基於網路分析儀之鐵磁共振儀的建製及磁性多層膜高頻共振性質研究
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2010
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Ruderman-Kittel-Kasuya-Yoshida (RKKY) 等磁層耦合現象在巨磁阻效應(GMR)之中扮演了重要的角色，而這個現象的發現奠定了近代自旋電子學的發展。當系統的自由能己知，用來描述自旋電子動力學的Landau-Lifshitz-Gilbert方程可得到許多關於此系統的訊息。例如：耦合系數﹑阻尼系數﹑鬆弛時間,晶格場以及磁異向係數等等。了解這些係數，不但可以幫助我們探究其原理更可以獲得操控自旋電子，發展自旋電子技術更多的靈感。
鐵磁共振技術在量測這些參數上，是強而有力的工具。 為了研究 Py/Ru/Py 磁性三層膜，我們使用了向量網路分析儀建製了一套鐵磁共振儀。由於向量網路分析儀的特性以及在 X-band下高Q值的共振腔，不需使用傳統鐵磁共振儀的調變相鎖放大技巧來獲得高敏感度。可以直接量測鐵磁共振吸收利用數值方法得到吸收的微分。若需要作別的微波波段的量測，也只需更換共振腔，不需改變硬體配置。
為了成長所需樣品，我們建造了一套具有四支磁控濺鍍槍的超高真空濺鍍系統。此系統具有穩定而低的鍍率，是故樣品的膜厚可達到原子的尺度。我們也翻新了一台振動樣品磁量儀用以量測樣品的飽和磁化，這個性質我們無法藉由鐵磁共振的結果來獲得。
我們備製了一系列的 Py20nm/Rut/Py20nm 樣品 t 的範圍從0.4nm 到 3nm。角度解析的鐵磁共振資料顯示了三層膜的RKKY磁層耦合現象，耦合常數隨著膜厚成振盪的變化。這樣的結果也可以由磁阻量測以及振動樣品磁量儀的結果獲得印證。
Magnetic couplings, such as RKKY, plays key role on GMR that establishes the area of spintronics since its discovery. Spin dynamics governed by LLG equation tells a lot of information about the magnetic system once its free energy density is known. For examples, the exchange coupling, damping constant, relaxation time, internal field, anisotropic coefficients, etc. Knowledge of these parameters help us not only the deep insight into the nature, but also the manipulation of spin engineering. Ferromagnetic resonance (FMR) is a very powerful technique to indentify these parameters. In order to study the magnetic coupling of Py/Ru/Py magnetic trilayer, a vector network analyzer VNA-FMR spectrometer was developed. Since benefits gain from the state-of-the-art VNA and high Q cavity at X-band, lock-in field modulation technique is no longer necessary as that used in conventional FMR spectrometer. FMR absorption spectrum can be extracted directly, which would be post-derivative for further analysis without altering the original behavior. Furthermore with this assembly, microwave cavity other than X- band could also be used without changing any hardware. An UHV sputtering system with four 2” magnetron-sputtering guns was also constructed for sample fabrication. Due to the stable and low deposition rate, sample thickness at atomic regime can be made. A VSM was also refurbished to determine the saturation magnetization of sample which should be known somehow, but can not be obtained from FMR. A series of Py(20nm)/Ru(t)/Py(20nm) was made with t ranged from 0.4 to 3nm. The angular FMR data shows RKKY coupling. And the result is in good agreement with VSM and MR result.
Magnetic couplings, such as RKKY, plays key role on GMR that establishes the area of spintronics since its discovery. Spin dynamics governed by LLG equation tells a lot of information about the magnetic system once its free energy density is known. For examples, the exchange coupling, damping constant, relaxation time, internal field, anisotropic coefficients, etc. Knowledge of these parameters help us not only the deep insight into the nature, but also the manipulation of spin engineering. Ferromagnetic resonance (FMR) is a very powerful technique to indentify these parameters. In order to study the magnetic coupling of Py/Ru/Py magnetic trilayer, a vector network analyzer VNA-FMR spectrometer was developed. Since benefits gain from the state-of-the-art VNA and high Q cavity at X-band, lock-in field modulation technique is no longer necessary as that used in conventional FMR spectrometer. FMR absorption spectrum can be extracted directly, which would be post-derivative for further analysis without altering the original behavior. Furthermore with this assembly, microwave cavity other than X- band could also be used without changing any hardware. An UHV sputtering system with four 2” magnetron-sputtering guns was also constructed for sample fabrication. Due to the stable and low deposition rate, sample thickness at atomic regime can be made. A VSM was also refurbished to determine the saturation magnetization of sample which should be known somehow, but can not be obtained from FMR. A series of Py(20nm)/Ru(t)/Py(20nm) was made with t ranged from 0.4 to 3nm. The angular FMR data shows RKKY coupling. And the result is in good agreement with VSM and MR result.
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Keywords
磁性多層膜, 鐵磁共振, Magnetic multilayer, FMR, Ferromagnetic resonance