Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/10119
標題: 單晶基板及離子束轟擊對氧化鎳/鎳鐵交換偏壓薄膜之效應
The effects of single crystalline substrates and ion-beam bombardment of exchange-biased NiO/NiFe bilayers
作者: 賴伯誠
Lai, Bo-Cheng
關鍵字: exchange bias
交換偏壓
ion-beam bombardment
離子束轟擊
出版社: 材料科學與工程學系所
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摘要: 本研究係利用雙離子束濺鍍系統製備氧化鎳(NiO)/鎳鐵(NiFe)雙層薄膜,並分成兩大部分: (I)於平行膜面施加一外加磁場(145 Oe),分別在不同基板上製備氧化鎳(20 nm)/鎳鐵(80 nm)雙層薄膜,以探討使用不同的基板對薄膜結構與磁性質所造成之影響;(II)利用輔助離子束以不同電壓對鎳鐵(18 nm)薄膜表面進行轟擊,並改變上層氧化鎳之厚度(5, 35nm),分別討論轟擊電壓及反鐵磁層厚度之效應,而此部分於無外加磁場下進行製程。 在基板效應部分,由結構分析中發現成長於MgO(111)單晶基板之雙層薄膜具有不同的從優取向。室溫之磁性質方面,鍍膜在SiO2基板上的雙層膜之矯頑磁力(Hc)約為2 Oe,且無明顯交換偏壓場(Hex ~ −2 Oe)。然而,使用MgO(100)、MgO(110)、MgO(111)和Al2O3(0001)、Al2O3(112 ¯0)單晶基板皆使氧化鎳/鎳鐵雙層膜之矯頑磁力增加,鍍在MgO(111)單晶基板上具有最大的矯頑磁力(~ 8 Oe),而對交換偏壓場則產生不同的結果,使用Al2O3單晶基板較MgO單晶基板能引發交換耦合效應,最大的交換偏壓場(~ 5 Oe)出現在鍍於Al2O3(112 ¯0)單晶基板之雙層薄膜。經由場冷至50 K,其磁性質顯示雙層膜鍍在Al2O3(112 ¯0)單晶基板上之矯頑磁力明顯增加至26 Oe,並且具有最大的交換偏壓場(Hex ~ −11 Oe)。 在離子束轟擊鎳鐵表面研究結果顯示,鎳鐵層厚度隨轟擊電壓上升而變薄(蝕刻作用),此可由X光繞射分析中NiFe(111)繞射峰減弱而得證。磁性質方面,氧化鎳厚度為5 nm之氧化鎳/鎳鐵雙層薄膜中,室溫和場冷至5K後皆無交換耦合效應的產生。然而將氧化鎳厚度增加至35 nm後,室溫中即具有交換偏壓場,在雙層膜界面未受離子束轟擊(Hex ~ −7 Oe)及轟擊電壓為70 V時(Hex~ −30 Oe)具有負交換偏壓場,而增加電壓至100 V以上均具有正的交換偏壓場(+Hex),且當電壓為130 V時有最大的正交換偏壓場(~ +40 Oe),矯頑磁力方面則隨著轟擊能量增強而增加。經場冷至5 K後,未受離子束轟擊之雙層薄膜具有最大的正交換偏壓場(~ +85 Oe),隨著離子束電壓增強,交換偏壓場逐漸降低並且其符號呈現正負值震盪的現象。
When spins at the interface between a ferromagnet (FM) and an antiferromagnet (AF) couple, a unidirectional anisotropy occurs, resulting in exchange bias. Our previous work on NiFe/NiO bilayers has shown that the exchange bias depends on the whole AF layer spin structures that have been altered with ion-beam bombardment during film deposition. Since exchange bias is dominated by interface magnetism, we wish to identify the dependence of the exchange bias on the interface microstructure by changing the deposition sequence. In this study, we have shown the effects of (1) different single crystalline substrates and (2) ion-beam bombardment on exchange-bias in NiO/NiFe bilayers. Firstly, different substrates showed at room temperature enhanced coercivities bilayers deposited on single crystalline MgO and Al2O3. However, when field cooling (12 kOe FC) the films to 50 K only the NiO(20nm)/NiFe(80nm) bilayer grown on a Al2O3 (112 ¯0) substrate exhibited an enhanced Hc (~ 26 Oe) as well as Hex (~ −11 Oe). Secondly, for different ion-beam bombardment energies (VEH) at room temperature a both positive and negative Hex was found in NiO(35nm)/NiFe bilayers, where the polarity of Hex depended on the energy used for Ar+ bombardment on the NiFe surface. The increased Hc with increasing VEH indicated that the NiFe layer was etched away with increasing Ar+ bombardment energies. In addition, the changes between magnetic easy and hard axis after ion-beam bombardment were revealed by their respective hysteresis loops. This magnetism is different from NiFe/NiO bilayers where the Ar+ bombardment was employed on the AF NiO surfaces. However, at 5 K under a 20 kOe FC process, a largest positive Hex (~ +85 Oe) was observed in NiO/NiFe (VEH= 0V) bilyers. Further, an oscillating Hex (between positive and negative) was found with increasing VEH. The dependence of the exchange bias field, Hex, with increasing VEH suggests strongly that the Ar ion-beam bombardment process may increase the spin canting in FM/AF interfaces (drop in Hex) or create uncompensated NiO spins (positive Hex), depending on the energy used. The change from +Hex to −Hex was likely due to the change in coupling (e.g FM to AF) at the interface.
URI: http://hdl.handle.net/11455/10119
其他識別: U0005-0906201112052000
文章連結: http://www.airitilibrary.com/Publication/alDetailedMesh1?DocID=U0005-0906201112052000
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