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標題: | 鐵在皺化鎢表面之表面形貌與磁性研究 Morphology and Magnetic Properties of Iron on Faceted Palladium over Tungsten(111) |
作者: | Yu-Chen Yeh 葉宥辰 |
指導教授: | 林敏聰 |
關鍵字: | 鐵,鎢,皺化,磁性,超薄膜, iron,tungsten,magnetic,ultra thin film, |
出版年 : | 2008 |
學位: | 碩士 |
摘要: | 由過去實驗得知,於鎢基板上鍍上約1層以上的鈀,Pd / W(111),並做適當的熱處理,將使表面皺化產生{112}面,在不同溫度退火(anneal)的樣品,表面的皺化金字塔(faceting pyramid)大小也不盡相同。本實驗於皺化鎢表面鍍上鐵,Fe / faceted Pd / W(111),觀察此低維度極度不平整表面,將對鐵磁性材料造成何種影響。由低能量電子繞射的實驗可知,室溫或低溫下,鐵未能在皺化鎢表面上有序成長,然而我們的真空腔並未裝設如電子穿隧顯微鏡等系統,故未能確定鐵在皺化鎢表面上的結構。利用磁光柯爾效應(Magnetic Optical Kerr Effect)進行一系列的磁性量測,此系統的磁滯曲線與一般恰好反相,即當磁場逐漸增加時磁性訊號翻轉方向與正常翻轉方式相反,查詢文獻後得知,此種反相磁滯曲線(Inverse hysteresis loop),可能源於鐵和鈀的界面在進行磁光柯爾效應量測時,產生負的柯爾訊號(Negative Kerr signal),而有反相磁滯曲線,並非鐵的磁性方向與外加磁場相反。另外我們發現,受到氫氣影響,垂直鎢表面方向上磁性增強,即(111)方向的頑性(coercivity)逐漸變大,且可透過適當熱處理將其消除,甚至最後磁易軸轉至平行於鎢表面。我們亦於皺化鎢表面鍍上不同量的鐵,當鐵的量較多時,剛開始磁易軸(Magnetic Easy Axis)將指向平行鎢表面,再受到氫氣影響,磁易軸最後亦轉至垂直方向,且居禮溫度(Curie Temperature)將較剛開始為高。最後,如在鎢表面鍍上鈀後,並未作退火處理即鍍上鐵,則無法觀察到殘氣對磁性結構的影響,然而只要經過退火處理,即使皺化金字塔較小,亦能觀察到明顯的殘氣影響。在熱脫附(Temperature programmed desorption)實驗中,由樣品脫附之氣體主要為氫氣,再降至低溫後,LEED圖形變為較清楚,然而此時即無法量到磁性,推測鐵可能和部分的鈀形成合金,因而鐵磁性消失。 Previous research have shown that, if we deposite more than 1 PML Pd on W (111), and treat it with proper annealing, the surface would reveal 10 nanometer scale 3-faced pyramids with {112} facets. With different annealing temperature, the size and uniformity of faceting pyramids would be different. In this experiment, we deposite iron on faceted Pd / W (111) surface to observe the effect of faceted surface to magnetic material. From LEED images, we know that iron cannot be orderly grown on faceted surface under room temperature, but we do not have the tools, such as STM, to observe the real morphology of iron on faceted surface. With a series of MOKE data, we observed that the hysteresis loops of this system are inversed. This inverse hysteresis loop has been discussed before. Some first principle calculations have shown that it is due to the negative Kerr signal from interface. We also found that the perpendicular magnetic anisotropy would be enhanced due to the hydrogen in the chamber. This effect can be eliminated by proper annealing, and further annealing would change the surface property. If we deposite more iron, the magnetization would be in in-plane direction in the beginning. The easy axis would change to perpendicular direction due to hydrogen effect. We also deposite iron on non-faceted Pd / W (111) surface. The hysteresis loops are inversed, but no coercivity enhancement effect is observed. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/27295 |
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顯示於系所單位: | 物理學系 |
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