Abstract: A stress stabilized ferrimagnetic material has a retained stress to provide enhanced initial permeability stability over a range of operating temperatures, such as from ?40° C. to 85° C., as well as pressures. Stress is introduced into the ferrimagnetic material, wherein subsequent processing relieves only a portion of the induced stress, and preferably less than 50% of the induced stress.

Abstract: A ferrite having a substantially continuous range of grain sizes in a substantially uniform distribution throughout the range of grain size, wherein no single grain size represents more than approximately 10% of the total grains. A method of forming a ferrite is disclosed wherein a first composition which yields a first grain size range upon sintering is combined with a second composition which yields a second different grain size range upon sintering to form a composite, and the composite is sintered to form the ferrite which exhibits a relatively temperature stable behavior within an extended temperature range.

Abstract: A process for preparing a ferrite in which a green body containing at least about 50 weight percent of iron compound is first sintered and then cooled. During the cooling cycle, from about 1,000 to about 700 degrees centigrade, the body is contacted with a reduced oxygen atmosphere containing less than 10 volume percent of oxygen. From 700 to 200 degrees centigrade, the reduced oxygen atmosphere contains less than 1 part per thousand of oxygen. Thereafter, the sintered body is treated to remove at least some sharp edges and to change its permeability; and it is then contacted with an etchant.

Abstract: A method and apparatus for establishing the magnetic permeability of a batch ferrites at a predetermined target permeability. Ferrite parts are sintered to achieve a magnetic permeability greater than the target permeability. The sintered parts are then tumbled to suppress the magnetic permeability below the target permeability. The parts are then exposed to a chemical wash to increase the magnetic permeability and continuously monitored to allow setting the magnetic permeability at the target permeability.