1.Introduction: THE basic discovery that ferrites could be used as permanent magnets was made by Kato and Takei some thirty years ago. However, these early ferrite magnets had little practical significance and lot of improvements was made in the recent years.
Permanent magnets are the basis of an ever increasing number of devices of modern life. The development of permanent magnets during this century has shown a continuous increase of quality, strength and the ability to store energy, characterized by the so-called energy product (B • H)max .
The most important oxide used in permanent magnets is Ba-hexaferrite (BaFe12O19) and related compositions. Discovered in 1950 in the Philips laboratories, these materials revolutionized the use of permanent magnets in everyday life. An overview of ferrite magnets can be found in the literature (e.g. McCurrie 1994). The…show more content… Their general chemical formula may be written as AB2O4, where A and B represent different metal cations. Ferrites are, like most of the other ceramics, hard and brittle. They are both electrically nonconductive and ferrimagnetic, meaning they can be magnetized or attracted to a magnet. Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology synthesized the first ferrite compounds in 1930.
2.Types OF Ferrite Magnets:
2.1 Structure and Composition:
Ferrites are hard and brittle in nature like ceramics. Most number of ferrites are spinels, They have a crystal pattern composed of cubic close-packed (FCC) oxides (O2-) They are formulates as ABO, in which A and B are different metal cations , mainly consist of iron Fe. In Spinel ferrites , A cations holding one 1/8 of the tetrahedal sites and B cations holding 1/2 of the octahedral sites.
2.2 Spinel ferrites: These may be:
• Normal Spinel Ferrites
• Inverse Spinel Ferrites
• Mixed Spinal