Hysteresis: The phenomenon of lagging of magnetic induction behind the magnetizing field is called Hysteresis and called “delayed”.

ob:- Residual magnetism.

The property is known as retentivity & the extent of magnetism ob is known as Residual magnetism.

Coercivity (x) is the measure of that external magnetic field which is required to destroy the residual magnetism. It is also known as magnetic hardness of substance.

This is known as memory of magnetic field. More the retentivity, stronger the magnet more the coercivity better for making permanent magnets.

Energy supplied for hysteresis and dehysteresis is proportional to the area covered by the graph.

Soft iron has large retentivity and small coercivity where steel has larger coercivity and small retentivity.

Substances with large coercivity are suitable to make permanent magnets.

Certain alloys like alnico have large coercibity as well as retentivity. They make strong permanent magnets.

Starting from point a on the graph & reaching back while moving through points bcdef completes one cycle of hysteresis. The energy required to take a sample once through a complete cycle of hysteresis is proportional to area enclosed is Hysteresis loop.

Coercivity  Permanent magnet

Retentivity Stronger the magnet.