Reverse Doppler effect in backward spin waves scattered on acoustic waves

摘要

We report on the observation of reverse Doppler effect in backward spin wavesreflected off of surface acoustic waves. The spin waves are excited in ayttrium iron garnet (YIG) film. Simultaneously, acoustic waves are alsogenerated. The strain induced by the acoustic waves in the magnetostrictive YIGfilm results in the periodic modulation of the magnetic anisotropy in the film.Thus, in effect, a travelling Bragg grating for the spin waves is produced. Thebackward spin waves reflecting off of this grating exhibit a reverse Dopplershift: shifting down rather than up in frequency when reflecting off of anapproaching acoustic wave. Similarly, the spin waves are shifted up infrequency when reflecting from receding acoustic waves.