Explain Hysteresis loop.

Hysteresis loop: In a ferromagnetic material, the flux density B raises while external applied magnetic field H to it is raised. When the saturation gets, the raise in flux ceases even though H may be raised. This has been demonstrated by OS in the figure. If the external field is slowly reduced, the original curves OS is not retraced although follows curve SR. The external field H is decreased to zero but B does not reduce to zero that is the material keeps magnetised. The value of R flux density is termed as remanent flux density or residual magnetism. So as to demagnetise the material completely, external magnetic field must be reversed and while this reaches the value OC in reverse direction, this is seen that B is zero. This applied reverse magnetising force that causes B to become zero is termed as coercive force. Additional increase of H in reverse direction will now rise in B in reverse direction and again at the point S saturation arises. The residual magnetism in reverse direction is represented through OR and to neutralise this H should be increased in positive direction to the value OC. Additional increase in H will again magnetise the material and saturation will arise at S. The characteristic of magnetic behaviour of the ferromagnetic material is above in property. When the material is taken by one complete cycle of magnetisation, this traces a loop termed as hysteresis loop. While a material is subjected to cyclic changes of magnetisation, the domains modify the direction of their orientation in accordance along with H. Work is completed in changing the direction of domains, that leads to production of heat in the material. The energy needed to take the material by one complete cycle of magnetisation is proportional to the area enclosed through the loop.

Hysteresis loop