TITLE: Parametric Amplification of Spin Waves by Surface Acoustic Waves

ABSTRACT: Spin waves and their quanta, magnons, are a promising platform for compact low-power information processing, but their short lifetimes and propagation distances have prevented the realization of practical magnonic devices. This dissertation presents the first simulations and experiments demonstrating the parametric amplification of coherent forward volume spin waves by a surface acoustic wave (SAW). When the two waves propagate in the same direction, simulations predict that a strain of 330 ppm compensates the 3 dB of damping loss incurred during propagation. Experimental results show 5 dB gain in these conditions. If the two waves are made noncollinear, with angle of incidence 45°, the simulated threshold is reduced to 80 ppm, producing 4 dB gain experimentally. Additionally, the process generates idler spin waves that propagate in a distinct direction from both the input spin wave and SAW, introducing opportunities for signal processing and routing.

Unlike previous demonstrations of parametric pumping with electromagnetic fields, which require pulsed operation to limit the unbounded growth of thermal noise, this amplifier operates continuously; the strain threshold for signal amplification is less than the threshold for parametric instability. By adjusting the orientation and strength of the applied magnetic bias field, the device can instead be made to selectively couple with thermal oscillations, enabling controlled spin wave generation in a preferred direction. These results establish SAW-based parametric amplification and generation as a viable tool for magnonic devices and open pathways towards practical spin wave computing.

MAJOR ADVISOR: Albrecht Jander
COMMITTEE: Pallavi Dhagat
COMMITTEE: Andreas Weisshaar
COMMITTEE: Arun Natarajan
GCR: Joseph Louis