The interaction between magnetic waves in a ferrite and drifting charges in a semiconductor is studied for flat geometries (slabs or plane surfaces), in view of identifying a possible amplification mechanism. This is done through an energetic formulation which gives the imaginary part of the wave propagation constant. Results are derived both for the transverse and the longitudinal magnetization and show that high gain values are theoretically possible. Along the way, the following interesting results have also been obtained: (i) the electromagnetic fields in the absence of interacting charges ("cold" fields) have been obtained for the surface magnetic wave (transverse propagation) together with the dispersion curve; (ii) the correct expressions of the rf fields have been calculated for the slab, both for the transverse and the longitudinal propagation.

The problem of the amplification of surface magnetic waves in transversely magnetized ferrite slabs has been solved in a general planar layered structure. It is found that the amplification indeed exists, but it is confined to a definite (very narrow) frequency range, which depends essentially on the drift velocity of the interacting charge carriers. The amplification depends in a fundamental way on semiconductor conductivity, and also on the magnetic losses of the ferrite. The above results are deemed to constitute all the essential characteristics of the amplification phenomenon. Complex-wave-number magnetostatic (ms) modes in the transversely magnetized slab are also found that complete the already-known real-wave-number ms surface wave. Consideration of these modes is required when performing the exact analysis of the amplification process by numerical computation.