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標題: 磁性薄膜之鐵磁共振特性測量
Studying Ferromagnetic Resonance Properties of Magnetic Thin Films
作者: 陳煜仁
Chen, Yu-Jen
關鍵字: Ni80Fe20
ferromagnetic resonance
出版社: 奈米科學研究所
摘要: 本研究主要探討鎳鐵薄膜的鐵磁共振特性,測量方法包含了穿透式及反射式量測,同時搭配上實驗室自製的超高感度微波向量偵測器,可精確測量出鐵磁共振效應對微波訊號的影響。穿透式量測在共平面波導(CPW)的架構下進行研究, 樣品中央波導帶(signal path)是由長3.6 mm、寬50 um、厚100 nm的鎳鐵薄膜構成通道,兩旁接地(ground)則是100 nm黃金薄膜。另一種方式是反射式量測,其擁有不需要圖案化及非破壞性量測兩項優點,不但節省品製作時間,也能大量快速的測量樣品微波特性。 量測結果發現,磁場射入角度越平行樣品時,鐵磁共振磁場減小、零場附近的磁阻相對於磁場變化較靈敏,而當磁場平行樣品射入時,鐵磁共振磁場峰值及寬度會隨著量測頻率增加而增大,若將其量測結果進一步分析可推算出: 幾何形狀引起的各方向去磁因子Nx、Ny、Nz (Demagnetizing factor),以及阻尼進動的阻尼因數α(Gilbert damping parameter)。由CPW樣品所算出: Nx = 0.13 ± 0.02、Ny = 0.75 ± 0.08、Nz = 0.12 ± 0.02、α= 0.053,反射式量測鎳鐵薄膜:Nx = 0 ± 0.17、Ny = 1 ± 0.34、Nz = 0 ± 0.17、α= 0.04。另外,我們也利用反射式系統量測Spin-valve樣品,發現亦可以在未圖案化情形下量測出磁阻變化。
In this study, we use two methods to detect ferromagnetic resonance (FMR) properties of the Permalloy (Ni80Fe20) thin film: transmission and the reflectometry. The precise variations of microwave signals through the sample were measured by a home-made ultra-high sensitivity microwave vector meter. The transmission measurement system is based on a coplanar waveguide (CPW) which contains a signal path made of Permalloy (3.6 mm long, 50 um wide, 100 nm thick) and ground pads consisted of 100-nm-thick gold film. In the reflectometry measurement setup, we do not need to pattern the magnetic thin film and it is a non-destructive detection method. Our results show that magnetoresistances decrease more rapidly near zero field and the resonant magnetic field of FMR shifts to the lower field when the angle between the surface of sample and the direction of the magnetic field decreases. The resonant magnetic field of FMR moves to the higher field and the shape of ferromagnetic resonances becomes broader when the microwave signal frequency increases. From the measurement results, we are able to deduce demagnetization factors (Nx, Ny, Nz) and damping parameter (α). The calculation results of the CPW sample are Nx = 0.13 ± 0.02、Ny = 0.75 ± 0.08、Nz = 0.12 ± 0.02、α= 0.053; of reflectometry measurements of Permalloy thin film are Nx = 0 ± 0.17、Ny = 1 ± 0.34、Nz = 0 ± 0.17、α= 0.04. Apart from the permalloy samples, we also use reflectometer to detect a spin-valve sample. We successfully determine the magnetoresistance variation of an unpatterned thin film.
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