Modification of the complex permeability of garnet and spinel ferrites by application of a static magnetic field

Abstract

The complex permeability of ferrites below 1 GHz has been investigated as a function of applied static magnetic field. Previous work by Gorter indicated that the real and imaginary parts of the permeability vary with the ratio of the magnetic ions in the structure. This paper investigates the effect of a magnetic field on the complex permeability of a spinel ferrite. The modification of the frequency dependence of the complex permeability of another spinel ferrite (magnesium-zinc) by the application of a static magnetic field was reported previously. The results of a second experiment to investigate the effect of crystalline structure on the magnetic field dependence of the complex permeability of a garnet ferrite (yttrium-aluminum) are also presented. The magnetic field effect was most pronounced in the region of domain wall rotation resonance in the VHF range (0.2–1 GHz). As in the previously reported results, permittivity did not vary significantly as a function of applied magnetic field. The wide availability of spinel and garnet ferrites with predictable properties as a function of composition should facilitate the design of devices requiring variable permeability and adjustable losses.