Magneto-optical imaging of nanomagnetic structures

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In recent years, research on the use of magnetic properties of materials for electronics (spintronics) and data storage has grown tremendously. In both areas, spintronics and magnetic storage, size and operational speed are defining properties of a device. As the size of a magnetic element is reduced below a few hundred nanometers, another qualitative change occurs as the magnet can only sustain a single domain. This has severe consequences for dynamic properties, which do not depend on domain wall motion anymore. To this day, the time scales over which magnetization changes on the single-domain levels occur are not known. It is therefore essential to develop the capabilities to measure these fundamentally and technologically relevant quantities that present the ultimate intrinsic limit for the speed of nanoscale magnetic devices. We will study the magnetization dynamics of nanoscale magnetic structures with high temporal and spatial resolution as an area of research with large impact on (nano)-magnetic applications. Ultrafast optical methods such as magneto-optical Kerr spectroscopy will be used to provide the time resolution required to resolve changes in the magnetization direction of single-domain particles. Based on an integrated ultrafast spectroscopy system with near-field scanning microscopy capabilities, a setup for the magneto-optical measurement of the magnetization dynamics of single single-domain (nano)-magnetic structures will be built. Subsequently, measurements on nanomagnetic structures of varying sizes and shapes will be carried out to gain a qualitative and quantitative understanding of the magnetization reversal time scales and mechanisms.In addition, highly sensitive magneto-optical spectroscopy methods will be developed. The detection of small magneto-optic reflection signals from individual nanostructures requires exquisite sensitivity. Therefore, cavity enhancement of the magneto-optical Kerr effect will be studied to extend this technique to the ultrafast single-particle regime. In the course of the project, cavity enhancement will first be investigated in larger samples or arrays of nanomagnets before then being applied to individual single-domain particles. The work proposed here is expected to have significant broader impact. As magneto-optics and spintronics evolve and device dimensions shrink further, sensitive methods to measure magnetic properties will play an important role in determining the limitations of such devices. Over the course of the program, graduate students will be trained in two key areas of experimental research, ultrafast spectroscopy and scanning microscopy. In addition, undergraduates will be actively involved in the project and aspects of this research will be incorporated into a multidisciplinary graduate class in nanotechnology currently being developed at UC Santa Cruz.