具平面內單軸各向異性之楔形鈷鐵硼特性研究

Abstract

近年來，自旋電子學（Spintronics）技術在自旋軌道矩（Spin-Orbit Torque, SOT）與磁性異質結構的研究上引起廣泛關注，其中單軸各向異性（Uniaxial Anisotropy）對磁性薄膜的磁化動力學影響更是核心議題之一。本研究的動機在於探索如何透過楔形沉積（Wedge Deposition）調控 CoFeB/Pt 結構中的單軸各向異性，並進一步分析其對磁性行為與動態特性的影響，這對於提升自旋電子學元件的性能與穩定性至關重要。 本研究製備了兩個系列的 CoFeB/Pt 樣品，皆透過磁控濺鍍機進行鍍膜，其中一組為均勻（Uniform）薄膜，另一組則透過楔形沉積使得鐵磁層（CoFeB 層）具有單軸各向異性，並調控楔形沉積與基板 x 軸的夾角範圍從 0 至 180 度，每 30 度為一個單位。透過雷射磁光克爾效應（Laser-MOKE）與振動樣品磁力儀（VSM）量測，我們確認了具有楔形結構的樣品之易磁軸（Easy Axis）與楔形方向一致。 隨後，我們利用自旋轉移力矩鐵磁共振（ST-FMR）進行頻率掃描，透過 Kittel 公式擬合獲得所有樣品的去磁場（Demagnetization Field，即 4πM_eff），並藉由共振線寬與頻率的關係進一步分析其阻尼常數（Damping Constant）。此外，透過 ST-FMR 角度掃描（Angle Scan），我們分析不同角度下的共振場變化，進一步量化單軸各向異性的大小。最後，我們對相同樣品進行鐵磁共振（FMR）量測，以比較不同量測技術的吻合程度，結果顯示兩者高度一致，驗證了本研究方法的可靠性。 本研究不僅加深了對楔形沉積 CoFeB/Pt 結構磁性行為的理解，也為磁性異質結構中單軸各向異性的調控提供了實驗依據，對於自旋電子學與未來高效磁性記憶體元件的開發具有重要價值。

In recent years, spintronics has garnered significant attention, particularly in the study of spin–orbit torque (SOT) and magnetic heterostructures. Among the key issues is the role of uniaxial magnetic anisotropy in influencing the magnetization dynamics of ferromagnetic thin films. This study aims to explore how uniaxial anisotropy in CoFeB/Pt structures can be engineered via wedge deposition, and to analyze its impact on magnetic behavior and dynamic properties—an essential step toward improving the performance and stability of spintronic devices. Two series of CoFeB/Pt samples were fabricated via magnetron sputtering: one with uniform CoFeB thickness and the other incorporating a wedge-shaped CoFeB layer to introduce uniaxial anisotropy. The deposition angle relative to the substrate x-axis was varied from 0° to 180° in 30° steps. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometry (VSM) measurements confirmed that the easy axis of the wedge-deposited samples aligned with the wedge direction. Subsequently, spin-torque ferromagnetic resonance (ST-FMR) frequency scans were conducted to extract the demagnetization field (4πM_eff) via Kittel fitting. In addition, the damping constant was obtained by analyzing the frequency dependence of the linewidth. Angular-dependent ST-FMR measurements were also performed to analyze how the resonance field varies with magnetic field direction, enabling quantitative evaluation of the uniaxial anisotropy strength. To further verify the consistency of the results, ferromagnetic resonance (FMR) measurements were conducted on the same set of samples. The comparison between the two techniques demonstrated strong agreement in terms of trends and extracted parameters, confirming the reliability of the experimental methods. This study not only deepens the understanding of magnetic behavior in wedge-deposited CoFeB/Pt structures but also provides a practical foundation for tuning uniaxial anisotropy in magnetic heterostructures. The findings have significant implications for the development of next-generation spintronic devices and high-efficiency magnetic memory technologies.