鐵/鉑(111)超薄膜上曝氧之組成與磁性研究

Investigation of compositions and magnetic properties for ultrathin Fe/Pt(111) films after oxygen exposure

李盈蓁

指導教授 ： 蔡志申 ； 何慧瑩

國立臺灣師範大學/理學院/物理學系/碩士(2009年)

摘要

我們利用歐傑電子能譜儀(AES)及表面磁光柯爾效應儀(SMOKE)探測鐵超薄膜在純白金上經曝氧後的成分及磁性變化。在室溫下對鐵/鉑(111)系統曝氧，樣品表面含氧量隨著曝氧量增加而變大，當樣品表面含氧量達到飽和之後，表面含氧量即不再變化。從曝氧量的分析得知，平整的鐵薄膜表面較易形成鐵氧的化合，當表面形成氧化鐵之後，會開始出現島狀結構使表面變得不平坦，此時氧原子進行物理吸附速度會加快。不同厚度的鐵/鉑(111)樣品曝氧後，磁化易軸與未曝氧的系統一樣皆為縱向，然而受到表面形成之氧化鐵為弱鐵磁性所影響，表面曝氧達飽和吸附後，柯爾訊號會變弱。分析熱退火對曝氧前後之2 ML、3 ML鐵/鉑(111)系統的矯頑場之影響，我們發現無論是曝氧前或曝氧後的系統，其矯頑場在退火之後皆會上升，但是曝氧後的樣品矯頑場在較低的退火溫度即開始上升，可能是因為表面形成之氧化鐵具有鍵能較強的離子鍵，使得鐵原子不易向鉑基底擴散，因此能和鉑形成合金的純鐵厚度減少，使混合溫度提前。另外，鐵鉑合金會使矯頑場上升，然而表面氧化鐵形成會造成樣品的居禮溫度下降，此兩現象相互競爭，結果使矯頑場的變化並非隨著溫度升高而持續上升。從運用於磁記錄體的觀點出發來看，表面氧化鐵的形成對鐵鉑合金系統而言，因為不利於矯頑場增進的現象，因此較沒有實用的價值。

關鍵字

表面磁光柯爾效應儀 ； 鉑(111) ； 鐵 ； 曝氧 ； 歐傑電子能譜儀

並列摘要

Auger electron spectroscopy (AES) and surface magneto-optical Kerr effect (SMOKE) were used to investigate compositions and magnetic properties of ultrathin Fe/Pt (111) films after oxygen exposure. We exposed oxygen onto the Fe/Pt(111) surface at room temperature. The concentration of surface oxygen increases with oxygen exposure until reaching a saturated value. When the iron becomes iron oxides on the surface, the surface becomes rough. This makes an increase of physical absorption of oxygen atoms on the surface. The magnetic easy axes are in the in-plane direction before and after oxygen exposure. The Kerr intensity at saturated condition decreases because of the weakly ferromagnetic properties of the iron oxides. The longitudinal coercivity of O2/2~3 ML Fe/Pt(111) raised after annealing both before and after oxygen exposure. The starting temperature of enhancing coercive force of O2/Fe/Pt(111) is lower than that before oxygen exposure. This may due to the strong ion bond of iron oxides. The ion bond between iron and oxygen atoms makes it more difficult for iron atoms to diffuse toward the Pt substrate. From this point of view, the thickness of pure iron on platinum surface decreased and this makes the decrease in the temperature of the Fe-Pt alloy formation. The coercive force increases when the iron and platinum form Fe-Pt alloy, meanwhile the formation of iron oxides will decrease the Curie temperature of the sample. Due to the competition of these two effects, the longitudinal coercivity of O2/2~3 ML Fe/Pt(111) does not continue to ascend with the annealing temperature. From this point of view, the formation of iron oxides is unfavorable for the application of Fe-Pt alloy on ultra-high density magnetic storage media.

參考文獻

[1] H. Le Gall, R. Sbiaa and S. Pogossian, J. Alloys Comp. 275-277, 677 (1998)

[4] Herman J. Borg and Roel van Woudenberg, J. Magn. Magn. Mater.193, 519 (1999)

[5] Pei-Yih Liu and Han-Ping D. Shieh, J. Magn. Magn. Mater. 155, 385 (1996)

[6] Y. Murakami, A. Takahashi, S. Terashima, J. Phys .Chem .Sol 56, 1535 (1995)

[9] W. B. Zeper and F. J. A. M. Greidanus, J. Appl. Phys., 65, 497 (1989).