The effect of an applied magnetic field on the complex permeability of a hexagonal ferrite

The complex permeabilities of ferrites with spinel, garnet, and hexagonal crystal structure have been measured as a function of frequency and applied magnetic field. A simple phenomenological theory derived from J.F. Snoek's (1948) limit concept has been applied as a guide to the behavior of these ferrites as controllable magnetic materials. The crystal structure has not proved to be a good predictor of permeability dependence on applied magnetic fields. Rotational resonance and significant cubic anisotropy are useful indicators of controllable behavior. The existence of substantially modifiable magnetic materials such as barium ferrite and YIG that exhibit control behavior suggests the feasibility of molecular design of materials in the 100-MHz to 3-GHz frequency range.>