Ferrite History

The first type of magnetic material known to man was in the form of lodestone, consisting of the ore magnetite (Fe2O3). This is believed to have been discovered in ancient Greece around the time period of 800 BC. Magnets found their first application in compasses, which were used in the nineth century by the Vikings, or perhaps even earlier.

A milestone in the history of magnetism was the work done by William Gilbert in 1600. His work "De Magnete, Magneticisque Corporibus, et de Magno Tellure" described the magnetic properties of lodestone up to that point in time.

It was not until two hundred years later that major developments began to occur. These developments included work done by Hans Christian Orsted, Andre Marie Ampere, Wilhelm Eduard Weber, Michael Faraday, Pierre Curie, and James Cleck Maxwell. Their work provided the basis of electromagnetic theory in general and for crystal structures.

In 1947, J.L. Snoeck published the book, New Developments in Ferromagnetic Materials. Studies done by Snoeck and others at Phillips Laboratories in the Netherlands led to magnetic ceramics with strong magnetic properties, high electrical resistively, and low relaxation losses.

At about the same time, in 1948, L. Neel announced his celebrated theoretical contribution on ferrimagnetism. This dealt with the basic phenomenon of "spin-spin interaction" taking place in the magnetic sublattices in ferrites. The stage was now set for the development of microwave ferrite devices.

In 1952, C. L. Hogan from Bell Labs made the first non-reciprocal microwave devise at 9 GHz that was based on the Faraday rotation effect. Research was completed to improve the properties of the spinel ferrite materials by various cation substitutions. This modified the magnetic properties for different frequency ranges, power requirements, and phase shift applications.

In 1956, Neel, Bertaut, Forrat, and Pauthenet discovered the garnet ferrite class of materials. This type of ferrite material has three sub lattices, and is also referred to as rare-earth iron garnets. These materials, although having a magnetization lower than spinel ferrite, possess extremely low ferromagnetic line width.

Another class of ferrite material that was developed during this time is the hexagonal ferrite. These materials have three basic sub lattices combined in different numbers in a hexagonal structure. The high anisotropy fields have been utilized in microwave ferrite devices in the millimeter range.

In 1959, J.Smit and H.P.J. Wijn published a comprehensive book on ferrite materials entitled Ferrite.

Developments have been made on the magnetic characteristics of ferrite materials since the 1950s that have improved microwave device performances. These involve both compositional and processing modifications. New application of ferrite materials continue to be realized, such as in the cellular phone, medical, and automotive markets.

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