All Optical, Tunable THz Magnonic Devices

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The terahertz portion of the spectrum is the challenging boundary region between higher frequency optical (infra-red) technology and the microwave realm. The terahertz spectrum offers many potential advantages across a range of applications and industries, including communications and information technology, biological imaging and health sciences, chemical sensing and other security applications, and even spaceborne astronomy. This project will examine the fundamental properties of a class of materials called ferrimagnets and use those materials in novel ways to develop a new kind of terahertz source for very high speed communications and information processing applications. This project will examine the properties of ferrimagnets in thin films, at different temperatures and at very high magnetic fields. Furthermore, the unique qualities of ferrimagnets will be used in a novel magnetic device that achieves unprecedented speed by using extremely short pulses of light to excite motion of the magnetic properties of the ferrimagnet. The scientific understanding of the fundamental properties of these materials and their implementation in devices is crucial for the next generation of magnetic devices and ultra-high speed information technology that supports the evolving 21st century digital economy. The research will support two graduate students from under-represented groups in Physics, will expose up to six undergraduates in advanced research, and will help foster collaboration with the graduate program of a Minority Serving Institution.One promising approach to realize practical terahertz (THz) electronics relies on spintronics, which extends and amplifies the properties of conventional electronics via the manipulation of electron spin. The proposed novel device architecture will significantly narrow the bandwidth of spintronic THz sources of while also providing for wide tunability of the carrier frequency. The core of the proposed device is a magnetic tri-layer system consisting of a Polarizer layer, a non-magnetic spin transport layer, and an Emitter layer, all grown on optically transparent substrates. The THz carrier frequency is governed by spin wave modes in the Emitter layer and the frequency of the spin waves is determined by magnetic properties (saturation magnetization, g-factor, spin wave stiffness, etc.) of the Emitter. Ferrimagnetic materials enable a very large degree of control of magnetic properties of the Emitter and hence in the frequency of the THz emission. The THz scale dynamics of these prototype all-optical devices will be studied with fs time-resolved magneto-optic Kerr effect [tr-MOKE] and slower spin dynamics will be investigated with ferromagnetic resonance [FMR]. Moreover, the ferrimagnetic dynamics will be examined in detail using element-specific spectroscopic techniques (x-ray detected FMR [X-FMR] and fs-scale high harmonic generation [HHG]). The research will address three fundamental issues: (1) Understanding in detail the competing exchange interactions that give ferrimagnets their unique properties; (2) Harnessing these properties for the improvement of spintronic THz emitters; and (3) Modifying the THz-scale magnetic response using extreme magnetic fields.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.