CoPt-ZnOx/ Ag複合磁記錄薄膜之顯微結構與磁性質研究

Abstract

本研究以直流磁控濺鍍的方式於室溫鍍製CoPt、CoPt/ Ag、CoPt/ ZnOx、(CoPt/ ZnOx)n、(CoPt)y-(ZnOx)1-y及(CoPt)y-(ZnOx)1-y/ Ag(y=5~50 vol%)等薄膜，探討Ag、ZnOx底層、ZnOx添加物及製程參數對CoPt薄膜之顯微結構、磁性質及其易磁化軸方向的影響。 關於CoPt/ Ag薄膜的製作，Ag底層引入後有降低CoPt薄膜序化溫度的效果，序化溫度從單層CoPt薄膜的600~700℃降至500~600℃之間，並且Ag底層有促進CoPt薄膜垂直膜面磁異向性的效果。Co56.42Pt43.58 (20 nm)/ Ag (30 nm)薄膜於700℃退火30分鐘後，具有較佳的垂直膜面磁性質，其垂直膜面矯頑磁力(Hc⊥)為17.6 kOe、平行膜面矯頑磁力(Hc//)為15.4 kOe、垂直膜面角形比(S⊥)為0.85、平行膜面角形比(S//)為0.51。 在CoPt/ ZnOx雙層薄膜方面，經調整製程參數後發現，當ZnOx濺鍍功率密度為2.81 watt/ cm2、厚度為30 nm時，會使20 nm的CoPt薄膜擁有最好的垂直膜面磁性質。(CoPt/ ZnOx)3多層薄膜經過700℃退火30分鐘後，會呈現垂直膜面磁異向性。 本研究同時利用ZnOx來製作具顆粒狀結構的CoPt薄膜，(CoPt)y-(ZnOx)1-y薄膜經過700℃退火30分鐘後，發現添加25 vol%的ZnOx會使薄膜序化度達到最好，此乃因ZnOx在高溫熱處理後，會留下孔洞和缺陷形成Co和Pt擴散的路徑，使CoPt薄膜更容易序化。之後將單層(CoPt)y-(ZnOx)1-y薄膜加上Ag底層，形成(CoPt)y-(ZnOx)1-y/ Ag雙層薄膜，在700℃退火30分鐘後，當ZnOx添加量為5 vol%時，因為造成CoPt晶粒之交互耦合作用下降，故Hc⊥值會上升，且由於ZnOx添加量較少，使CoPt薄膜與Ag底層之間的磊晶作用仍能保持，所以(CoPt)95(ZnOx)5/ Ag薄膜有最佳的垂直膜面磁異向性。當ZnOx添加量為50 vol%時，ZnOx會在CoPt和Ag的晶界析出，使CoPt與Ag被隔離並抑制晶粒成長，但50 vol%的ZnOx會使兩者之間的磊晶效果下降，因此此時薄膜的異向性呈現random。

In this study, the CoPt, CoPt/ Ag, CoPt/ ZnOx, (CoPt/ ZnOx)n, (CoPt)y-(ZnOx)1-y, and (CoPt)y-(ZnOx)1-y/ Ag films were deposited on glass substrates at room temperature by dc magnetron sputtering. The effects of Ag underlayer, ZnOx underlayer, ZnOx addition, and process parameters on the microstructure, magnetic properties, and magnetic easy axis of the film were investigated. The ordering temperature of CoPt films could be reduced from 600~700℃ to 500~600℃ as Ag underlayer was introduced. The introduction of Ag underlayer could promote the out-of-plane magnetic properties of CoPt films.The out-of-plane coercivity, in-plane coercivity, out-of-plane squareness and in-plane squareness values of Co56.42Pt43.58 (20 nm)/ Ag (30 nm) film which annealed at 700℃ for 30 minutes are 17.6 kOe, 15.4 kOe, 0.85 and 0.51, respectively. The CoPt/ ZnOx multilayer with ZnOx sputtering power density, 2.81 watt/ cm2, showed out-of-plane magnetic anisotropy after annealing at 700℃ for 30 minutes, and (CoPt/ ZnOx)3 multilayer also presented the out-of-plane magnetic anisotropy after annealing at 700℃ for 30 minutes. The ZnO target and the CoPt target were co-sputtered to form the granular CoPt films. The high ordering of (CoPt)75-(ZnOx)25 film could be obtained after annealing at 700℃ for 30 min. It suggests that ZnOx additives would leave vacancies and defects after annealing, which provides the diffusion path of Co and Pt atoms and improves the ordering of CoPt films. Finally, the 30 nm-Ag layer was introduced under the (CoPt)y-(ZnOx)1-y film and then annealed at 700℃ for 30 min. The larger out-of-plane coercivity of (CoPt)95-(ZnOx)5/ Ag film could be obtained because of the decrease of the exchange coupling. Besides, the ZnOx would precipitate at the grain boundaries of CoPt and Ag layers as the content of ZnOx additive increased to 50 vol%, which could isolate the CoPt and Ag grains and inhibit the grain growth of CoPt. ZnOx would reduce the epitaxial effect between CoPt and Ag layers and lead (CoPt)50-(ZnOx)50/ Ag film to the random orientation.