Ferrite magnets are a large class of magnets that include chemical compounds such as hematite (Fe2
The first magnets that one is exposed to as a child are likely to be ferrite magnets, as they are the cheapest and most common. The stereotypical magnetic interaction one typically sees is the interaction between a ferrite magnet, usually magnetite, with iron filings. The resulting pattern that the filings are pulled into reveals the shape of the magnetic field produced by the magnet. The Earth itself produces a similar magnetic field, though trillions of times larger and about 10,000 times weaker.
Ferrite magnets, also known as ferromagnetic materials, are generally classified into two categories based on their magnetic coercivity, or persistence of internal magnetism: soft ferrites and hard ferrites. These categorizations do not refer to the actual hardness of the magnets -- both types are brittle ceramics -- but rather their magnetic coercivity. Depending on whether a magnet is soft or hard, it may have different applications. For instance, a hard ferrite magnet might be used in a radio or a hard disk. A soft ferrite magnetic would be used as a transformer core or an electromagnet core.
The strength of a ferrite magnet, like any other magnet, can be measured in teslas. One tesla represents one weber per square meter, with a weber being a unit of magnetic flux such that it would produce one volt of electricity if reduced to zero in one second. Starting with the weaker magnetic fields and moving to stronger: paramagnetic materials like aluminum or oxygen have a magnetic field of about 300 nanoteslas, the strength of the Earth's magnetic field is about 31 microteslas, the strength of a typical refrigerator magnet is about 5 milliteslas, the strength of a bar magnet is about 35 milliteslas, the strength of a loudspeaker magnet is about 1 T to 2.4 teslas, and the strength of the most powerful continuous magnetic field yet produced in a laboratory is 45 teslas.
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