Alnico telephone receiver magnet, 1938.
© Science Museum / Science & Society Picture Library
Alnico magnets are formed through a casting or sintering proces and are composed primarily of aluminium, nickel, cobalt and iron. As well as telephone receivers, this type of magnet is found in loudspeakers, magnetos, motors and other sensing devices. Alnico has a strong resistence to corrosion, excellent stability over a broad range of temperatures and is easy to magnetise.