Re: Can hi-tech ceramics be made to retain magnetic polarity?

Dear Mike,

Ceramic magnets were developed in the late 1960's. These materials, usually strontium-iron oxide (SrO.6Fe₂O₃) or barium- iron oxide (BaO.nFe₂O₃), are called ferrites. They do have permanent magnetism (ferromagnetism) which is ordered, or aligned, during manufacture so as to create "poles".

Ferrite powder is pressed into the desired shape whilst in an external magnetic field. Sintering (heating to cause the individual particles to "meld" together) creates a hard, brittle magnet which can be further reduced in size by grinding, so the final size can be controlled as low as machining tolerances allow.

Some computer hard disks use ferrite coated disks because the magnetic polarity can be switched (by exposure to an external magnetic field) very quickly. Older read-write heads were also constructed of ferrites but are being replaced by smaller devices as disk capacity increases. Ferrite powder bonded to a plastic backing forms magnetic tape as used in video/audio recorders and floppy disks. The thickness of the magnetic layer is extremely small, just a few microns in most instances.

I hope that this answers your question.