Abstract
The parallel-pumped spin-wave instability (SWI) threshold power, P_{\mathrm{th}} , of polycrystalline yttrium iron garnet (YIG) excited by microwave pulses with the varied rising-edge time was investigated theoretically and experimentally. The SWI threshold model associated with the rising-edge time t_{r} is developed in terms of the attributes of half-frequency spin waves in the applied static fields H_{\mathrm{ext}} . The results manifest a significant increase in microwave-excited SWI threshold power level when the rising-edge time t_{r} is shortened from 600 to 100 ns at the X-band. In addition, the rising-edge microwave pulses with different time scale distinctly present different threshold responses under the left-wing field region of the butterfly curves. The SWI thresholds associated with the spin-wave initial amplitude grow with increasing H_{\mathrm{ext}} when t_{r} is smaller than the spin-wave relaxation time ( t_{r} \bm{\le} 200 ns), while SWI thresholds are more sensitive to the k -dependent spin-wave linewidth, which decreases with the increasing H_{\mathrm{ext}} as t_{r} exceeds the spin-wave relaxation time ( t_{r} \bm{\ge} 400 ns). The calculated responses of the SWI threshold are in close agreement with the measurements.