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標題: | 研究磊晶與多晶結構釔鐵榴石磁性絕緣體中純自旋電流的產生 Investigation of the pure spin current generation in epitaxial and poly-crystal magnetic insulator YIG |
作者: | Feng-Jen Chang 張逢仁 |
指導教授: | 黃斯衍(Ssu-Yen Huang) |
關鍵字: | 自旋電子學,熱自旋電子學,純自旋電流,自旋幫浦,自旋塞貝克效應,釔鐵榴石,晶體結構, spintronics,spin-caloritronics,pure spin current,spin pumping,spin Seebeck effect,yttrium iron garnet,crystal structure, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 我們透過使用不同的濺鍍基板,製造出磊晶或多晶結構的釔鐵榴石(Yttrium iron garnet, Y3Fe5O12)薄膜,來研究其晶體結構對於由自旋幫浦(spin pumping)效應以及由自旋塞貝克效應(spin Seebeck effect)所產生之自旋電流的影響。透過研究在鄰接之白金薄膜中所產生的逆自旋霍爾效應(inverse spin Hall effect)電壓,我們觀察到由自旋幫浦所產生的自旋電流,在多晶薄膜中比在磊晶薄膜中小了兩個數量級,但由自旋塞貝克效應所產生的自旋電流,與薄膜的晶體結構並沒有太大關係。我們分析,在多晶薄膜中由自旋幫浦所產生的自旋電流,是被這些薄膜中較大的磁阻尼係數(damping constant)抑制。我們發現多晶薄膜的磁阻尼係數,比磊晶薄膜的磁阻尼係數大了一個數量級。由這個分析結果,我們認為釔鐵榴石的磁阻尼係數,對於自旋幫浦以及自旋塞貝克效應有不同的影響。
磁阻尼係數對自旋幫浦以及自旋塞貝克效應的不同影響,揭示了這兩個效應當中,產生自旋電流之機制的不同。自旋幫浦仰賴釔鐵榴石中磁矩的同調性(coherent)運動來產生自旋電流,而自旋塞貝克效應則是透過磁矩的非同調性(non-coherent)運動來產生自旋電流。因此,自旋幫浦會顯著地被過大的磁阻尼係數抑制,但自旋塞貝克效應卻並不受影響。我們的結果不僅突顯出自旋幫浦和自旋塞貝克效應擁有不同的機制,也揭示了多晶性釔鐵榴石薄膜的應用潛力。因為多晶性釔鐵榴石薄膜可以成長在常用的基板上,例如矽基板,所以它更適用於製造運用純自旋電流原理的自旋電子學或熱自旋電子學元件。另外,由於自旋塞貝克效應具有不受晶體結構影響的特性,我們認為它應是在研究逆自旋霍爾效應時的較佳工具。 Yttrium iron garnet (YIG, Y3Fe5O12) thin films with the epitaxial and the poly-crystal structures were grown by sputtering on different substrates to investigate the influence of their crystal structure on the spin current generation and detection by the spin pumping and spin Seebeck effect (SSE). By investigating the inverse spin Hall effect (ISHE) voltage in an adjacent Pt layer, we observed that the spin current generated by the spin pumping in the poly-crystal films were two-order-of-magnitude smaller than that in the epitaxial film, while the spin currents generated by the SSE were irrelevant to the crystallinity of YIG. We demonstrated that the suppression of spin pumping in the poly-crystal YIG films was due to their large damping constants, which arose from the grain structures. The damping constants of the poly-crystal YIG films were one-order-of magnitude larger than that of the epitaxial film. Thus, we concluded that spin pumping and SSE had different dependence on the damping property of YIG. The reason behind this difference indicates that the spin-current-generation by spin pumping and SSE has different mechanisms. Spin pumping relies on the coherent motions of the magnetic moments in YIG to generate the spin current, while SSE generates the spin current by the non-coherent motions of them. Consequently, spin pumping is significantly suppressed by the large damping constant of the poly-crystal YIG, while SSE is not sensitive to it. Our results highlight not only the different mechanism of the spin pumping and SSE, but also the application potential of the poly-crystal YIG films. Since the poly-crystal YIG film can be grown on the commonly used substrates, such as silicon, it will be more feasible for the fabrication of the spintronics and spin-caloritronics devices based on pure spin current physics. Moreover, due to the unique property of SSE with insensitivity to the crystal structure, it should be a better tool to study ISHE phenomenon. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/50548 |
DOI: | 10.6342/NTU201601281 |
全文授權: | 有償授權 |
顯示於系所單位: | 物理學系 |
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