Antiferromagnetic Nano- oscillators Enabled by Unconventional Topological Spin Current

About This Grant

High frequency electromagnetic signals hold a significant promise for applications in communications, medical imaging, security, and more. Spintronics based technologies present an appealing route for high-frequency signal generation. For example, continuous rotational dynamics of the order parameter (magnetization or Néel vector) in magnetic systems driven by charge current, through the mechanisms of spin-orbit torque, can be used to realize conceptualized nano-oscillator devices for generating high frequency signals. Specifically, antiferromagnets based nano-oscillators, wherein the output signal frequency can range between gigahertz to terahertz range due to inherently ultra-fast rotational spin dynamics, has only recently been proposed and experimental demonstration of such a device remains critically missing. This research program aims at the first demonstration of prototype antiferromagnet based nano-oscillator devices by building a comprehensive understanding of spin dynamics in a new class of antiferromagnets and by providing unique strategies for electrically driving and detecting the broadband spin dynamic in antiferromagnets by exploiting unconventional form of spin current in topological semimetals. The project will impact society through the innovation to realize transformative high-frequency devices for next-generation technologies. This project will enable the training of next-generation researchers in the United States for workforce development. Through this project, a graduate student and undergraduate student(s) will be trained in experimental techniques, critical thinking, and solving complex research problems. Also, outreach events to kindle scientific interest and provide interactions and mentorship for middle school and high school students will be explored. Continuous rotational dynamics in antiferromagnets can enable next-generation device technologies, such as tunable and broadband sources and detectors of gigahertz to terahertz frequency signals. However, the understanding of dynamic phenomena in antiferromagnets, e.g., resonance modes, Néel vector precession, and magnon transport, which is essential to build antiferromagnet-based nano-oscillators, remains in its infancy. The discovery of magnetic order and unconventional topological spin current in two-dimensional systems provides a unique material platform to demonstrate antiferromagnet-based nano-oscillators. Relatively weak but highly tunable interlayer coupling in two-dimensional magnets, compared to traditional antiferromagnetic materials, provides a knob to control the magnetic state and response of the system, including accessing different dynamical regimes, and in turn, different frequency and response time ranges. Most importantly, to realize a prototype antiferromagnet-based nano-oscillators, one needs to experimentally demonstrate two key operations, i.e., charge current driven spin dynamics in antiferromagnets via spin-orbit torque mechanisms and subsequent broadband detection (electrical or other means) of spin dynamics in antiferromagnets in mesoscopic samples. This research program is aimed at demonstration of prototype antiferromagnet-based nano-oscillator devices and the specific scientific goals of this research program are threefold: (1) Characterization of magnetic order and dynamical response in mesoscopic two-dimensional antiferromagnetic systems; (2) Demonstration of antiferromagnetic spin dynamics driven by unconventional topological spin current; (3) Demonstration of antiferromagnet-based nano-oscillator device functionalities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.