0.22 Chapter 7. section 7.6.3. hysteresis loops of hard iron and

Chapter 7. Section 7.6.3. Hysteresis Loops of Hard Iron and Soft Iron.

Figures are at the end of the module

In Figure 7.18. given in the previous module, the magnetization curves of Ferromagnetic materials, Paramagnetic Materials and Diamagnetic Materials are given. Para or Diamagnetic materials have linear magnetization curve hence there are no hysteresis loops and Ferromagnetic Materials have non-linear curves hence they have hysteresis loops. Hysteresis loop implies hysteresis loss.

This means in magnetizing or demagnetizing a ferromagnetic material, some energy is expended. The energy expended will depend on the ease with which we can magnetize a ferromagnetic material.

Soft irons are used in electro-mechanical relay switches as shown in Figure 7.19. An actuating current easily magnetizes the soft iron core and attracts the spring-loaded switch. In this process the electro-mechanical relay is closed. As the current is turned off the switch is immediately opened by spring action. The hysteresis loop of Soft Iron along side the hysteresis loop Hard Iron is shown in Figure 7.20.

As seen in Figure 7.20, soft iron has a much higher saturation Magnetization (B _S2 ) but hard iron has a much higher remnant Magnetization (B _r ) as well as a much higher Coercive Magnetic Field(H _C ).

Soft iron gives rise to temporary magnet whereas hard iron gives a permanent magnet. Because of high remnant Magnetization as well as a much higher Coercive Magnetic Field that hard iron becomes a permanent magnet.

Section 7.7. Theoretical basis of spontaneous Magnetization in Ferromagnets.

The theoretical basis of magnetism is the Orbital Angular Momentum of the orbital electrons in an atom and the Spin Angular Momentum of the spinning electron circulating around the nucleus of the atom.

Just as our Earth has orbital period of 365.25 days around the Sun but it has a spin period of 24 hours around it spin axis. In a similar fashion orbital electrons have orbital angular momentum J _L as well as it has J _S spin angular momentum.

Both these angular momentums give rise to dipole moments. Their parallel alignment can give rise to strong spontaneous magnetization as we find in magnetic materials such as FERRO-MAGNETIC Materials.

Their random alignment can give rise to weak spontaneous magnetization as we find in PARAMAGNETIC materials. Diamagnetic materials have no magnetization.

In 1915, Albert Einstein in team with W.J. de Hass (the son-in-law of the great Dutch physicist H.A.Lorentz) demonstrated that magnetism was a result of the alignments of electron’s orbital magnetic moment and spin magnetic moment. As shown in Figure 7.21. they attached a soft iron cylinder from a friction less pivot. The soft iron was surrounded by solenoid. Whenever a impulsive current was passed through the solenoid, the soft iron got magnetized and experienced a rotary motion so as to keep the overall Angular momentum equal to zero.