What Are Coercivity and Retentivity?

Answer: The hysteresis loop gives a substance two important properties: retentivity and coercivity. Because of this, the heart of machines makes it easier to choose the right material from which to make an electromagnet.

When an external magnetizing field is used to magnetize a magnetic material, the material won’t go back to its zero-magnetism state even if the external magnetizing field is taken away.

Coercivity

The quantity of an external magnetic field with a negative sign (-ve H) that is necessary to ionize the substance is referred to as the coercivity of the substance.

Coercivity is defined as the minimal value of armature winding intensity that is required to restore the material to its initial state. This value is referred to as the coercive field.

If we take the example of a ferromagnetic substance, then when the magnetic field that is being applied is made stronger in the opposite direction, at some point Hc, the substance will entirely lose its magnetization. This stage is referred to as the coercivity stage.

Retentivity

It means that the property of a substance to retain a magnetic field even after the application or removal of an external source is referred to as its retentivity. 

It provides information about the magnetic force that the material possesses.

When the externally supplied magnetic field is reduced down to zero after the saturation point of magnetization has been reached, the amount of magnetization that is still shown by the substance is referred to as its retentivity.

Note: A hysteresis loop is one that normally consists of a closed circuit and depicts the variability of B (the induced magnetic flux density) and H (the magnetizing force). Iron is utilized in the production of electromagnets because of its high penetration resistance and low coercivity. This is because electromagnets require a material with a high retentivity but a low coercivity.