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Direct calculation of the electric field induced by a timevarying magnetic induction Am.Effect of a timevarying boundary on the sound field in an enclosure. I Substituting this equation into Eq. (C3) then yields an expression identical to Eq. (Cl) indicating that the solution (19) is the correct solution far from the plane z=O.The propagation of microwave magnetoelastic waves in a ferromagnet subjected to pulsed magnetic fields is investigated. In the first part of the theoretical analysis, which is restricted to spatially uniform bias fields, the interaction 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. 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, The analysis reveals that negligible coupling occurs for field gradients much smaller than the critical values, resulting in efficient magnon/phonon conversion. The critical gradients are given for both shear and longitudinal waves propagating along certain crystallographic directions. * Based on a thesis submitted to the Department of Electrical Engineering, M.LT.

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We report the first direct observation of strong Bragg-scattered infrared light (1150 nm wavelength) from coherent spin waves (1.5 GHz). The maximum scattered-light intensity is found to be at least five times stronger than that of longitudinal elastic waves of comparable power. The experiments were performed with an axially magnetized, single-crystal YIG bar, with the axis oriented in a {100} plane at an angle of 22.5° from a 〈100〉 axis. The coherent spin waves were generated through efficient space-gradient conversion from longitudinal elastic waves; the latter were excited from a sputtered ZnO transducer. The scattered-light intensity is found to be dependent on the incident-light polarization and the sign of frequency shift (Stokes or anti-Stokes lines) and independent of the direction of the applied magnetic field. Previous theoretical calculations on light scattering from coherent spin waves are critically reviewed and revised. The new result appears to explain adequately not only the present experiments but also observations that previous authors have reported as ``anomalous''.

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