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Optical control of ultrafast spin-wave relaxation by magnetic anisotropy in a ferromagnet.

机译：通过铁磁中的磁各向异性实现超快自旋波弛豫的光学控制。

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摘要

This thesis presents an investigation of the damping of spin waves in ferromagnetic Au(3 nm)/Ni(10 nm)/MgO(001) thin films using the time-resolved Magneto-optical Kerr Effect (TR-MOKE) and ferromagnetic resonance (FMR) techniques. In the optical measurements, a 150 fs, 800 nm laser beam pulse is split into pump and probe components. The pump pulse, containing most of the beam energy, thermally excites coherent spin precession. The weaker probe pulse, time-delayed by a variable beam path, captures the magnetization dynamics via the polar MOKE effect, and oscillations are observed as a function of external field amplitude and direction. The extracted precession frequency is consistent in both the optical and resonance techniques; however, additional damping is observed in the TR-MOKE measurements that is strongly correlated to the orientation of the magnetization with respect to the magnetic anisotropy. The damping is identical in TR-MOKE and FMR only when the external field is applied near the easy axis of magnetization. The enhanced damping in TR-MOKE is shown to be a consequence of pump-induced inhomogeneous broadening in the presence of magnetic anisotropy, a result of differing temperature recovery profiles for the magnetization and magnetic anisotropy. Finally, a simple model is developed which explains the anisotropic damping: mode broadening occurs in regions where the magnetization changes rapidly with respect to changes in the external field, as determined by the curvature of the magnetic free energy. We thus introduce a novel damping effect in TR-MOKE: pump-induced anisotropic damping (PIAD).
机译：本文利用时间分辨磁光克尔效应（TR-MOKE）和铁磁谐振研究了铁磁Au（3 nm）/ Ni（10 nm）/ MgO（001）薄膜中自旋波的阻尼（ FMR）技术。在光学测量中，将150 fs，800 nm的激光束脉冲分成泵浦和探头组件。包含大部分光束能量的泵浦脉冲热激发相干自旋旋进。可变脉冲路径延迟了较弱的探测脉冲，通过极性MOKE效应捕获了磁化动力学，并且观察到振荡是外部磁场幅度和方向的函数。提取的进动频率在光学和共振技术上都是一致的。但是，在TR-MOKE测量中观察到了额外的阻尼，该阻尼与磁化相对于磁各向异性的方向密切相关。仅当在易磁化轴附近施加外部磁场时，TR-MOKE和FMR中的阻尼相同。 TR-MOKE中增强的阻尼被证明是在磁各向异性存在下泵引起的不均匀展宽的结果，这是磁化和磁各向异性温度恢复曲线不同的结果。最后，开发了一个简单的模型来解释各向异性阻尼：模态加宽发生在磁化强度随外部磁场变化而迅速变化的区域，这取决于磁自由能的曲率。因此，我们在TR-MOKE中引入了一种新颖的阻尼效果：泵引起的各向异性阻尼（PIAD）。

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  • 作者

    Smith, Kevin James.;

  • 作者单位

    The College of William and Mary.;

  • 授予单位 The College of William and Mary.;
  • 学科 Physics General.;Physics Electricity and Magnetism.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 87 p.
  • 总页数 87
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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