Quantitative microanalysis techniques for magnetic nanostructures

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University of Alabama Libraries

Microanalysis techniques are used to characterize magnetic nanostructures. To advance these materials in many applications, it is necessary to understand the microstructure. For example, subtle compositional fluctuations within a nanostructure can significantly influence the material properties. In this work, microanalysis techniques have been used to quantify composition, volume fraction, and long-range order parameter in magnetic nanostructures. A methodology for determining an optimal voxel dimension range was developed using a model system for the experimentally collected atom probe tomography data. The influence of voxel dimension on volume fraction and composition of chemically partitioned phases is examined. Atom probe tomography is used to understand the influence of Pt enrichment at grain boundaries in the A1 to L10 polymorphic phase transformation. The Pt enrichment at grain boundaries in atom probe tomography analysis provides experimental verification of modeling predictions of Pt surface segregation. It is also observed that upon phase transformation to L10, the Pt grain boundary enrichment decreased. Field ion microscopy and atom probe tomography is used to evaluate the field evaporation behavior of (001) planes in ordered FePt. Both experimental and simulation results have shown that the difference in evaporation field between the two components of the alloy contributed to the trajectory aberrations near the (002) pole and zone axes. The model system shows that chemical order within a structure introduces aberrations in the reconstruction of the atomic planes limiting the spatial and chemical fidelity of characterizing such structures using current reconstruction methodologies. Finally, a comparison of the experimental results to simulations is used to assess the viability of electron diffraction in the quantification of S in FePt thin films and nanoparticles. A multislice approach was used to simulate CBED patterns of FePt films with various thicknesses, compositions, orientations, and S values. In general, electron diffraction provides a technique to determine order parameter of small volumes with the implementation of multislice simulations.

Electronic Thesis or Dissertation
Nanoscience, Engineering, Metallurgy