Ferrite (magnet)
Unlike many ferromagnetic materials, most ferrites are not electrically conductive, making them useful in applications like magnetic cores for transformers to suppress eddy currents.
Ferrite compounds are extremely low cost, being made mostly of iron oxide, and have excellent corrosion resistance.
Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology synthesized the first ferrite compounds in 1930.
[3] Ferrites are usually ferrimagnetic ceramic compounds derived from iron oxides, with either a body-centered cubic or hexagonal crystal structure.
They are typically composed of α-iron(III) oxide (e.g. hematite Fe2O3) with one, or more additional, metallic element oxides, usually with an approximately stochiometric formula of MO·Fe2O3 such as Fe(II) such as in the common mineral magnetite composed of Fe(II)-Fe(III)2O4.
Less often bismuth,[10] strontium, zinc as found in franklinite,[11] aluminum,yittrium, or barium ferrites are used[12][13] In addition, more complex synthetic alloys are often used for specific applications.
[14][15] Many ferrites adopt the spinel chemical structure with the formula A B2O4, where A and B represent various metal cations, one of which is usually iron (Fe).
The induced magnetic anisotropy in cobalt ferrite is also beneficial to enhance the magnetoelectric effect in composite.
[31][32] The high coercivity means the materials are very resistant to becoming demagnetized, an essential characteristic for a permanent magnet.
During the heating process, these carbonates undergo calcination: After this step, the two oxides combine to give the ferrite.
The shaping may be performed in an external magnetic field, in order to achieve a preferred orientation of the particles (anisotropy).
By matching the material and particle size to the ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading.
Ferrite particles are also used as a component of radar-absorbing materials or coatings used in stealth aircraft and in the absorption tiles lining the rooms used for electromagnetic compatibility measurements.
In particular, for hard hexaferrites today the most common uses are still as permanent magnets in refrigerator seal gaskets, microphones and loud speakers, small motors for cordless appliances and in automobile applications.
[36] Ferrite magnets find applications in electric power steering systems and automotive sensors due to their cost-effectiveness and corrosion resistance.
[39] Automotive sensors utilize ferrite magnets for accurate detection and measurement of various parameters, such as position, speed, and fluid levels.
Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology synthesized the first ferrite compounds in 1930.
The discovery was somewhat accidental—due to a mistake by an assistant who was supposed to be preparing a sample of hexagonal lanthanum ferrite for a team investigating its use as a semiconductor material.
