Principal Investigator: Carl E. Patton Co-Principal Investigator: Mingzhong Wu
The research objective is to use standing spin wave resonance (SSWR) in magnetic films to develop a new class of millimeter wave radar and signal processing devices that are compatible with monolithic integrated circuit technology. The program will use thin films with pinned surface spins that support SSWR modes across the film thickness. In very thin films, these modes give a large effective exchange field that shifts the corresponding FMR frequencies into the millimeter wave range. The target film materials will include ferrite films and high-magnetization metallic films, as well as multilayer structures. The films/structures will be produced by pulsed laser deposition, e-beam evaporation, and magnetron sputtering, and integrated into prototype devices such as circulators, isolators, notch filters, bandpass filters, phase shifters, and directional couplers.
The fabrication of new nano films and structures will advance film deposition science and technology. The characterization work will advance the understanding of magnetic loss processes at millimeter wave frequencies. The device development will advance millimeter wave device physics and technology. The new devices will have a major impact in both commercial and defense technology arenas.
The impact on the fields of nano-materials technology and millimeter wave science and technology will be substantial. Underrepresented groups will be involved through the Colorado State University (CSU) diversity recruitment and retention program and the Army sponsored summer Research and Engineering Apprenticeship Program. Experiential learning at the K-12 level will be promoted through a partnership with the CSU Little Shop of Physics.
The main findings obtained in this NSF project are as follows. (1) We found that, through a four-step temperature control process, it was possible to use pulsed laser deposition (PLD) to grow M-type barium hexagonal ferrite (BaM) thin films with high remanent magnetization and low microwave loss. (2) We demonstrated that, through optimized PLD processes, one could grow yttrium iron garnet (YIG) nano films with narrow ferromagnetic resonance (FMR) linewidths. (3) We demonstrated a sandwich electrode approach that could allow for the deposition of high-quality YIG thin films on electrodes. (4) We demonstrated the feasibility of using the excitation of FMR, broadband magnetostatic waves, or confined magnetostatic waves in BaM thin films to fabricate planar millimeter wave notch filters and phase shifters. (5) We found that there existed spin-wave resonance (SWR) excitations in "natural" Permalloy nano films. Such excitations result from the pinning of film surface spins at the film-substrate interface and can significantly reduce the SWR fields in very thin films. (6) We observed multiferroic responses in W-type barium hexagonal ferrites. (7) We demonstrated the control of ferromagnetic relaxation in FeCo nano films through the use of different seed layers. (8) We found that one could effectively tune the FMR linewidth in FeGaB nano films through a change in boron content. (9) We demonstrated the tuning of FMR linewidths in YIG films via the spin Seebeck effect. (10) We demonstrated the feasibility of using chaotic spin waves in magnetic thin films to make tunable microwave chaotic oscillators. These findings comprise significant contributions to the development of high-quality magnetic metallic nano films, YIG nano films, and hexagonal ferrite thin films, the understanding of high-frequency loss mechanisms in magnetic nano films, and the development of new microwave and millimeter wave device concepts. The project provided research opportunities to one Research Scientist, three Ph.D. students, two international exchange graduate students, five undergraduate students, and three high-school students. Graduate students who participated in this project had presented the results in several conferences and summer schools. The PI and co-PI had given a number of talks in university colloquia and international conferences. Supported in part by this project, a magnetron sputtering system was installed. This system serves to enhance the capability for thin film deposition at Colorado State University.