Ferrites in Microwave Applications

The ferromagnetic Faraday effect occurs at microwave frequencies as a direct result of the dispersion in permeability which is associated with ferromagnetic resonance. The resonance can be explained most simply by stating that the total magnetization vector of a magnetized ferromagnetic material has associated with it an angular momentum arising from the angular momenta of all of the spinning electrons contributing to the magnetization. Because of this angular momentum (which is directed along the same axis as is the magnetic moment but in the opposite direction) the magnetization vector behaves as a top or gyroscope. If it is displaced from its equilibrium position in a steady magnetic field it will not rotate directly into alignment with the field but will precess about the dc field direction at a frequency determined by the strength of the'dc field. In the absence of damping this precession would continue indefinitely, but damping losses are such that the precession will damp out in approximately 10 -s sec. * C. L. H o g a n , T h e Ferromagnetic F a r a d a y Effect at M i c r o w a v e Frequencies and I t s Applications -- T h e Microwave Gyrator, R . S . T . J . , 31, pp. 1-31, Jan., 1952. 1333