Alnico facts for kids
Alnico alloys are ferromagnetic (a mechanism by which some materials form permanent magnets). Alnico alloys also have a high coercivity (they do not easily lose their magnetism) and are used to make permanent magnets. Before rare-earth magnets were developed in the 1970s, alnico magnets were the strongest type of magnet. The development of Alnico began when T. Mishima in Japan found that an alloy of iron, nickel, and aluminium had double the coercivity of the best magnets of that time. (the coercivity of Alnico is 400 oersted).
Alnico alloys can be made magnets by strong magnetic fields. Rare-earth magnets like neodymium and samarium-cobalt are the only easily found magnets which are stronger than alnico magnets. Alnico magnets produce very strong magnetic fields at their poles (a pole is one of the two ends of a magnet) as high as 1500 gauss (0.15 tesla which is about 3000 times stronger than earth's magnetic field.
Some types of alnico magnets are isotropic (properties are same in all directions) and can be properly magnetised in all directions. Other types like alnico 5 and alnico 8 are anisotropic (properties change when direction changes) have a preferred direction (one direction would be better than other directions) for magnetisation. Anisotropic alnico alloys will make stronger magnets in their preferred direction than an isotropic alnico alloy.
Alnico magnets are the only magnets that have useful magnetism even when heated red-hot.
In 2008, the cost of Alnico magnets was about $44/kg ($20/pound).
Images for kids
Alnico 5 magnet used in a magnetron tube in an early microwave oven. About 3 in (8 cm) long.
Advertisement by Jensen Radio Manufacturing Co. for Alnico 5 loudspeakers in 1945. As illustrated, Alnico 5 allowed a dramatic reduction in size and weight of magnet needed to produce a given flux, from 90 oz in 1930 to 4.6 oz.
Alnico Facts for Kids. Kiddle Encyclopedia.