Uses of Hard and Soft Magnetic Materials
Magnetic materials are classified as either hard or soft.
Soft magnetic materials are easily magnetised and demagnetised.
Hard magnetic materials are hard to magnetise, but once magnetised, they are hard to demagnetise.
Ordinary magnetics are made of hard magnetic material, since it is desired they retain their magnetism as long as possible. Until the early years of the twentieth century magnetic materials were made of steel containing between 1 % and 1.5 % carbon. It was later found that the addition of small amounts of other material – tungsten, chromium and cobalt – greatly improved the hardness of the steel. Research along the same lines led to the discovery of special alloys for making permanent magnets – alnico, alcomax and ticonal, which contain iron, nickel, cobalt and aluminium in various proportions.
Today a great range of permanent magnets of various types are used to make motors, dynamos and voltmeters, loudspeakers, ammeters, microphones. Conversely, it is often required to rapidly un - magnetise or re - magnetise a magnet. This is the case with electric door bells, relays, transformer cores. In these devices, soft magnetic materials such as mumetal (73% nickel, 22% iron, 5% copper) and stalloy (96% iron, 4%silicon) are used as well as soft iron.
Much research has also gone into sintered materials – the conversion of powdered materials into solid materials by the application of heat and pressure. Various very soft or very hard magnetic materials and some of the best permanent magnets may be made using this method.