magnetic material

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One of a number of substances that are strongly attracted by magnets and can be magnetized. These include iron, nickel, and cobalt, and all those alloys that contain a proportion of these metals. Nonmagnetic materials are not attracted by magnets. These materials include paper, plastic, and rubber.

Magnetically soft materials can be magnetized very easily, but the magnetism induced in them (see magnetic induction) is only temporary. They include Stalloy, an alloy of iron with 4% silicon used to make the cores of electromagnets and transformers, and the materials used to make ‘iron’ nails and paper clips. Stroking a magnet over a steel pin from one end to the other will weakly magnetize the steel pin. This is because very large numbers of iron atoms (domains) of the steel become aligned in the same direction.

Magnetically hard materials can be permanently magnetized by a strong magnetic field. Steel and special alloys such as Alcomax, Alnico, and Ticonal, which contain various amounts of aluminium, nickel, cobalt, and copper, are used to make permanent magnets. The strongest permanent magnets are ceramic, made under high pressure and at high temperature from powders of various metal oxides. Iron is an example of a natural hard magnetic material. Its magnetic properties are due to its atomic structure. The electrons in the outer orbit of an iron atom behave as an electric charge and produce a strong magnetic field. In a magnetized piece of iron millions of individual iron atoms, called a domain, are aligned in the same direction. The domains have a north and a south pole.

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