Parametric Amplification of Forward Volume Spin Waves by Surface Acoustic Waves

Research in recent years has shown a great interest in spin waves as a medium for storing, processing and transporting information to build small, low-powered, and high-speed devices for magnonic logic circuits and signal processing applications. However, spin waves cannot travel long distances in most magnetic materials due to intrinsic damping. This limits the use of spin waves in applications that require transferring information over long distances. In this work, we are investigating a mechanism to amplify forward volume spin waves (FVSW) parametrically with surface acoustic waves (SAW). We choose FVSW as it can propagate in any direction along a plane uniformly, whereas the other two spin wave types (backward volume and Damon-Eshbach) can propagate in a single direction only. Since FVSW cannot be amplified by other pumping techniques such as electromagnetic pumping, we chose to use acoustic pumping. We designed and fabricated a device consisting of coplanar waveguide antennas and interdigital transducers on 1 µm thick yttrium iron garnet film. The antennas were used to both excite and detect the spin waves propagating in the device. The transducers were used to excite SAW at twice the frequency of that of spin waves – a configuration that enabled us to excite spin waves by applying the minimum acoustic power required for parametric interaction. Our experiments show that acoustic pumping generates a new counter-propagating spin wave (idler wave) with a frequency near half of the pumping frequency. The existence of the idler wave indicates that a parametric interaction was established, thereby paving the way for further investigation into amplifying the originally excited spin waves. Amplified spin waves can propagate over longer distances before getting damped. Therefore, spin-wave amplifiers can be used in magnonic circuits for signal processing and transmission applications, where signals travel as spin waves only and do! not need to convert to other forms, such as electric current.

Major Advisor: Pallavi Dhagat
Committee: Albrecht Jander
Committee: John Labram
Committee: David P. Cann
GCR: Ethan Minot