Permanent Magnets History in the Aspect of Magnet Energy
– Energy Product (BH)max is a measure of magnet strength,
which has the unit of MGOe (CGS system) or kJ/m3 (SI system). 1 MGOe = 7.958 kJ/m3
The modern permanent magnets (PM) history started about 1940 when Alnico was introduced. Alnico is an acronym referring to a family of iron alloy with aluminium (Al), nickel (Ni) and cobalt (Co). They also include Cu, and sometimes Ti. Before this, the use of permanent magnets was limited to a few applications such as the compass. With the introduction of Alnico, it became possible to replace electromagnets with permanent magnets and the use of magnets started to become widespread devices such as loudspeakers, electric motors, electric guitar pickups, microphones, sensors, traveling wave tubes, and cow magnets. Alnico magnets have energy product up to 13 MGOe.
In 1950’s, the penetration of permanent magnets into our everyday life gathered momentum with the discovery of ferrite ceramic magnets by scientists at Philips Laboratories. The ferrites are magnetic iron oxides with a hexagonal structure, formed by iron, oxygen and at least one other metallic element, usually Bbarium or strontium and often contain other metals such as cobalt as well. with their low cost, high coercivity, ferrites are the major global magnetic material by volume, being widely used in small electric motor and many others, with over 400,000 tonnes of hexagonal ferrites produced in 2012 . Ferrites have energy product up to 5.5 MGOe.
A revolution in PM materials started about 1970 with the introduction of the samarium-cobalt Sm-Co rare earth family with the magnet energy up to 33 MGOe. This revolution was accelerated with the discovery of neodymium, iron and boron Nd-Fe-B magnets in 1983, which now have energy product up to 52 MGOe for large scale commercial available products. These two families of rare-earth magnets have such high energy densities that they can not only replace electromagnets, but also have applications not available to electromagnets. (read the REPM history in the next page)