There are essentially three main categories of magnet: permanent, temporary, and electromagnets. Permanent magnets are the most familiar form people interact with in their everyday lives. A variety of types of permanent magnet are used in domestic and industrial settings.
Extremely Strong Magnets
Neodymium iron boron magnets are composed of rare earth materials and offer a high coercive force. They are known to have a very strong magnetic attraction that is difficult to demagnetise, which enables them to be extremely small, yet effective. Neodymium magnets tend to be fragile and prone to corrosion if left uncoated. Neodymium magnets plated with iron, gold, or nickel can be used in a wide variety of applications.
Samarium cobalt magnets are strong, difficult to demagnetise, and have a high coercive force. However, they tend to be brittle. They are highly resistant to oxidation, which means that they do not usually have to be coated. They are also highly resistant to temperatures up to 300 degrees Celsius, so they are suitable for machinery where neodymium cannot withstand the exposure or heat.
Audio Equipment Magnets
Alnico magnets are used frequently in speakers and musical instrument. They are composed of aluminium, nickel, and cobalt, and are created either by sintering or casting. While sintering enhances the mechanical traits, casting creates a higher energy magnet, which can be used in more complicated designs. These magnets have excellent resistance to temperature and can be demagnetised easily.
Ceramic magnets, also called ferrite magnets, are inexpensive, not easily demagnetised, and easily produced in mass quantities. They are used to make fridge magnets, jewellery, and crafts, in addition to appearing in motors and MRI machines. Ceramic magnets are composed of sintered iron oxide and barium or strontium carbonate. They tend to be brittle, so they are ground using a diamond wheel, which enhances their strength. Ceramic magnets are available in limited shapes, most commonly, discs, blocks, and rings.