改變轟擊電壓與氧含量對於MgO/NiO/Ni3Fe與SiO2/NiO/Ni3Fe微結構與交換偏壓的影響

The effect of modifying the bombardment voltage and oxygen content on microstructures and exchange biases of MgO/NiO/Ni3Fe and SiO2/NiO/Ni3Fe

黃以陞(Yi-Sheng Huang)

指導教授 ： 歐陽浩

國立清華大學/工學院/材料科學工程學系/碩士(2013年)

https://doi.org/10.6843/NTHU.2013.00025

摘要

本實驗藉由雙離子束濺鍍系統(dual ion beam deposition system，DIBD)鍍膜底層反鐵磁NiO (16nm)以及鐵磁層Ni3Fe(11nm)，基板為Si(100)方向接著經過廠商處理成長出90 nm的SiO2與MgO(110)單晶基板。我們改變輔鍍射頻離子源的轟擊電壓(VRF=100、200)，固定氧流量為0.3sccm，固定氬氣流量為2.5sccm以及固定射頻離子源的轟擊電壓(VRF=100)氬氣流量為2.5sccm、改變氧流量(0.2、0.3、0.4 sccm)。在室溫的情況下進行鍍膜沉積。我們可以從HRTEM( high resolution transmission electron microscope )分析中發現在SiO2基板中NiO與Ni3Fe主要優選方位為(111)(200)與(220)方向與XRD結果一致。當轟擊電壓從100V 10.71%O2提升為200V 10.71%O2時，我們從XRD峰值的面積可以發現轟擊電壓為100V時I220/ I111=0.42，當轟擊電壓為200V時I220/ I111=0.68，也就是當轟擊電壓變大時，其優選方位會從(111)轉變為(220)，結構上的改變我們也從HRTEM中可以清楚看到，當轟擊電壓為100V時，其磁易軸方向有傾向於垂直介面的方位排列，與平行膜面的夾角為55.95゜，但在轟擊電壓提高為200V時，磁易軸的方位開始偏移直介面，與平行膜面的夾角為44.59゜，並且我們估算100V與200V 10.71%O2在NiO/Ni3Fe介面粗糙度，可以發現在100V SiO2中粗糙度為9.1 Å、200V為7.3 Å，在MgO基板上100V時粗糙度為3.9 Å、200V為2.6 Å，由此可發現當轟擊電壓上升時NiO/Ni3Fe介面會被轟的較為平坦，然而當氧含量降低到100V 7.41%O2時，在SiO2基板反鐵磁層中會有部分鐵磁成分Ni鑲嵌在NiO 基地裡，但在MgO(110)基板中並沒有在反鐵磁中發現鐵磁Ni的成分。
在MgO(110)基板中我們成功製備了100V 10.71 %O2 、200V 10.71% O2以及100V 7.41 %O2，從HRTEM的分析結果可以看到其zone軸為[001]並且成長方向為垂直介面(110)的方向進行磊晶成長，也因此我們限制了其優選方位。
我們藉由VSM (vibrating sample magnetometer)和SQUID(superconducting quantum interference device)去量測100V 10.71% O2 與200V 10.71% O2在SiO2與MgO(110)上的交換偏壓值，發現在SiO2基板上隨著轟擊電壓提高交換偏壓值上升是由於結構上的變化導致磁易軸的轉變，而在MgO基板上結構上並無改變，因為粗糙度的關係使得轟擊電壓提高交換偏壓值降低。

關鍵字

交換偏壓 ； 雙離子束濺鍍系統 ； NiO/Ni3Fe雙層膜 ； 穿隧式電子顯微鏡

並列摘要

This thesis explains the exchange bias and microstructure on both MgO(110) single crystal and SiO2 substrate, using different bombardment voltage and different O2/Ar ratio to deposit antiferromagnetic NiO and ferromagnetic Ni3Fe. We deposit 16nm underlayer (antiferromagnetic NiO) and toplayer(ferromagnetic Ni3Fe) by dual ion beam deposition system. The substrates are 90nm SiO2 grew out from Si(100) and MgO(110) single crystal. We use different bombardment voltages of RF ion source (VRF=100 and 200), and we control two variables: the oxygen flow is 0.3sccm and the argon flow is 2.5sccm. In another experiment, we use different oxygen flows (0.2, 0.3 and 0.4sccm), and we control two variables: the bombardment voltage VRF is 100 and the argon flow is 2.5sccm. All of these depositions are done under normal temperature.
From the HRTEM(high resolution transmission electron microscope analysis), the main preferred orientations of NiO and Ni3Fe are (111), (200) and (220) on the SiO2 substrate. The result from HRTEM is consistent to that from XRD. From the areas of XRD peaks, we find that with 10.71% O2, I220/ I111 ratio is 0.42 when the bombardment voltage is 100V; however, when the bombardment voltage rises to 200V, I220/ I111 ratio becomes 0.68. This result shows that as bombardment voltage rises, its preferred orientation changes from (111) to (220). Besides, we also find obvious changes on the structure from HRTEM. When the bombardment voltage is 100V, the easy axis tends to be more perpendicular to interface (the angle between easy axis and parallel interface is 55.95。) ; however, when the bombardment voltage rises to 200V, the easy axis shifts away (the angle between easy axis and parallel interface becomes 44.59。). Moreover, we also calculate the interface roughness between NiO and Ni3Fe with 10.71% O2. On the SiO2 substrate, when the bombardment voltage is 100V, the roughness is 9.1 Å; when the bombardment voltage is 200V, the roughness is 7.3 Å. Nevertheless, on the MgO substrate, when the bombardment voltage is 100V, the roughness is 3.9 Å; when the bombardment voltage is 200V, the roughness is 2.6 Å. This result shows that as the bombardment voltage rises, the interface roughness decreases. In the experiment with 7.41% O2, we find that on the SiO2 substrate, there is ferromagnetic Ni in the antiferromagnetic layer (NiO). However, on the MgO substrate, this phenomenon doesn’t happen.
In the MgO substrate, we deposit 100V 10.71 %O2, 200V 10.71% O2 and 100V 7.41 %O2. From the result of HRTEM, we find that the zone axes of them are [001] and their growing directions are perpendicular to the interface with (110) orientations, which are epitaxial growth. Therefore, we confine the preferred orientations.
We measure the exchange biases of 100V 10.71% O2 and 200V 10.71% O2 on both SiO2 and MgO(110) through VSM (vibrating sample magnetometer) and SQUID(superconducting quantum interference device). We find that on the SiO2 substrate, because the changes on the structure makes the easy axis shift, exchange bias increases when the bombardment voltage rises. However, on the MgO substrate, because there is no change on the structure, we conclude it is the roughness that matters. The roughness makes the exchange bias decreases when the bombardment voltage rises.

並列關鍵字

Exchange bias ； Dual ion beam deposition system ； NiO/Ni3Fe bilayer ； High resolution transmission electron microscope

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