential to be applied as the perpendicular magnetic recording medium.