Permanent Magnets

Permanent magnets are objects made from material that is magnetized by an external magnetic field. Once they have been magnetized, permanent magnets are able to retain their magnetism indefinitely even after removing them from the external magnetic field.

In some instances, permanent magnets can be demagnetized through a certain type of electric current or through exposure to very high temperatures, but most permanent magnets are difficult to demagnetize.

Types of permanent magnets:

Neodymium Magnets, also known as Rare Earth magnets, are made of Neodymium (Nd), Iron (Fe), and Boron (B). Neodymium magnets offer the strongest magnetism commercially available and are unexpectedly strong for their size. They are the strongest of the permanent magnets, but the least resistant to corrosion. Most neodymium magnets are usually coated with nickel, gold, or iron. The strength of neodymium magnets varies according to their Grade. Higher grade numbers indicate a more powerful magnets. For example, a grade N52 neodymium magnet has a stronger pull force than a grade N40 magnet. Letters after the Grade, for example N42SH, refer to heat tolerance.

Samarium Cobalt magnets are made of Samarium (Sm) and Cobalt (Co). These are also considered Rare Earth magnets. This type of permanent magnet is similar to the NdFeB magnets in the sense that they have a strong pull force; however SmCo magnets have higher resistance to heat and therefore operate more reliably in high temperature applications, such as motors.

Ceramic magnets, also known as Ferrite magnets, are made from a composite of iron oxide and barium carbonate or strontium carbonate. These permanent magnets are quite brittle but very resistant to corrosion and are not easy to demagnetize. Ceramic ferrite magnets are inexpensive and are widely used, although Neodymium magnets are now also very popular.

Alnico magnets are made of Aluminum (Al), Nickel (Ni), and Cobalt (Co), hence the name Al-Ni-Co. Alnico permanent magnets are preferred for many applications because they are very stable over a wide range of temperatures, as well as being resistant to corrosion. The familiar horseshoe magnets are made of Alnico.