Domain wall motion induced by strong microwave fields

A new high power effect in ferrites, the motion of domain walls induced by microwave pulses is described. In high power phase shifters using ferrite toroids this effect can change the remanent magnetization and hence change the insertion phase of the device. A theoretical explanation of these effects is obtained by considering a partially magnetized ferrite material having uniaxial anisotropy and exposed to an rf magnetic field perpendicular to the anisotropy axis. Experiments at 3 GHz on a twin-slab (i.e., toroid) phase shifter at peak power levels up to 300 kW are in good agreement with the theoretical expectations. It is shown that a circularly polarized rf magnetic field of strength hoexerts substantially the same pressure on domain walls as a dc magnetic field applied along the domain axis and having the strength w, where γ is the gyromagnetic ratio and ω the angular frequency. The rf generated pressure tends to shrink those domains in which the imposed sense of circular polarization coincides with the sense of the natural spin precession.