Materials science encompasses a broad range of different materials and applications; however, at its core is the drive to understand structure-property relationships and exploit them to engineer new materials that out-perform current ones. A unifying theme in this is materials characterization: the study of material structure, properties, processing, and performance.
Next-generation electronic devices will likely exploit more than just charge transfer and bulk magnetism to compute and store data. Instead, they will also make use of the inherent spin of the electron in so-called spintronic devices. These devices promise higher densities and lower operating power demands, thus significantly increasing performance. Using electron microscopy, the structures of novel magnetic materials are characterized across many length scales, as well as their electronic and magnetic properties using spectroscopy and theory.
Advances in aberration corrected scanning transmission electron microscopy (STEM) make it possible to investigate materials' structures at the atomic level on a routine basis. The growth of high quality magnetic thin films is essential to their application in future devices. Characterization of the growth mechanism of pyrochlore Nd2Ir2O7 thin films, as well as their structure and composition is presented, with a thermodynamic explanation of the observed phenomena. In addition, atomic-scale defects and ordering in double perovskite Sr2CrReO6 thin films were studied both experimentally, as well as via a quantum mechanical electron scattering model. It is found that three-dimensional ordering information can be extracted from two-dimensional high-angle annular dark field STEM images. This is due to the fact that as the electron travels through the specimen, it is encoded with such information before being collected to form the image. Using certain sample- and experiment-specific parameters, the experimental data can be compared to simulated results to access the three-dimensional ordering data.
In addition to thin films, the electronic properties of bulk double perovskite A2BOsO6 (A=Ca, Sr; B=Cr, Fe, Co) are studied using electron energy-loss spectroscopy. The results are explained through the use of first principles calculations. Studying electronic structure in the electron microscope allows for high spatial resolution investigations into the effect of interfaces and other defects on electronic structure and their implications in magnetic properties.
Finally, magnetic skyrmion materials are studied in situ using Lorentz TEM and Lorentz differential phase contrast (DPC) STEM as a function of applied magnetic field and temperature. These materials may allow for ultra-high-density storage requiring orders of magnitude less energy. Skyrmions are studied in both bulk and thin film geometries. The size, temperature range, and field stability of skyrmions are investigated in two main classes of materials: B20 thin films and heterostructures, as well as perovskite bilayers. Progress is made on the development of zero- and low-field Lorentz DPC-STEM and its application to imaging different skyrmion types with improved spatial resolution and sensitivity.