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Quantum confinement and symmetry breaking in layered magnetic nanostructures.

机译:层状磁性纳米结构中的量子限制和对称破坏。

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摘要

The effects quantum confinement and symmetry breaking are believed to play a crucial role in determining the magnetic properties of magnetic thin films and multilayers. We investigated the quantum confinement using Angle-Resolved Photoemission Spectroscopy (ARPES) and the symmetry breaking using the Surface Magneto-Optic Kerr Effect (SMOKE).;The quantum well (QW) states in a Cu thin film grown on a Co(001) substrate were directly observed using ARPES, which measured the momentum-resolved density-of-states. Using a wedged Cu film to vary the thickness of the QW, we observed a shifting of the QW energy levels that occurs in order to satisfy the standing wave boundary conditions along the normal direction. This behavior was analyzed within the framework of the phase accumulation model. In addition, we developed a method to map out the nodes and antinodes of the standing wave by inserting a monolayer of Ni into different positions inside the well. In terms of magnetic properties, the relation between the QW states and the oscillatory magnetic coupling was investigated by measuring both phenomena on the same sample. We also observed a quantum interference effect on the QW states which shows that the oscillations in the magnetic coupling strength with ferromagnetic thickness originate from a modulation of the QW density of states. We also examined the effects of in-plane motion, which leads to the QW subbands. Finally, a study of the electronic coupling in double QW systems shows that the length scale of tunneling across the hybridization gap is only a few atomic layers.;The step-induced magnetic anisotropy in Fe on stepped Ag(001) and Co on stepped Cu(001) was investigated using SMOKE. Regular atomic steps on a (001) surface break the four-fold rotation symmetry to induce an in-plane uniaxial magnetic anisotropy. To explore the intrinsic relation between the lattice symmetry breaking and the induced magnetic anisotropy, we developed a curved substrate that allowed a continuous range of vicinal angles to be present on a single sample. Previous studies only looked at a fixed vicinal angle. We found that the step-induced magnetic anisotropy strength varied quadratically with the step density for Fe/stepped Ag(001), but linearly for Co/stepped Cu(001). The results are analyzed within a nearest neighbor Neel pair-bonding model, which suggests that the differences are due to the differences in the local bonding of these two structures. Both pair-bonding and strain effects are analyzed.
机译:据信量子限制和对称破坏的影响在确定磁性薄膜和多层的磁性方面起着至关重要的作用。我们研究了使用角度分辨光发射光谱(ARPES)进行的量子限制以及使用表面磁光克尔效应(SMOKE)进行的对称破坏。;在Co(001)上生长的Cu薄膜中的量子阱(QW)状态使用ARPES直接观察底物,该方法测量了动量分辨的状态密度。使用楔形的Cu膜来改变QW的厚度,我们观察到为了满足驻波边界条件沿法线方向发生的QW能级移动。在相积累模型的框架内分析了此行为。此外,我们开发了一种方法,可以通过在孔内的不同位置插入单层Ni来绘制驻波的波节和波腹。在磁性方面,通过测量同一样品上的两种现象研究了QW态与振荡磁耦合之间的关系。我们还观察到了对QW态的量子干涉效应,这表明具有铁磁厚度的磁耦合强度中的振荡源于对QW态密度的调制。我们还检查了平面运动的影响,这导致了QW子带。最后,对双量子阱系统中电子耦合的研究表明,穿越杂化缝隙的隧穿的长度尺度仅是几个原子层。;在阶梯状Ag(001)上的Fe和在阶梯状Cu上的Co中的阶梯感应磁各向异性(001)使用SMOKE进行了研究。 (001)表面上的规则原子台阶破坏了四重旋转对称性,从而引起面内单轴磁各向异性。为了探究晶格对称性破坏与感应磁各向异性之间的内在联系,我们开发了一种弯曲的基板,该基板允许在单个样品上出现连续范围的邻角。先前的研究仅关注固定的邻角。我们发现,Fe /阶梯状Ag(001)的阶梯感应磁各向异性强度随阶梯密度呈二次方变化,而Co /阶梯状Cu(001)的阶梯感应磁各向异性强度随阶梯密度呈线性变化。在最近的邻居Neel对键模型中分析了结果,这表明差异是由于这两种结构的局部键的差异所致。分析了成对键合和应变效应。

著录项

  • 作者

    Kawakami, Roland Kenji.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 1999
  • 页码 123 p.
  • 总页数 123
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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