鎳鐵合金/釓雙層結構之自旋轉矩鐵磁共振
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2023
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Abstract
稀土金屬釓(Gadolinium, Gd)的目前被認為具有強自旋軌道耦合(Spin orbital coupling, SOC)是具有自旋流(Spin current)現象的材料，且在低 於室溫的居里溫度，會從順磁性轉變到鐵磁性。因此本研究利用電子束蒸 鍍製作了鎳鐵合金(Ni80Fe20, Permalloy, Py)及釓(Gadolinium, Gd)雙層 結構，並觀測自旋轉矩鐵磁共振(Spin-torque ferromagnetic resonance, ST- FMR)現象來探討自旋流造成的自旋軌道轉矩(Spin orbit torque, SOT)貢 獻，最終透過分析找出代表 Gd 自旋-電荷的轉換效率(Spin-charge conversion efficiency)的自旋霍爾角(Spin Hall angle, 𝜃SH)。接著也將此雙層結構在低溫中進行變溫 ST-FMR 測量，並藉由分析飽 和磁化強度(Saturationmagnetization, 𝑀S)及𝜃SH探討低溫下對於溫度的依 賴性並觀察在 Gd 臨界溫度下的磁性相變的影響。此外在 80K 以下 ST-FMR 數據出現一些變化，對於 SOT 及𝜃SH有顯著的影響，我們認為在 ST-FMR 的訊號中有可能混入了不同的貢獻，並在低於 80K 時急遽的增強。
Gadolinium (Gd), a rare-earth metal, is currently recognized as a material exhibiting strong spin-orbit coupling (SOC) and spin current phenomena. It transits from paramagnetic to ferromagnetic behavior at Curie temperature which is lower than room temperature. In this study, Permalloy (Ni80Fe20, Py) and Gd bilayer structure were fabricated using electron beam evaporation. The spin-torque ferromagnetic resonance (ST-FMR) was observed to investigate the contribution of spin orbit torque (SOT) induced by spin current. The spin Hall angle (θSH), representing the spin-charge conversion efficiency of Gd, was determined through analysis. Additionally, temperature-dependent ST-FMR measurements were conducted at low temperatures, and the dependence of saturation magnetization (MS) and θSH on temperature was analyzed to explore the temperature dependence of the bilayer structure and observe the effects of the magnetic phase transition at the Curie temperature of Gd. Furthermore, some variations were observed in the ST-FMR data below 80 K, significantly affecting SOT and θSH. We speculate that different contributions may be mixed in the ST- FMR signals, leading to a pronounced enhancement below 80 K.
Gadolinium (Gd), a rare-earth metal, is currently recognized as a material exhibiting strong spin-orbit coupling (SOC) and spin current phenomena. It transits from paramagnetic to ferromagnetic behavior at Curie temperature which is lower than room temperature. In this study, Permalloy (Ni80Fe20, Py) and Gd bilayer structure were fabricated using electron beam evaporation. The spin-torque ferromagnetic resonance (ST-FMR) was observed to investigate the contribution of spin orbit torque (SOT) induced by spin current. The spin Hall angle (θSH), representing the spin-charge conversion efficiency of Gd, was determined through analysis. Additionally, temperature-dependent ST-FMR measurements were conducted at low temperatures, and the dependence of saturation magnetization (MS) and θSH on temperature was analyzed to explore the temperature dependence of the bilayer structure and observe the effects of the magnetic phase transition at the Curie temperature of Gd. Furthermore, some variations were observed in the ST-FMR data below 80 K, significantly affecting SOT and θSH. We speculate that different contributions may be mixed in the ST- FMR signals, leading to a pronounced enhancement below 80 K.
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釓, 自旋轉矩鐵磁共振, 自旋軌道轉矩, 自旋霍爾角, Gadolinium, Spin-torque ferromagnetic resonance, Spin orbit torque, Spin Hall angle.