Magnetoelastic and Magnetostatic Waves in Time-Varying Magnetic Fields

摘要

The propagation of microwave magnetoelastic and magnetostatic waves in a ferromagnet subjected to pulsed magnetic fields is investigated both theoretically and experimentally. In the first part of the theoretical analysis, which is restricted to spatially uniform bias fields, the coupling between the magnetic and elastic systems is neglected. Using a coupled mode approach, it is found that plane spin waves propagate in magnetic field transients with negligible reflections, constant momentum and wavenumber, but variable frequency and power flow. These results are further elucidated by the study of a simple step transient case. The analysis is also extended to magnetostatic modes propagating in axially magnetized cylinders. In the presence of magnetoelastic interaction, the theory indicates that besides changes in frequency and in power flow, the field gradient causes group velocity modulation and changes in the time duration of wave packets. In addition there is an exchange of momentum between the different branches of the dispersion relation; this exchange is calculated in terms of critical field gradients. These critical gradients are given for both shear and longitudinal waves propagating along certain crystallographic directions. Experiments with magnetoelastic pulses in axially magnetized YIG rods confirm the theoretical predictions. (Author)