FOCUSING AND DEFOCUSING OF ELECTROMAGNETIC-WAVES IN A FERROMAGNET

We show that the modulation of an electromagnetic wave in a ferromagne t in the presence of an external magnetic field is governed by the non linear Schrodinger equation. We characterize the existence of an oscil latory instability of the Benjamin-Feir type for electromagnetic propa gation in a saturated ferrite. Depending on the physical parameters of the system, we establish the regions in which focusing or defocusing of the initial carrier envelope occurs. We show that one of the two pl ane waves, circularly polarized, allowed to propagate into a ferrite, is bunching into solitons and the other is modulated by a dark soliton .