Development of a Ferrimagnetic Terahertz Oscillator

The terahertz (THz) band of the electromagnetic spectrum is a largely untapped resource, with potential applications in imaging, spectroscopy, sensing, computing, and communications. This project aims to fill a gap in THz technology by developing a novel compact high-power source that operates at room temperature, and opening up the THz band to applications that are currently limited by the bulky and/or low temperature THz sources available today. The project will train 2 graduate students and at least 2 undergraduate students in an interdisciplinary area of science and engineering. Community college students and underrepresented minority college students will be included in summer research programs. Results from the research will be incorporated into coursework in the Materials Science and Engineering department, including online subjects that are available to the public free. The PIs will organize The NanoObservatory during the Cambridge Science Festival which explains lithography and microscopy to the general public, and will offer lectures and activities in nanotechnology through the Dow-MIT ACCESS program. The objective of the proposed work is to engineer novel terahertz (THz) sources by harnessing the dynamical oscillatory behavior of a ferrimagnet driven by an electric current in an adjacent heavy metal. The THz band of the electromagnetic spectrum is a largely untapped resource, with potential applications in imaging, spectroscopy, sensing, computing, and communications. Standing in the way of widespread applications is a lack of efficient, tunable broadband THz sources, and a means of implementing them in small form factor devices. The proposed research will demonstrate a revolutionary frequency-tunable solid-state THz emitter with figures of merit that are unmatched by the current state of the art. The key innovation that will enable the proposed THz source is the dipole radiation of a large uncompensated net magnetization in a ferrimagnet driven into THz precession near its angular momentum compensation point. Spin-Hall current-driven coherent auto-oscillations with frequency exceeding 1 THz will be achieved in low-damping oxide ferrimagnets in which antiferromagnetic exchange interactions enable ultrafast dynamics. The fundamental research will yield new insights into high-speed antiferromagnetic-like spin dynamics and spin-charge interconversion as well as new approaches to engineer multi-axis magnetic anisotropy landscapes to tailor dynamical magnetization trajectories. The tunable spintronic THz generators will serve as proof-of-concept compact THz sources. The project will train two graduate and two undergraduate students. Results from the research will be incorporated into coursework in the Materials Science and Engineering department. Public outreach will include The NanoObservatory during the Cambridge Science Festival and lectures and activities in nanotechnology through the Dow-MIT ACCESS program. 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.