Impact of Spin-Wave Dispersion on Surface-Acoustic-Wave Velocity

The dependence of the velocity of surface acoustic waves (SAWs) as a function of an external applied magnetic field is investigated in a Fe thin film epitaxially grown on a piezoelectric GaAs substrate. The SAW velocity is observed to strongly depend on both the amplitude and direction of the magnetic field. To interpret the experimental data a phenomenological approach to the relative change in SAW velocity is implemented. We find that the experimental velocity variation can be well reproduced provided that the spin-wave dispersion is taken into account. The validity of this phenomenological model is attested by the comparison with a fully magnetoelastic one. Nonreciprocity of SAW velocity is also addressed both experimentally and theoretically.