Hard ferrite (ceramic) magnets were developed in the 1960's as a low cost alternative to metallic magnets. Even though they exhibit low energy (compared with other permanent magnet materials) and are relatively brittle and hard, ferrite magnets have won wide acceptance due to their good resistance to demagnetization, excellent corrosion resistance and low price per pound. In fact, measured by weight, ferrite represents more than 75 percent of the world magnet consumption. It is the first choice for most types of DC motors, magnetic separators, magnetic resonance imaging and automotive sensors.

GENERAL CHARACTERISTICS
Hard ferrite magnets are manufactured to rigid magnetic and physical standards which normally exceed Magnetic Materials Producers Association (MMPA) standards.

The chemical composition is SrO-6(Fe₂O₃), strontium hexaferrite. The raw materials used to produce ferrite magnets are strontium carbonate and iron oxide both of which are readily available and low in cost. As a result, the use of ferrite magnets in most applications is more economical than other materials.

Ferrite magnets are formed by compaction in dedicated, multi-cavity dies followed by sintering in high temperature furnaces. This produces a hard, brittle part that requires diamond wheels for grinding to close tolerances. While physically quite strong, these magnets should not be considered a structural member in an assembly. And like most ceramics, they are brittle and should be handled so as to avoid chipping and cracking.
 
TEMPERATURE EFFECTS
Temperature variation can result in both reversible and irreversible changes in magnetization. A reversible change occurs at the rate of approximately -0.2% per degree centigrade. That is, as temperature rises above ambient, induction (Br) will decrease. Coercivity, a measure of resistance to demagnetization, changes at a rate of about 0.27% per degree centigrade. As temperature rises, a ferrite magnet will increase in coercivity!

Irreversible changes can result from exposure to very low temperatures, and the magnetic quality is restored only by re-magnetization. Irreversible changes can be avoided by providing an adequate permanence coefficient.