This dissertation research has involved microscopic characterization of magnetic nanostructures using off-axis electron holography and Lorentz microscopy. The nanostructures investigated have included Co nanoparticles (NPs), Au/Fe/GaAs shell/core nanowires (NWs), carbon spirals with magnetic cores, magnetic nanopillars, Ni-Zn-Co spinel ferrite and CoFe/Pd multilayers. The studies have confirmed the capability of holography to describe the behavior of magnetic structures at the nanoscale.;The phase changes caused by the fringing fields of chains consisting of Co NPs were measured and calculated. The difference between chains with different numbers of Co NPs followed the trend indicated by calculations. Holography studies of Au/Fe/GaAs NWs grown on (110) GaAs substrates with rotationally non-uniform coating confirmed that Fe was present in the shell and that the shell behaved as a bar magnet. No fringing field was observed from NWs with cylindrical coating grown on (111)B GaAs substrates. The most likely explanation is that magnetic fields are confined within the shells and form closed loops. The multiple-magnetic-domain structure of iron carbide cores in carbon spirals was imaged using phase maps of the fringing fields. The strength and range of this fringing field was insufficient for manipulating the carbon spirals with an external applied magnetic field. No magnetism was revealed for CoPd/Fe/CoPd magnetic nanopillars. Degaussing and MFM scans ruled out the possibility that saturated magnetization and sample preparation had degraded the anisotropy, and the magnetism, respectively. The results suggested that these nanopillars were not suitable as candidates for prototypical bit information storage devices.;Observations of Ni-Zn-Co spinel ferrite thin films in plan-view geometry indicated a multigrain magnetic domain structure and the magnetic fields were oriented in-plane only with no preferred magnetization distribution. This domain structure helps explain this ferrite's high permeability at high resonance frequency, which is an unusual character.;Perpendicular magnetic anisotropy (PMA) of CoFe/Pd multilayers was revealed using holography. Detailed microscopic characterization showed structural factors such as layer waviness and interdiffusion that could contribute to degradation of the PMA. However, these factors are overwhelmed by the dominant effect of the CoFe layer thickness, and can be ignored when considering magnetic domain structure.
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机译：本论文的研究涉及使用离轴电子全息和洛伦兹显微镜对磁性纳米结构进行微观表征。研究的纳米结构包括Co纳米颗粒（NPs），Au / Fe / GaAs壳/核纳米线（NWs），具有磁芯的碳螺旋，磁性纳米柱，Ni-Zn-Co尖晶石铁氧体和CoFe / Pd多层。这些研究已经证实了全息术具有描述纳米级磁性结构行为的能力。;测量并计算了由Co NP组成的链的边缘场引起的相变。具有不同Co NP数量的链之间的差异遵循计算表明的趋势。在具有旋转非均匀涂层的（110）GaAs衬底上生长的Au / Fe / GaAs NW的全息照相研究证实，壳中存在Fe，并且壳起着条形磁铁的作用。在（111）B GaAs衬底上生长有圆柱形涂层的NW上未观察到边缘场。最可能的解释是磁场被限制在壳内并形成闭环。使用边缘场的相位图对碳螺旋中的碳化铁核的多磁畴结构进行成像。该边缘场的强度和范围不足以利用外部施加的磁场来操纵碳螺旋。对于CoPd / Fe / CoPd磁性纳米柱，没有发现磁性。消磁和MFM扫描排除了饱和磁化强度和样品制备分别降低了各向异性和磁性的可能性。结果表明这些纳米柱不适合用作原型位信息存储设备。; Ni-Zn-Co尖晶石铁氧体薄膜在平面图中的观察表明其为多晶磁畴结构，且磁场在平面内取向仅没有优选的磁化分布。这种畴结构有助于解释这种铁氧体在高共振频率下的高磁导率，这是一个不寻常的特征。;使用全息图揭示了CoFe / Pd多层膜的垂直磁各向异性（PMA）。详细的显微表征显示出可能导致PMA降解的结构因素，例如层波纹度和相互扩散。但是，这些因素被CoFe层厚度的主导作用所淹没，在考虑磁畴结构时可以忽略不计。
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