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Quantitative Phase Imaging of Magnetic Nanostructures Using Off-Axis Electron Holography.

机译：使用离轴电子全息术对磁性纳米结构进行定量相成像。

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摘要

The research of this dissertation has involved the nanoscale quantitative characterization of patterned magnetic nanostructures and devices using off-axis electron holography and Lorentz microscopy. The investigation focused on different materials of interest, including monolayer Co nanorings, multilayer Co/Cu/Py (Permalloy, Ni81Fe19) spin-valve nanorings, and notched Py nanowires, which were fabricated via a standard electron-beam lithography (EBL) and lift-off process.;Magnetization configurations and reversal processes of Co nanorings, with and without slots, were observed. Vortex-controlled switching behavior with stepped hysteresis loops was identified, with clearly defined onion states, vortex states, fluxclosure (FC) states, and O states. Two distinct switching mechanisms for the slotted nanorings, depending on applied field directions relative to the slot orientations, were attributed to the vortex chirality and shape anisotropy. Micromagnetic simulations were in good agreement with electron holography observations of the Co nanorings, also confirming the switching field of 700--800 Oe.;Co/Cu/Py spin-valve slotted nanorings exhibited different remanent states and switching behavior as a function of the different directions of the applied field relative to the slots. At remanent state, the magnetizations of Co and Py layers were preferentially aligned in antiparallel coupled configuration, with predominant configurations in FC or onion states. Two-step and three-step hysteresis loops were quantitatively determined for nanorings with slots perpendicular, or parallel to the applied field direction, respectively, due to the intrinsic coercivity difference and interlayer magnetic coupling between Co and Py layers. The field to reverse both layers was on the order of ∼800 Oe.;Domain-wall (DW) motion within Py nanowires (NWs) driven by an in situ magnetic field was visualized and quantified. Different aspects of DW behavior, including nucleation, injection, pinning, depinning, relaxation, and annihilation, occurred depending on applied field strength. A unique asymmetrical DW pinning behavior was recognized, depending on DW chirality relative to the sense of rotation around the notch. The transverse DWs relaxed into vortex DWs, followed by annihilation in a reversed field, which was in agreement with micromagnetic simulations.;Overall, the success of these studies demonstrated the capability of off-axis electron holography to provide valuable insights for understanding magnetic behavior on the nanoscale.
机译：本文的研究涉及使用离轴电子全息和洛伦兹显微镜对图案化磁性纳米结构和器件进行纳米级定量表征。这项研究集中在感兴趣的不同材料上，包括单层Co纳米环，多层Co / Cu / Py（坡莫合金，Ni81Fe19）自旋阀纳米环和带凹口的Py纳米线，它们是通过标准电子束光刻（EBL）和升力制造的。 -off过程；观察到有或没有槽的Co纳米环的磁化构型和反转过程。确定了带有阶梯式磁滞回线的涡流控制切换行为，并明确定义了洋葱状态，涡流状态，磁通闭合（FC）状态和O状态。取决于所施加的相对于缝隙取向的场方向，用于缝隙纳米环的两种不同的切换机制归因于涡旋手性和形状各向异性。微磁模拟与Co纳米环的电子全息观察非常吻合，也证实了700--800 Oe。的开关场; Co / Cu / Py自旋阀开槽纳米环表现出不同的剩磁态和开关行为，这是纳米线的函数。相对于槽的不同方向。在剩磁状态下，Co和Py层的磁化优先以反平行耦合配置排列，其中FC或洋葱状态占优势。由于Co和Py层之间的固有矫顽力差和层间磁耦合，分别定量确定了缝隙垂直于或平行于施加磁场方向的纳米环的两步和三步磁滞回线。反转两层的磁场约为800 Oe .；可视化和量化由原位磁场驱动的Py纳米线（NWs）内的畴壁（DW）运动。 DW行为的不同方面，包括成核，注入，钉扎，去钉，松弛和an灭，取决于所施加的场强。可以识别出独特的不对称DW钉扎行为，这取决于DW手性相对于围绕槽口的旋转方向。横向DW弛豫成涡旋DW，然后在反向磁场中an没，这与微磁模拟结果一致;总体而言，这些研究的成功证明了离轴电子全息术能够为理解磁行为提供有价值的见解。纳米级。

著录项

  • 作者

    He, Kai.;

  • 作者单位

    Arizona State University.;

  • 授予单位 Arizona State University.;
  • 学科 Physics General.;Nanotechnology.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 148 p.
  • 总页数 148
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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