Nondegenerate Parametric Pumping of Spin Waves by Acoustic Waves

The linear and nonlinear interactions between spin waves (magnons) and acoustic waves (phonons) in magnetostrictive materials provide an exciting opportunity for realizing novel microwave signal processing devices and spintronic circuits. Here, we demonstrate the parametric pumping of spin waves by acoustic waves in a ferrimagnet, the possibility of which has long been theoretically anticipated but never experimentally realized. Spin waves propagating in a thin film of yttrium iron garnet-a magnetostrictive ferrimagnet with low spin and acoustic wave damping-are pumped using an acoustic resonator driven at frequencies near twice the spin wave frequency. The observation of a counterpropagating idler wave and a distinct pump threshold that increases quadratically with frequency nondegeneracy are evidence of a nonlinear parametric pumping process consistent with classical theory. This demonstration of acoustic parametric pumping lays the groundwork for developing new spintronic and microwave signal processing devices based on amplification and manipulation of spin waves by efficient, spatially localized acoustic transducers.