磁性薄膜之表面形貌與磁性行為

Abstract

本論文主要探討磁性膜薄的表面形貌與磁性行為之間的關係。實驗架構總共可分成三部分：(1)高定向熱解石墨基板系統(2)三氧化二鋁(藍寶石基板)系統(3)矽(111)基板系統。 高定向熱解石墨基板系統中，利用氬離子轟擊基板，造成基板表面形成缺陷，藉由掃描穿隧式電子顯微鏡觀察鈷原子在平坦的高定性熱解石墨基板上的表面形貌，鈷原子成核的尺寸較表面缺陷的高定性熱解石墨基板上來的大，換句話說，鈷原子成核分佈在表面缺陷的基板上的密度較高。由歐傑電子能譜儀的分析結果可以間接顯示出基板的表面缺陷會使鈷原子成核分佈的更均勻。在磁性方面，利用平行與垂直方向的磁光科爾效應來觀察兩種不同基板的磁性行為。在平坦的基板，鈷薄膜的易軸為平行磁化方向；特別的是，在表面缺陷的基板，鈷薄膜在水平與垂直方向皆可量測到柯爾訊號。經過測試發現易軸為斜向的磁化方向，在厚度達到60ML時仍可以測得。 三氧化二鋁(0001)系統中，利用斜角鍍磁性薄膜(鐵)的方式，造成單軸的磁異向能產生，藉由掃描穿隧式電子顯微鏡觀察在鍍膜角度為0°時，表層鈀原子成核形狀具有三重對稱性；在鍍膜角度為45°與65°時，鈀表面由數奈米大小的顆粒組成。在磁性方面，鍍膜角度為0°時，各個方向角(∅)所量測到的磁滯曲線都是呈現方形的形狀；在鍍膜角度為45°與65°時，產生單軸的磁異向性，易軸方向：沿著方位角∅=0°；難軸方向：沿著方位角∅=90°。 矽(111)基板系統中，我們再一次做了斜角鍍磁性薄膜的實驗，結果與在藍寶石基板中的結果相符。透過改變不同的合金介面層材料(鐵、鎳、鈀)，可以觀察到不同的磁性行為，鐵薄膜在鐵-矽合金介面上的矯頑磁力(Hc=130 Oe)大於在鈀-矽合金介面(Hc=50 Oe)與鐵/矽(111)(Hc=50 Oe)。

We studied the correlation between surface morphology and magnetic behavior of magnetic thin films.The experiment was divided into three parts. (1) HOPG system. (2) Al2O3(0001) system,and (3) Si(111) system. In HOPG system, we used Ar+ sputtering to create surface defects. Co atom nucleation size in planar-HOPG was larger than in sputtered-HOPG. In planar-HOPG, Co films prefer a magnetizeation direction. In the surface plane, In Co/sputteredp-HOPG, we measured Kerr hysteresis loops in both the polar and longitudinal directions. The easy axis is confirmed in an oblique direction, even at the Co thickness of 60 ML. In Al2O3(0001) system, we used oblique deposition to induce an uniaxial MAE in Fe films. For 0°-Fe/Al2O3(0001), the Pd capping layer can still preserve the 3-fold symmetry. However, in Pd/45°-Fe/Al2O3(0001) and Pd/65°-Fe/Al2O3(0001), the Pd capping layers were composed of nanoclusters. For Pd/0°-Fe/Al2O3(0001), the hystersis loops were always of a square shape, which is invariant with the azimuthal measurement angle ∅.For Pd/45°-Fe/Al2O3(0001) and Pd/65°-Fe/Al2O3(0001), an uniaxial anisotropic magnetic behavior was observed. The easy axis is along the ∅=0 deg and The hard axis is along the ∅=90 deg. In Si(111) system, we masured obliquely depositied films again.The results are consistant with the Al2O3(0001) system. By choosing different alloy interface materials(Fe、Pd、Ni), we can see different magnetic behavior. The coercivity field(Hc) of Fe/Fe-silicide/Si(111)(Hc=130 Oe) was much larger than Fe/Pd-silicide/Si(111)(Hc=50 Oe) and Fe/Si(111)(Hc=50 Oe).