銀覆蓋層在鈷-鉑(111)超薄膜上的研究

The Study of Capping Layers of Ag on Co/Pt (111) ultrathin films

吳月娥(Yue-E Wu)

指導教授 ： 沈青嵩

國立臺灣師範大學/理學院/物理學系/博士(2001年)

摘要

摘要摘要本論文的主題是以歐傑電子能譜術、低能量電子繞射、紫外光電子能譜術以及磁光柯爾效應來研究銀、鈷超薄膜長在鉑 (111) 表面上的成長模式、結構、合金形成和磁性。這些磁性包括居禮溫度、矯頑力、磁異向性和自旋反轉，而且這些磁性和薄膜成長條件、薄膜厚度、覆蓋層或緩衝層的加入與否、退火過程等都有很密切的關係。鈷超薄膜長在鉑 (111) 表面是屬於 SK的成長模式。當薄膜厚度小於四層時，它的易軸方向垂直於薄膜表面；厚度越厚時易軸方向就轉成為平行於薄膜表面。一層的鈷/鉑 (111) 樣品經過710 K 的退火效應後，其垂直柯爾訊號有很明顯的增強現象。在鈷-鉑 (111) 系統中，鈷的厚度越厚時樣品的居禮溫度越高。鈷長在平坦的鉑 (111) 表面，其矯頑力隨鈷厚度的增加而減小；當鈷長在粗糙的鉑 (111) 表面時，其矯頑力卻不受鈷厚度的影響。銀鍍在薄的鈷-鉑 (111) 表面時，銀會抑制鈷的自旋反轉；當銀鍍在厚的鈷-鉑 (111) 表面時，銀會使樣品的易軸方向由平行於薄膜表面轉成為垂直於薄膜表面。這種SRT的現象，主要是由於銀覆蓋層的加入使得樣品的表面磁異向性常數增加的原因。鈷-鉑形成合金的過程中，銀一直保持在樣品的最上層。銀覆蓋層對樣品的垂直磁異向性有很重要的影響，它也會增加鈷-鉑 (111) 系統的居禮溫度。在鈷-銀-鉑 (111) 系統中，當溫度夠高時銀會浮到樣品的最上層，而這種鈷和銀原子的交換也會影響鈷-鉑合金的形成。鈷、銀原子開始交換的溫度不受銀厚度的影響，而交換完成的溫度隨銀厚度的改變而改變。 Abstract Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), ultraviolet photoelectron spectroscopy (UPS), and magneto-optical Kerr effect (MOKE) were used to study the growth mode, structure, alloy formation, and magnetic properties of Ag, Co ultrathin film on Pt (111) surface. The magnetic properties, such as Curie temperature (Tc), coercivity (Hc), magnetic anisotropy (MA), and spin reorientation transition (SRT) of the magnetic ultrathin films are significant influenced by the growth conditions, film thickness, addition of capping layer or buffer layer, and annealing process. The growth of Co ultrathin film on Pt (111) is Stranski-Krastanov mode. The easy axis of magnetization is oriented perpendicular to the film plane as Co film thickness less than 4 ML, and changes into in-plane for thick film. A giant enhancement in the polar Kerr signals is observed after annealing 1 ML Co/Pt (111) at 710 K. The Curie temperature increases as Co thickness increases. The coercivity decreases as the Co coverage increases for the flat Pt (111) surface, but is independent of Co thickness for the sputtered one. The sitting of Ag atoms on the top of thin Co/Pt (111) film prevents the spin reversal of Co, and it changes the easy axis of magnetization from in-plane to out-of-plane for thick Co/Pt (111) film. The increasing of the surface anisotropy after Ag atom deposition may be the main mechanism that causes the representation of SRT. Ag atoms always stay on the topmost layer during the Co-Pt alloy formation. Ag capping layers have an important contribution in the perpendicular magnetic anisotropy (PMA). The Curie temperature increases after Ag overlayer deposition on Co/Pt (111) surface. The exchange between Co and Ag atoms affects the formation of Co-Pt alloy. Ag atoms float to the top layers when annealing temperature is high enough. The starting exchange temperature is independent of Ag coverage, but the complete exchange temperature depends on the Ag film thickness.

關鍵字

歐傑電子能譜術 ； 鐵磁性物質 ； 有效磁異向性常數 ； ( 表面)磁光柯爾效應 ； 垂直磁異向性 ； 矯頑力 ； 居禮溫度 ； 自旋反轉

並列摘要

Auger electron spectroscopy (AES), low-energy electron diffraction (LEED),
ultraviolet photoelectron spectroscopy (UPS), and magneto-optical Kerr effect (
MOKE) were used to study the growth mode, structure, alloy formation, and
magnetic properties of Ag, Co ultrathin film on Pt (111) surface. The magnetic
properties, such as Curie temperature (Tc), coercivity (Hc), magnetic
anisotropy (MA), and spin reorientation transition (SRT) of the magnetic
ultrathin films are significant influenced by the growth conditions, film
thickness, addition of capping layer or buffer layer, and annealing process.
The growth of Co ultrathin film on Pt (111) is Stranski-Krastanov mode. The
easy axis of magnetization is oriented perpendicular to the film plane as Co
film thickness less than 4 ML, and changes into in-plane for thick film. A
giant enhancement in the polar Kerr signals is observed after annealing 1 ML
Co/Pt (111) at 710 K. The Curie temperature increases as Co thickness
increases. The coercivity decreases as the Co coverage increases for the flat
Pt (111) surface, but is independent of Co thickness for the sputtered one.
The sitting of Ag atoms on the top of thin Co/Pt (111) film prevents the spin
reversal of Co, and it changes the easy axis of magnetization from in-plane to
out-of-plane for thick Co/Pt (111) film. The increasing of the surface
anisotropy after Ag atom deposition may be the main mechanism that causes the
representation of SRT. Ag atoms always stay on the topmost layer during the Co-
Pt alloy formation. Ag capping layers have an important contribution in the
perpendicular magnetic anisotropy (PMA). The Curie temperature increases after
Ag overlayer deposition on Co/Pt (111) surface.
The exchange between Co and Ag atoms affects the formation of Co-Pt alloy. Ag
atoms float to the top layers when annealing temperature is high enough. The
starting exchange temperature is independent of Ag coverage, but the complete
exchange temperature depends on the Ag film thickness.