(鐵鉑或鈷鐵)與鋨之多層膜的結構與物性研究

STRUCTURE AND PROPERTY STUDIES OF [(FePt or CoFe)/Os]n MULTILAYER FILMS

蔣大鵬(Da-Pun Chiang)

指導教授 ： 林鴻明 ； 姚永德

大同大學/工程學院/材料工程學系所/博士(2011年)

摘要

本論文主要是將具高矯頑磁場適合做磁記錄媒體材料的鐵鉑合金，及具高飽合磁化強度適合做磁頭材料的鈷鐵合金；以鋨(Os)為中間層，並限制磁性層的總厚度控制在100 nm後，製作出二系列多層膜[FM (x)/Os(1)]n，然後研究其結構與物性之變化。上式中：x表示單層鐵磁性層(FM)的厚度，單位為nm；n表示層數；且nx乘積為100。以X光繞射儀(XRD)做晶相與結構分析、振動樣品磁化儀(VSM)做磁性分析、原子力顯微鏡(AFM)做表面型態分析和高解析穿透式電子顯微鏡(HRTEM)做內部結構分析。針對鐵鉑合金，由熱處理溫度對[FePt(x)/Os(1)]n，n=20,50層之結構及磁性變化，發現鐵鉑合金之層數會影響結構之序化參數；亦即層數增加後需要較高的熱處理溫度才能形成L10 FePt相，亦即才能提升其矯頑磁場。例如，在膜層為50層時序化參數較小，需要超過800oC以上，矯頑磁場才會有較明顯提升。對鈷鐵合金而言，[CoFe(x)/Os]n，n≧50時，在2θ為36o~50o的寬帶間有(110)CoFe相形成。未熱處理之n= 50樣品為無序bcc結構的 (110)CoFe相，但經500oC熱處理後，會逐漸轉變為有序bct結構。經由多層膜的堆疊，在n= 100時，可直接形成有序bct結構的(110)CoFe相。原子力顯微鏡觀察樣品的表面平滑度，發現隨著層數增加表面更顯平整。高解析的穿透式電子顯微鏡觀察[CoFe(x)/Os(1)]n的內部結構，底下膜層界面較為平整，往上則逐漸具波浪狀。在磁性研究方面，發現多層CoFe薄膜，在較大膜厚時，具有多磁區的特性，而在膜層厚度減少，會出現單磁區及超微粒子的特性，當有超順磁效應出現，會使矯頑磁場快速減少。

關鍵字

超順磁 ； 單磁區 ； 多磁區 ； 矯頑磁場 ； 序化參數 ； 多層膜

並列摘要

Microstructure and magnetic properties of multilayer [FePt(x)/Os]n and [CoFe(x)/Os(1)]n films by dc-magnetron sputtering (with x being thickness in nm; Os with a fixed thickness 1 nm; n being the number of layers and nx is fixed to 100) have been studied. Os layers were used to control the ordering of and the grain size of magnetic layers by its thickness. For FePt series, the [FePt(x)/Os(1)]n films with n=20 and 50 were annealing between 300 and 900 oC, the ordering parameter decreases with increasing the number of Os layers. The coercive force (Hc) as a function of the annealing temperature for pure FePt behaves roughly saturated after annealing above 700 oC. However, for samples with n = 20 and 50, the value of Hc is still low with annealing temperature at 800 oC, This means forming L10 FePt requires to increase annealing temperature after increasing Os layers. Our experimental results are reasonably well to describe the effect of strain-assisted transformation. For CoFe series, the XRD patterns of all the samples have demonstrated that the CoFe(110) phases can be induced in samples with x small than 2 nm by the texture effect between Os and CoFe layers. The texture growth of disordered (110)bcc CoFe phase in sample with x = 2 nm and the ordered (110)bct phase in sample with x = 1 nm. After annealing at 500 oC, the XRD peak for sample with x = 1 nm is unchanged, however, for sample with x = 2nm, the bcc (110) peak is gradually split into two: one corresponding to the ordered bct phase, and the other, to the disordered bcc phase. The surface roughness for sample with n = 100 is much smaller than all other samples. From the magnetic studies, the variation among the multi-domain, single domain, and super-paramagnetism is demonstrated for samples with x varied from 100 to 1 nm. Finally, the Os layers can be a good candidate to control the texture, grain growth and the inter diffusion among magnetic layers.

並列關鍵字

single domain ； multi-domain ； coercive force ； ordering parameter ； multilayer ； super-paramagnetism

參考文獻

113. 賴育誠，國立成功大學材料科學及工程學系，博士論文，2007.06

162. 陳士元, 清華大學材料科學工程學系, 博士論文, (2010)

174. 蘇泰廷，國立清華大學材料科學工程學系，碩士論文, (2011)

119. Halliday, Resnick, Walker, Wiley International Edition, “Fundamentals of physics”, 7th ., ch40, p.1112~1118, (2005)

179. N.D. Ha, T.S. Yoon, H.B. Kim, J.J. Lim, C.G. Kim, C.O. Kim, Journal of Magnetism and Magnetic Materials 290–291, 1571–1575,(2005)