At this point, it can be seen that some magnetic flux remains in the material even at zero magnetic field. This is called as RETENTIVITY and indicates the remnance or level of residual magnetism in the material. As the magnetic field is reversed, the curve moves to point 'c', where the magnetization reaches to zero. This point is called as COERCIVITY or coercive force. On further increasing the field in the negative direction, the materials become magnetically saturated but in the opposite direction (point 'd'). Reducing the field to zero brings the curve to point 'e'. At this point, the level of residual magnetism is almost equal to that achieved in the other direction (point 'b'). Increasing the field back in the positive direction returns the magnetization to zero. subsequently, the curve takes a different path from point 'f' back to the saturation point (point 'a') where it completes the loop.

From the M-H loop, a number of primary magnetic parameters of a magnetic material can be determined.
[1]. Retentivity: A measure of the residual flux density corresponding to the saturation induction of a magnetic material. In other words, it is a material's ability to retain a certain amount of magnetization when the magnetizing field is removed after achieving saturation.
[2]. Residual Magnetism or Residual Flux: The magnetic flux density that remains in a material when the magnetic field is zero. Note that residual magnetism and retentivity are the same when the material has been magnetized to the saturation point. However, the level of residual magnetism may be lower than the retentivity value if the magnetic field did not reach the saturation level.
[3]. Coercive Force: The amount of reverse magnetic field which must be applied to a magnetic material to make the magnetization to zero.
[4]. Permeability: A property of a material that describes the ease with which a magnetic flux is established in the component.

These hysteresis parameters are not solely intrinsic properties but are dependent on various parameters such as grain size, domain state, internal stresses, and temperature. Because the hysteresis parameters are dependent on grain size, they are useful for magnetic grain sizing of natural samples. The elements Fe, Ni, and Co and their alloys are typical examples of FM materials.

4. Ferrimagnetism:

More complex form of magnetic ordering can occur in some magnetic materials as a result of crystal structure: One such magnetic ordering is called ferrimagnetism (FiM). A simple representation of the magnetic spins in a FiM is shown in Figure 1.5. One can consider the arrangement as two interpenetrating sub-lattices, one with the up spin and the other with the down spin with magnetization M_↑ and M_↓, respectively. In FiM, the magnetic moments of the different sublattices are not equal and result in a net magnetic moment. Therefore, FiM is similar to a FM. It exhibits all the hallmarks of FM behavior: spontaneous magnetization, Curie temperature, hysteresis, and remnance. However, FM and FiMs have very different magnetic ordering.