利用投影式向量磁鐵進行電性量測

Abstract

由於自旋軌道矩有潛力實現尖端的高速自旋電子裝置，像是自旋軌道矩磁性隨機存取記憶體及自旋振盪器，因此新穎材料的自旋軌道矩在這幾年被大量的研究。通常有幾種方法常被使用來分析自旋軌道矩，像是自旋軌道矩鐵磁共振、諧波霍爾技術及磁滯曲線平移量測。然而，在同樣一個小型電磁鐵上進行這些分析技術是相當有挑戰性的，因為這些量測各自需要不同的磁場組合。另外，大部分的角相依量測都是利用打線連接的試片來進行。但打線的過程相當耗時，且會限制受測裝置的數目，使得此種量測執行起來效率低落。 在本篇論文中，透過深度學習模型的幫助，投影式向量磁鐵精準的磁場校正能夠被實現。這些模型讓一顆小型向量磁鐵能執行磁場掃動、角度掃動和磁滯曲線平移量測。我們展示了利用掀離法製備之試片來容易的完成角相依電性量測，包含平面霍爾及異向性磁阻之量測。而且我們利用具垂直異向性之鎢/鈷鐵硼異質結構在向量磁鐵上展示自旋軌道矩分析技術，包含典型及角相依之磁滯曲線平移量測。透過向量磁鐵和包含兩組分離電磁鐵的傳統架構所萃取出之阻尼像自旋軌道矩效率值相當吻合。除此之外，利用向量磁鐵系統，我們也展示了包含平面霍爾修正項之諧波霍爾量測和電流引發磁矩翻轉量測。本篇論文提供了謹慎操縱向量磁鐵和有效率的執行自旋軌道矩分析技術之進階方法。

Since spin-orbit torques (SOT) have the potential to realize high-speed spintronics devices at the cutting-edge including SOT-magnetic random access memory (SOT-MRAM) and spin oscillators, SOT of novel materials have been widely studied these years. To characterize SOT, several methods are adopted including spin torque ferromagnetic resonance, harmonic Hall technique and hysteresis loop shift measurement. Nonetheless, it is challenging to carry out these characterization protocols with a compact electromagnet setup as different magnetic field combinations are required. What’s more, most angle-dependent measurements are performed on samples fabricated with a wire-bonding process, which could take a huge amount of time and restrict the number of devices being tested, making such measurements inefficient. In this thesis, precise magnetic field calibration of a projected vector field magnet is realized with the assistance of deep learning models. The trained models make magnetic field scans, angle scans, and hysteresis loop shift measurements possible within a compact vector magnet setup. Angle-dependent transport measurements including planar Hall and anisotropic magnetoresistance are shown to be easily done with lift-off devices. Moreover, SOT characterizations on W/CoFeB magnetic heterostructures with perpendicular anisotropy are further demonstrated on the projected vector field magnet via typical loop shift and angle-dependent loop shift measurement. The damping-like SOT efficiencies extracted from the vector magnet and the traditional measurement configuration comprised of two separated electromagnets are consistent. Also, harmonic Hall measurement complemented with planar Hall correction as well as current-induced SOT switching are demonstrated on the vector magnet system. This thesis provides an advanced method to carefully manipulate a vector magnet and to efficiently perform various SOT characterizations.