Hysteresis loop or B-H curve

A B-H curve is used to show the relationship  between magnetic flux density (B)  and magnetic filed strength (H) for a material.The area of the hysteresis loop is related to the hysteresis loss.The area of hysteresis loop of a material is large, the hysteresis loss in this material will be large.Narrow hysteresis loops also have high permeability (the slope of B with respect to H) and magnetization.

                                                                 Hysteresis loop or B-H curve

Retentivity is a material's ability to retain a certain amount of residual magnetic field when the magnetizing force is removed after achieving saturation.

Coercive Force : The amount of reverse magnetic field which must be applied to a magnetic material to make the magnetic flux return to zero. 

Non retentive or soft  magnetic materials :

Soft (ferro) magnetic materials have a narrow hysteresis loop and they are easily magnetized. High saturation magnetization and a low coercivity (narrow B-H curve).Non retentive  magnetic materials  having  low magnetic losses and narrow hysteresis loop.

Retentive or hard magnetic materials :

Hard (ferro)  magnetic materials material such as cobalt steel retain their magnetism for long period of time, when  the magnetizing field is removed. i.e. They can act as a permanent magnet .Retentive or  hard  magnetic material  having high coercivity , high losses and large hysteresis loop 

Table 1 :  Narrow Vs Larger hysteresis loop area

Narrow hysteresis loop	Larger hysteresis loop
Soft (Ferro) magnetic    materials, have small coercive force	Hard (ferro) magnetic  materials have large coercive force
Lower - Retentivity,Coercivity, Reluctance, Residual Magnetism	Higher  - Retentivity,Coercivity , Reluctance, Residual Magnetism
Higher - Permeability	Lower - Permeability