Computer Study of Transient Spin-Wave Buildup in Ferrites

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Abstract
The equations of motion for spin waves in a spherical ferrite sample, together with equations for the uniform mode, have been programmed on a digital computer. The equations for the uniform mode are general and allow for arbitrary amplitude of the mode. The spin-wave equations are solved to first order in the spin-wave amplitudes, so that the parametric couplings which lead to first-order and second-order spin-wave instabilities are included. These equations have been solved for the case of transient buildup of the uniform mode in a magnetic field whose amplitude rises linearly with time. With rapidly rising fields, it is found that the uniform mode attains amplitudes far exceeding the limits of the usual small-signal analysis. The parametric buildup of spin waves accompanying the uniform mode is traced as a function of time, and the effect of these spin waves upon the uniform mode is considered. This defines the conditions under which useful transient devices can be designed for the generation of microwave energy with pulsed magnetic fields, which can take advantage of the large rf magnetization in ferrites when operated well beyond the usual steady-state saturation limits.

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