High Performance Magnets

A big step in the evolution of the permanent magnet materials used today came in the 1930’s with the development of Alnico magnets. In 1931, T. Mishima discovered that an alloy of iron, nickel, aluminum had a much higher coercivity than the best steel magnets of the time. Further research created alnico, a term referring to a series of permanent magnet alloys which in addition to iron are composed primarily of aluminum (Al), nickel (Ni) and cobalt (Co). Various alnico grades with differing magnetic properties can be achieved by modifying the chemistry and manufacturing process. Today’s composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, with the balance being Fe. In addition to varying the alloy composition, specialized casting techniques can be used to achieve unique crystalline grain orientation. Examples of this are alnico 5-7 and 9. Once magnetized, Alnico magnets have between 5 and 17 times the magnetic force of magnetite or lodestone, a naturally occurring magnet which can attract iron.

Alnico magnets have the benefit of having the lowest temperature coefficient, or temperature stability of all of the permanent magnet materials. Plus, they can be calibrated and have high residual induction.Before the development of rare earth magnets in the 1970’s, alnico was the strongest type of permanent magnet. Since that time, many applications using alnico have replaced it with less expensive or more powerful types of magnets. However, the fact that alnico can be used in very high temperatures (up to 930°F or 500°C) make them indispensable in certain applications. Alnico magnets are also ideal for corrosive applications and are commonly used for various types of sensors. They are stronger than ceramic magnets, but not as strong as rare-earth magnets.