What are permanent magnets ? What is an efficient way of preparing a permanent magnet ? Write two characteristic properties of materials which are required to select them for permanent magnets.

Explanation

Substances which at room temperature retain their ferromagnetic property for a long period of time are called "permanent magenet". An efficient way to make a permanent magnet is to place a ferromagnetic rod in a solenoid and pass a current. The magnetic field of the solenoid magnetises the rod. Materials selected for preparing permanent magnet should have
(a) high retentivity so that the magnet is a strong magnet, and
(b) high coercivity so that the magnetisation is not erased by stray magnetic fields, temperature fluctuations or minor mechanical damage.
(c) high permeability so that material becomes a strong magnet. Steel and alloys like Alnico, Cobalt steel and Ticonal are suitable materials for preparing permanent magnets.