Co100-xPtx單層薄膜與Co100-xPtx/Ag雙層薄膜之顯微結構與磁性質研究

Abstract

本研究利用直流磁控濺鍍在玻璃基板上鍍製Co100-xPtx ( x = 20~70 )(25 nm)單層合金薄膜及Co100-xPtx ( x = 20~70 )(25 nm)/Ag(30~150 nm)雙層合金薄膜，觀察其顯微結構與磁性質之變化。 單層Co-rich CoPt薄膜在300℃退火後為hcp相，具有較大之磁滯曲線及較佳之垂直膜面磁性質；單層CoPt薄膜在700℃退火30分鐘後由低溫之fcc相轉為L10序化相，可以得到較佳之磁性質；單層Pt-rich CoPt薄膜在500℃退火30分鐘後為fcc相，具有較好之垂直膜面磁性質。 在300℃真空退火後，由於Co-rich CoPt/Ag(30~150 nm)發生由hcp轉為fcc之相變化使得磁性質較原本單層Co-rich CoPt薄膜不理想。在600℃真空退火後，CoPt/Ag(30~150 nm)雙層薄膜有序化之L10硬磁相出現並具有垂直膜面方向磁異向性，在引入Ag底層後序化溫度較CoPt單層薄膜降低約100℃。CoPt(25 nm)/Ag(30 nm)薄膜於700℃退火30分鐘後有較佳之垂直膜面方向磁性質，Hc⊥為16.6 kOe、Hc//為10.5 kOe，S⊥為0.87、S//為0.4。在700℃真空退火後，Pt-rich CoPt/Ag(150 nm)雙層合金薄膜具有垂直膜面磁異向性，Hc⊥為6.9 kOe、Hc//為5.4 kOe，S⊥為0.75、S//為0.48，這是由於具有相同晶體結構但不同晶格常數的Co-rich及Pt-rich CoPt微細晶粒偏析在Ag3Pt晶界上，晶格不匹配產生之應力破壞了立方晶的對稱性使其具有單軸磁異向性。

The magnetic properties and microstructure of 25-nm-thick Co100-xPtx ( x = 20~70 ) alloy thin films grown on glass substrate as well as on 30~150 nm Ag under layer were investigated. These metal films were deposited by DC sputtering at a base pressure about 5×10-7 torr. The Co-rich CoPt single-layer alloy thin film with hcp phase after annealing at 300℃ shows large hysteresis loop and better out-of-plane magnetic properties. CoPt single-layer alloy thin film with L10 phase after annealing at 700℃ shows better magnetic properties. For Pt-rich CoPt single-layer alloy thin film with fcc phase after annealing at 500℃ shows better magnetic properties. After 300℃ post vacuum annealing, the phase of Co-rich CoPt/Ag(30~150 nm) alloy thin film will change from hcp to fcc and magnetic properties become worse than Co-rich CoPt single-layer alloy thin film. After 600℃ post vacuum annealing, CoPt/Ag(30~150 nm) alloy thin film shows L10 hard magnetic phase and out-of-plane magnetic anisotropy. The ordering temperature is 100℃lower than that of CoPt single-layer alloy thin film after inducing Ag under layer. The 700℃ annealed CoPt(25 nm)/Ag(30 nm) thin film improves magnetic properties, Hc⊥ = 16.6 kOe, Hc// = 10.5 kOe, S⊥= 0.87, and S// = 0.4 . After 700℃ post vacuum annealing, Pt-rich CoPt/Ag alloy thin film shows out-of-plane magnetic anisotropy by segregation of small Co-rich and Pt-rich CoPt grains on the grain boundary of Ag3Pt, those have the same lattice structure but different lattice parameter, and the stress of lattice mismatch breaks the symmetry of the cubic phase, so, presenting uniaxial magnetic anisotropy . The magnetic properties of 700℃ annealed Pt-rich CoPt/Ag(150 nm) alloy thin film are Hc⊥= 6.8 kOe, Hc// = 5.3 kOe, S⊥ = 0.75, and S// = 0.48 .