Collaborative Research: Spin Torque Oscillators Based on Electric and Thermal Spin Currents in Self Assembled Ferromagnetic Nanowire Arrays

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Intellectual merit of the proposed activity: The project aims to study spin transfer torques driven by electric and thermal spin currents by utilizing ordered arrays of self-assembled ferromagnetic nanowires, and to investigate the nonlinear magnetization dynamics in these closely packed spin torque oscillator arrays. The objectives of this collaborative research are: (i)to study electric and thermal spin torques generated by a ferromagnetic nanowire in response to electric potential and temperature gradients; (ii) to study nonlinear collective magnetization dynamics in the hexagonally packed two dimensional arrays of strongly coupled spin transfer torque oscillators; and(iii)to develop a high-power microwave voltage controlled oscillator based on an array of phase locked spin torque oscillators.The proposed array of spin torque oscillators consist of hexagonally ordered cobalt nanowires electrodeposited in anodized alumina template. These nanowires will serve as spin current injectors into a thin ferromagnetic film common to all injectors. Spin currents will be generated by either voltages or thermal gradients applied across the nanowires. Coupling among the individual spin torque oscillators will be facilitated by spin waves propagating in the common ferromagnetic layer. Ultrafast electrical detection of magneto-dynamics, broadband ferromagnetic resonance and magnetic force microscopy will be used to characterize the nonlinear magnetization dynamics in the array of spin torque oscillators. The proposed research will advance the understanding of the large-amplitude magnetization dynamics driven by electric and spin currents, which is important for the development of the next generation ultrafast and non-volatile magneto-electronic devices such as hard drive read heads and wireless communication systems. This research program will also benchmark the relative strength of thermally driven spin currents against the more common spin-polarized electric currents in the same system.Broader impact of the proposed activity: The microwave voltage controlled oscillator developed in this research will have a significant technological impact on information storage and telecommunication industries. PhD students, as well as undergraduates and high school students will take part in this program under the guidance of the investigators. The practical training in nanofabrication and unique measurement techniques offered by this program will prepare specialists for the USA magneto-electronics industry that are currently undergoing a rapid transition from micro- to nano-scale. The PIs will continue to attract underrepresented students from minority-serving institutions, such as California State Universities, as well as local K-12 students to participate in the research projects. In the education curriculum, all investigators have developed courses on nanoscience and nanotechnology with a series of demonstrations for graduate and undergraduate students.This project is jointly funded by the Electronics, Photonics, and Magnetic Devices Program (EPMD) in the Division of Electrical, Communications and Cyber Systems (ECCS) and by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR).