鈷基合金薄膜之磁阻特性研究

Study of magnetoresistance characteristic of cobalt-based thin films

賴思宇(Ssu-Yu Lai)

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2007年)

摘要

本實驗利用直流與射頻磁控濺鍍法在二氧化矽基板上製備磁阻薄膜，實驗分為三個部分來探討薄膜特性：第一部份探討共濺鍍沈積Co-Ti-O單層顆粒合金薄膜；第二部分探討共濺鍍沈積Co-Hf-O單層顆粒合金薄膜；第三部分探討 [TiOx (10 nm)/Co (t nm)]10多層顆粒合金薄膜。
單層顆粒合金薄膜方面，主要是藉由改變Co的體積分率與熱處理溫度，藉以形成奈米尺寸的Co磁性金屬顆粒析出於TiOx或HfOx絕緣化合物基地上所組成的薄膜；而多層顆粒合金薄膜方面是藉由改變Co磁性金屬層的厚度，經不同溫度熱處理後，使Co顆粒在TiOx絕緣層中均勻析出，薄膜形成Co及TiOx之混合結晶相。實驗利用X光繞射儀(XRD)、穿透式電子顯微鏡(TEM)、振動試樣磁力計(VSM)、超導量子干涉磁化儀(SQUID)與四點探針(FPP)，觀察薄膜的微結構、相變化，並分析其電性、磁性質與磁阻特性之關係。
在Co-Ti-O單層顆粒合金薄膜，當Co原子百分比為84.72%經900C熱處理後在室溫下可得最大的磁阻率為2.72%。Co-Hf-O單層顆粒合金薄膜，當Co原子百分比為64.69%經900C熱處理後在室溫下可得最大的磁阻率1.22%。單層顆粒合金薄膜方面，隨著熱處理溫度的提高其磁阻率有增加的趨勢，其原因主要與磁性顆粒的析出、成長、分佈與顆粒間絕緣層的厚度有很大的關係。而[TiOx (10 nm)/Co (t nm)]10多層顆粒合金薄膜方面，Co層厚度分別為8、10、12 nm經500C熱處理後在室溫下可得最大的磁阻率分別為0.40%、0.49%、0.56%。在經高溫超過500C熱處理後會使Co、TiOx相互擴散，使多層膜的結構受到破壞而造成磁阻率下降。

並列摘要

Co-Ti-O granular/multilayers thin films and Co-Hf-O granular thin films were prepared using radio frequency and direct current magnetron co-sputtering on SiO2 substrate. Various Co concentrations of the granular thin films were annealed at a different elevated temperature to examine their properties. Post-annealed granular films had a nanoscale magnetic cobalt grains embedded in an immiscible insulator matrix. Multilayers thin films were investigated while varying the Co layer thickness. The studied film was annealed by a rapid thermal annealer (RTA) to yield Co-TiOx composite because annealing induced Co precipitate in TiOx matrix at an elevated temperature. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to detect the phase formation and crystal structure of the studied films. Magnetic property was measured using vibrating sample magnetometer (VSM) and surperconducting quantum interference devices (SQUID). MR effect was detected using a 4 - point probes under an applied magnetic field of -2kOe to 2kOe.

The maximum MR of 2.72% and 1.22% were found for the Co-Ti-O (84.72%) and Co-Hf-O (64.69%) granular thin films at room temperature, respectively. The MR effect of granular films increased with increasing annealed temperature, and showing that depended strongly on the Co concentration, grain sizes and the thickness of the insulator between metallic grains. [TiOx (10 nm)/Co (t nm)]10 multilayers had MR of 0.40%, 0.49% and 0.56% at room temperature when the thickness of Co were 8, 10 and 12 nm, respectively. The multilayer structure was eliminated when the film was annealed at 500C and above, suggesting that the interdiffusion had occurred between the layers, hence, the MR of the films fell.

參考文獻

[11] G.N. Kakazei, Yu.G. Pogorelov, A.M.L. Lopes, M.A.S. da Silva, J.A.M. Santos, J.B. Sousa, S. Cardoso, P.P. Freitas, E. Snoeck, J. Magn. Magn. Mater. 266 (2003) 62.

[47] J. H. Hsu, Y. H. Huang, P. K. Tseng, D. E Chen, IEEE Trans. Magn. 34 (1998) 909.

[40] Yu. E. Kalinin, M. N. Kopitin, S.A.Samsonov, A. V. Sitnikov, O.V. Stognei, Taylor ＆ Francis 307 (2004) 243.

[22] J. Q. Xiao, J. S. Jiang and C. L. Chien, Phys. Rev. Lett. l.68 (1992) 3749.

[23] J. Q. Xiao, J. S. Jiang and C. L. Chien, Phys. Rev. Lett. 68 (1992) 3749.