Ferrite magnets are ceramics that attract ferromagnetic materials and other magnets. They are the simplest and cheapest type of magnet, with two categories: soft and hard. Their strength is measured in tesla, with the strongest being 45 tesla in a laboratory.
Ferrite magnets are a large class of magnets that include chemical compounds such as hematite (Fe23) and magnetite (Fe3O4), which is the most naturally occurring magnetic mineral on Earth. They are ceramics and magnets, meaning they attract other ferromagnetic materials and either attract or repel other magnets. A ferrite magnet is the simplest type of magnet, as opposed to more sophisticated magnets such as Alnico magnets or neodymium magnets (rare earth magnets). They are also permanent magnets, unlike electromagnets, which are magnetic only when energized with electricity.
The first magnets people are exposed to are usually ferrite magnets, as they are the cheapest and most common. Children are often given toys made of iron filings that can be moved around with this type of magnet, usually lodestone. If the magnet is placed on the filings, the resulting pattern in which they are drawn reveals the shape of the magnetic field. The Earth itself produces a similar magnetic field, albeit 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 ratings do not refer to the actual hardness of the magnets – both types are brittle ceramics – but rather to their coercive strength. Depending on whether a magnet is soft or hard, it can have different applications. For example, a hard magnet might be used in a radio or hard drive, while a soft one might be used as a transformer core or electromagnet core.
The strength of a ferrite magnet, like any other magnet, can be measured in tesla. A tesla represents one weber per square metre, 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. Here are some examples, starting with the weakest magnetic fields and working your way up to the strongest:
Paramagnetic materials such as aluminum or oxygen have a magnetic field of about 300 nanotesla.
The Earth’s magnetic field has a strength of about 31 microtesla.
The strength of a typical refrigerator magnet is about 5 millitesla.
A bar magnet is about 35 millitesla.
A speaker magnet has a strength of about 1 T to 2.4 tesla.
The strength of the strongest continuous magnetic field ever produced in a laboratory is 45 tesla.
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