退火過程中磊晶Fe/Pt多層膜轉變為序化FePt薄膜之結構與磁性變化研究

The Study of the Structural and Magnetic Transition from Epitaxial Fe/Pt Multilayers to Ordered FePt Thin Films under Annealing

陳佑昇(Yu-Sheng Chen)

指導教授 ： 李志浩

國立清華大學/原子科學院/工程與系統科學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00584

摘要

成功利用離子束濺鍍系統成長出成分比例接近1:1的磊晶非序化Fe/Pt多層膜，而此多層膜隨退火溫度增加轉變為磊晶序化FePt合金薄膜的過程中結構與磁性變化是本研究的重點。
從結構上得知退火500 °C為溫度轉換點，此時Fe/Pt多層膜結構開始被破壞，當退火溫度達700 °C時，形成(001)方向磊晶的L10序化FePt合金薄膜，序化度達0.95以上。除此之外，從不同退火溫度的c/a比值皆小於0.98得知退火過程中只牽涉Fe和Pt原子的交互擴散並沒有造成太大的晶格變形。
從磁性來看，當退火溫度達700 °C，序化度與垂直向的方正性接近1，磁晶異向常數增大至約3×107 erg/cc，表示具有明顯的PMA性質。此外，Hc在退火溫度600 °C時有最大值約1960 Oe，當達700 °C則Hc下降至1300 Oe左右。
對於垂直向的morb/mspin比值來說，未退火的Fe/Pt多層膜約0.088；500 °C退火約0.149；經過700 °C退火形成序化FePt合金薄膜後約0.174，大致上可看出序化度越高，Fe和Pt之間的軌域混層越強，再加上自旋-軌道耦合越大，軌道磁矩的異向性越明顯，使得測量所得之垂直向的morb/mspin比值越大。

關鍵字

垂直異向性 ； Fe/Pt多層膜 ； 離子束濺鍍 ； 單晶繞射 ； X光磁性圓二相色性

並列摘要

An epitaxial L10 Fe/Pt thin film grown from the Fe/Pt multilayer with a composition of almost 1:1 was prepared successfully using ion beam sputtering deposition. To study the structural and magnetic transition from an Fe/Pt multilayer to an epitaxial FePt alloy thin film is the key point in this research.
The Fe/Pt multilayer was grown at 100 °C and the multilayer structure was destroyed at an annealing temperature of 500 °C. When the annealing temperature reached 700 °C, the L10 ordered FePt film with growing along (001) orientation epitaxially was obtained. The order parameter reached above 0.95. In addition, c/a ratios of FePt films annealing at different temperatures were below 0.98. This result implies that the interdiffusion of Fe and Pt atoms during the annealing did not distorted the lattice structure too much.
After the sample was annealed at 700 °C, the out-of-plane order parameter and squareness were close to 1 and magnetocrystalline anisotropy constant reached 3×107 erg/cc. It was indicated that the ordered FePt film has strong PMA effect. The ordered FePt film exhibited an out-of-plane coercivity of 1960 Oe after annealing at 600 °C, but it decreased to 1300 Oe after annealing at 700 °C.
For the out-of-plane spin-to-orbital ratio, the Fe/Pt multilayer without annealing was 0.088; the Fe/Pt multilayer after annealing at 500 °C was 0.149; and the ordered FePt film after 700 °C was 0.174. It can be inferred that the higher order parameter, the stronger hybridization and spin-orbital coupling between Fe and Pt atoms occurs. Also, the higher orbital magnetic moment anisotropy implies the out-of-plane spin-to-orbital ratio becomes larger.

並列關鍵字

PMA ； Fe/Pt multilayer ； ion beam sputtering ； XRD for single-crystal analysis ； MCD

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