Waves are in many parts of our lives, from communication to computation, and are a subject of intense research. In particular, micro and millimeter waves have been paid great attention for next-generation technologies, e.g., 5G/millimeter-wave wireless network, due to the ever-increasing demand in mobile data by the explosion of mobile users and IoT. However, the fabrication of reconfigurable high-frequency devices and components has been a challenge due to the lack of appropriate materials. Recent developments in chiral and magnetic meta-materials that facilitate asymmetric spin-wave propagation are promising for creating microwave circulators and diodes based on spin waves. These spin waves are highly configurable because the magnetic interactions in chiral magnets and asymmetric magnetic multilayers can be tailored, and these materials are highly sensitive to external magnetic fields and laser pulses for further manipulation. The demonstration of such configurable, power-efficient, and versatile microwave components will pave the way towards new high-frequency communication devices, which can be used in various applications, including entertainment, security, and remote patient treatment.

The joined effort between Oklahoma State University and Nanoscale Spin Dynamics group at NIST, Boulder, will accelerate materials discovery and device characterization for superior and reconfigurable microwave components that can operate from a few GHz up to THz frequencies. The proposed research will advance the fundamental understanding of non-reciprocal spin-wave propagation in chiral magnetic materials, which is caused by asymmetric exchange interaction in them due to the broken inversion symmetry. These spin-waves are non-trivial compared to light or other waves, but they can be highly tractable by tailoring magnetic interactions, applying external electric and magnetic fields, or exciting with ultrashort pulses. Control of magnetic interactions will be achieved by engineering interfaces of magnetic material and adjacent metal layers to minimize magnon scattering but maintain high non-reciprocity. Numerical micromagnetic simulations will be used to optimize device performance and to better understand spin-wave propagation in complex heterostructures. For this purpose, the team will (i) grow and synthesize low-damping chiral magnetic materials and thin films, (ii) precisely characterize their structural and magnetic properties, and (iii) fabricate micro and nanoscale devices for the development of device concepts. Broadband ferromagnetic resonance spectroscopy, magnetometry, Brillouin light scattering spectroscopy, magnetotransport, and heterodyne magneto-optical microwave microscopy are the techniques to be employed in this investigation.

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.

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Oklahoma State University
United States
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