Explain qualitatively on the basis of domain picture the lireversibility in the magnetisation curve of a ferromagnet.

Explanation

(a) When a ferromagnetic substance is subjected to external uniform magnetic field, magnetic dipole moment in each domain tends to align, parallel to magnetic field because of torque exerted on it. Some energy is spent for doing this work out of which some part is stored in the dipoles in the form of magnetostatic potential energy and remaining part is wasted in the form of heat (which is called hysterisis loss). Now, though magnetic field is removed organised orientation of all the dipoles remain unchanged. They do not come back to their random orientations (because in the absence of magnetic field, no torque is exerted on the dipoles to change their orientations). Thus, magnetising process is irreversible.