Propagation of spin wave under time dependent magnetic fields

The spin-wave dispersion relation strongly depends on the effective magnetic field acting on the magnetic moments. In order to investigate how spin waves behave if the magnetic field changes in time during their propagation, we applied pulsed magnetic fields changing on the nanosecond time scale.
Spin waves were excited in a NiFe micro stripe. A static bias magnetic field and a time dependent pulse field were applied to the stripe. The spin-wave intensity was measured by time-resolved Brillouin light scattering microscopy. We observed a frequency shift of spin waves at the rising edge of the pulse field. The change in frequency can be understood by the shift of the dispersion relation induced by the pulse field. We succeeded to manipulate the spin-wave frequency during their propagation by temporally inhomogeneous magnetic fields.