Sustained Amplification of Coherent Spin Waves by Parametric Pumping with Surface Acoustic Waves

Parametric amplification offers a route to overcoming intrinsic damping in spin-wave systems, a key challenge in the development of magnonic signal processing and computing technologies. Here we demonstrate the sustained amplification of coherent forward volume magnetostatic spin waves in a yttrium-iron-garnet thin film using a traveling surface acoustic wave as a nonstationary pump. A gain of up to 6 dB is achieved under continuous pumping below the threshold for parametric instability. The interaction generates an idler wave at a distinct frequency, consistent with three-wave mixing governed by energy and momentum conservation. This approach enables stable, frequency- and wavevector-selective spin-wave gain using practical pump power levels, establishing acoustic wave pumping as a viable mechanism for realizing active components in integrated magnonic circuits.