Domain theory of magnetism.

Domain theory of magnetism.

In ferromagnetic substances dipoles (small atomic magnets) form large groups called domains. These dipoles face one direction where the direction varies from one domain to another. In an un-magnetized material, dipoles in different domains face in different directions hence their resultant magnetism is zero.

When a magnetic material is placed in a magnetic field the dipoles get aligned and eventually all domains face the same direction. When this happens then the material becomes magnetized. When a material is fully magnetized we say it is saturated. This means that the magnetism of the material cannot be increased by any other method.

Hard and soft magnetic materials

Hard magnetic materials that that are difficult to magnetize but retains magnetism for long. Such materials are used to make permanent magnets. Steel is an example.

Soft magnetic materials are those that are easily magnetized but do not retain magnetism for long. Such materials are to make temporary magnets. An example is iron.