Technical: This project uses optical techniques to study MgO heterostructures, an important material for spin-based electronics. It aims to addressing several important questions regarding giant tunneling magnetoresistance (TMR) in MgO-based magnetic tunnel junctions: the source of the bias dependence of TMR, the role of materials imperfections on the TMR, and valid assumptions regarding magnetic microstructure in both the lateral and vertical directions for spin torque. The project applies optical second harmonic generation (SHG) to directly address these important issues which are central to MgO-based magnetic tunnel junctions and magnetic random access memory. Second harmonic generation will be utilized in situ to perform real-time monitoring of interfaces during molecular beam epitaxy (MBE) growth. It will be used to characterize interfacial magnetism and compare with the bulk magnetism. Second harmonic generation also has the ability to directly measure the barrier heights of MgO with spin resolution, and could even give information about the effective mass related to the tunneling process. The experimental research will also investigate magnetic microstructure in spin-torque devices by driving the devices resonantly with GHz ac currents, and used synchronized optical pulses to measure possible phase shifts between interface and bulk magnetization dynamics. In addition, an apertureless near-field optical microscopy technique will be developed to work in conjunction with the time-resolved second harmonic generation spectroscopy to probe the lateral microstructure.
The project addresses basic research issues in a topical area of materials science with high technological relevance. Magnetic random access memory (MRAM) possesses the potential to combine the existing mainstream memories, used in every aspect of modern lives, into a universal memory. However, the challenges coexist with this unprecedented opportunity. Solving some of the challenges will significantly contribute to the advances of this great technology, therefore have a great impact to the society. Students working on this project will gain a unique training in materials synthesis and optical spectroscopy, which will help them develop careers in the industrial job market. Due to the diverse demographic surrounding University of California at Riverside, there is ample opportunity to help enhance diversity in the technological workforce. The PIs are committed to a number of outreach activities including undergraduate and high school participation in research, development of undergraduate and graduate coursework to reflect the current research activities, and the management of a weekly nanoscale physics journal club.
