Current-driven magnetic sources at microwave frequency

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Microwave frequency sources are a critical component of technology for applications ranging from mobile devices to communications to computing. There is a need to develop extremely compact sources, and to develop sources that are agile, meaning their frequency can be shifted on the shortest possible timescale. A good candidate is nanoscale magnetic oscillators that produce highly tunable microwave frequencies through the application of d.c. current. Singly, these magnetic oscillators have insufficient output power and too broad a linewidth to be applied in technology, however, if they can be connected to each other so that they synchronize their microwave output, both the power and the linewidth problem can be overcome. While a few magnetic oscillators have been coupled together previously, it has been difficult to design them so that they synchronize in a scalable way. Additionally, understanding the nanoscale magnetic interactions between oscillators is an interesting scientific problem that has implications beyond technology. This project will train both undergraduate and graduate students in an interdisciplinary environment, and it will offer research experience for science teachers.In this proposal, the research team introduces three innovate concepts to overcome the challenge of scalably synchronizing nanoscale magnetic oscillators. First, they propose to design, model and fabricate lateral magnetic oscillators driven by the spin Hall effect in a periodic array using concepts from the emerging field of magnonics. Second, they will employ spatiotemporal magnetic microscopy to experimentally examine the dynamical modes of these structures, which will help reveal how individual STOs are coupled to its neighbors in real devices. This is a new opportunity offered by recent breakthroughs in lateral spin Hall oscillator devices because magnetic oscillator networks were previously based on direct injection, vertical transport devices. In those devices, the magnetic layers are buried and very difficult to image. The availability of imaging creates an opportunity to engineer devices based on specific, device-level insight. The third innovate concept is to use stroboscopic imaging to study loss mechanisms from magnetic modes. Traditionally, stroboscopic methods are blind to incoherent processes, like the coupling between spin wave modes that can lead to dynamically enhanced magnetic damping. By combining microwave driving fields that are both commensurate and incommensurate with the stroboscope, the research team will examine how energy can be transferred between useful magnetic modes and spurious magnetic modes. The insights from this research will enable new and better designs to synchronize magnetic oscillators.