What materials should be used to make permanent magnets ?

Explanation

The hysteresis curve allows us to select suitable materials for permanent magnets.
The material should have high retentivity so that the magnet is strong.
These material have high coercivity, so that the magnetization is not erased by stray magnetic fields, temperature fluctuations or minor mechanical damage.
Steel is one favoured choice. It has a smaller retentivity than soft iron but has much smaller coercivity of soft iron.
Other suitable materials for permanent magnets are alnico, cobalt steel and ticonal.