Parametric instability of forward volume spin waves pumped by surface acoustic waves in yttrium iron garnet films

Abstract

Parametric instabilities of forward volume spin waves pumped by a traveling surface acoustic wave (SAW) were investigated in an unpatterned yttrium iron garnet film under perpendicular magnetic bias. Conservation of momentum of the SAW enables spin wave modes with specific propagation directions to be selectively amplified from the thermal background. Devices with wavevector-selective transducers were fabricated to unambiguously detect spin waves pumped in different directions. Spin wave thickness modes at half the pump frequency were observed at distinct bias field values consistent with theory. Tilting the bias field resulted in lower instability thresholds, with linearly excited non-propagating magnons decaying into degenerate spin waves contributing to the instability in an additional pathway for energy transfer. These results establish traveling acoustic wave pumping as a method for selective excitation of spin wave modes and wavevectors for wave-based signal processing and computing applications.