Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/9517
標題: 氧含量對鎳鐵/氧化鎳奈米雙層薄膜之結構及磁性研究
Effect of Oxygen Contents on Structural and Magnetic Properties of NiFe/Ni-oxide Bilayers
作者: 郭仲儀
Guo, Zhong-Yi
關鍵字: Ni80Fe20/Ni-oxide bilayers;鎳鐵/氧化鎳雙層薄膜;magnetoresistance (MR) heads;ion-beam deposition technique;magnetoresistance behavior;雙離子束濺鍍技術;岩鹽結構;柱狀結構
出版社: 材料工程學研究所
摘要: 
本研究利用雙離子束濺鍍技術製備鎳-氧化鎳(Ni-NiO)複合薄膜及鎳鐵/氧化鎳[Ni80Fe20(20 nm)/Ni-oxide(9 nm)]雙層薄膜。研究重點為輔助離子束氧含量之變化(0%~33% O2)對結構及磁性質的影響。X光繞射(XRD)分析得知:鎳鐵 (Ni80Fe20) 薄膜之晶體結構為面心立方(f.c.c.),晶格常數a= 3.54 Å。鎳-氧化鎳複合薄膜方面:輔助離子束氧含量7% O2之薄膜,其組成為雙相之f.c.c.鎳(a= 3.52 Å)及岩鹽(rock-salt)結構氧化鎳(a= 4.21 Å)。當氧含量增加至33% O2,薄膜之結構由單一相之氧化鎳(a= 4.32 Å)所組成。穿透式電子顯微鏡(TEM)研究結果顯示:鎳鐵薄膜及鎳-氧化鎳薄膜之結構與XRD結果一致且晶粒尺寸介於5 nm~10 nm之間。TEM橫截面試片之明視野影像顯示:鎳鐵/氧化鎳雙層薄膜之生長模式為垂直於基材表面的柱狀結構。原子力顯微鏡(AFM)分析結果顯示:鎳鐵/氧化鎳雙層薄膜之表面粗糙度隨氧含量增加而增加。
磁性研究顯示,鎳鐵薄膜室溫之飽和磁化強度為Ms= 720 emu/cm3,矯頑場為Hc= 2 Oe,與塊材性質接近。當氧化鎳厚度由9nm增加至36 nm時,鎳鐵/氧化鎳雙層薄膜間之交換耦合效應與溫度存在一強烈的相依性:交換場強度隨溫度降低而增加,且在T= 150K時,此試片之交換場為Hex= -43 Oe。當鍍膜過程外加平行基材表面之磁場(Happ= 300 Oe),可使鎳鐵/氧化鎳雙層薄膜具有優異的室溫磁性質(Hc= 16 Oe,Hex= -45 Oe, |Hex/Hc|= 2.8)。當氧化鎳鍍膜過程之基材溫度為250 oC時,鎳鐵/氧化鎳雙層薄膜(Tsub= 250 oC)之交換場Hex=0 Oe,可能由於氧化鎳轉變為金屬鎳所致。
磁電傳輸性質方面,純鎳薄膜之電阻係數為28μm-cm。鎳-氧化鎳複合薄膜之電阻係數隨氧含量增加而增加。鎳-氧化鎳複合薄膜及鎳鐵/氧化鎳雙層薄膜均具有異方性磁電阻(Anisotropic magnetoresistance)性質。上述試片在室溫之總磁電阻率均小於2%。鎳鐵/氧化鎳雙層薄膜在T=298K和77K 之總磁電阻率皆隨氧含量增加而上升,NiFe/NiO(33% O2)試片具有最大之總磁電阻率(4.5%,T=77K)。

The exchange coupling between ferromagnetic (FM) and antiferromagnetic (AF) thin films has received increasing attention because it plays an important role in magnetoresistance (MR) heads or spin valves. In this study, the structural and magnetic properties of Ni80Fe20/Ni-oxide bilayers prepared by an ion-beam deposition technique have been investigated. XRD results have shown that Ni-oxide composite films (7% O2) in the assisted beam consisted of a mixture of f.c.c Ni (a=3.52 Å) and rock-salt NiO (a= 4.21 Å) phases. The expanded lattice constant (4.32 Å) of the pure NiO phase has been observed for films prepared with 33% O2 in the assisted beam. TEM micrographs revealed that the grain sizes of these Ni-oxide films range from 5 nm to 10 nm.
A strong temperature dependence of exchange field Hex was observed in the Ni80Fe20 (20 nm)/Ni-oxide (36 nm) bilayers whose magnitude increases with decreasing temperature. At T=150 K, the exchange field of this sample has been determined to be Hex~ -43 Oe. At room temperature, this Ni80Fe20/Ni-oxide bilayers exhibit good magnetic properties (Hc= 16 Oe,Hex= -45 Oe, |Hex/Hc|= 2.8 ), when applied a magnetic field (Happ.~ 300 Oe) during deposition.
Magnetotransport properties have shown that the pure Ni film exhibits a resistivity of 28μm-cm, and it increases with increasing oxygen contents in the assist beam. Both Ni-oxide composite films and Ni80Fe20/Ni-oxide bilayers exhibit anisotropic magnetoresistance (AMR) behavior. At T= 298K and 77K, the total MR ratio for Ni80Fe20/Ni-oxide bilayers increases with increasing oxygen contents. The Ni80Fe20/NiO (33% O2) bilayers exhibit a maximum total MR ratio of 4.5% (T=77 K).
URI: http://hdl.handle.net/11455/9517
Appears in Collections:材料科學與工程學系

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