FerroMagnetic Substances

The generation of the magnetic field in the matter contributes to the spinning motion of the electrons and their interactions. The response of different materials to magnetism forms the basis of the classification of matter into paramagnetic, diamagnetic and ferromagnetic. All materials have some magnetic permeability, some have higher and some have lower. When kept in a strong external magnetic field, the substances that form permanent solid magnets are ferromagnetic. The reason stated for this particular property is the presence of small regions known as the solid-state domains into which the metal ions are grouped. These domains are randomly oriented and cancel out each other’s magnetic fields. In the presence of an external electric field, the domains get oriented in the direction of the applied field and thus generate a strong magnetic effect. The permanent nature of this magnetism contributed to the change in the orientation of these domains permanently.

Properties Of Ferromagnetic Substances

1. The atomic dipoles of ferromagnetic substances have the same orientation as the external magnetic field.

2. There is a permanent dipole moment present in the ferromagnetic substances’ atoms that lie in their domain.

3. The magnetization intensity is significant, positive and proportional to the magnetizing field. The saturation of the magnetization varies from material to material.

4. The dipole moment of the ferromagnetic substances is huge and is in the same direction as the magnetizing field.

5. The magnetic flux of the ferromagnetic substance is considerable and positive as the field lines inside the material are very dense. Magnetic flux can be calculated as B =μ₀ (H+M)

 μ₀ = magnetic permittivity of free space

 H = strength of the applied magnetic field

 M = intensity of magnetization

6. The magnetic susceptibility of ferromagnetic materials is also significant and positive, which can be calculated by X_m= M / H

 M = intensity of magnetization

 H = strength of the applied magnetic field

7. On liquidation, the ferromagnetic substances lose their magnetic properties due to exposure to high temperatures.

8. The relative permeability of a ferromagnetic substance is also significant and proportional to the magnetizing field present inside the material.

9. The magnetizing field inside the material is more potent than the field applied.

10. As the ferromagnetic substances generate an attractive force, they tend to stick at the poles when kept in a non-uniform magnetic field as their strongest at that point.

11. When ferromagnetic substances are placed in a watch glass on two pole pieces kept at a distance, the substance accumulates at the edges, leaving a depression in the middle as the field is strongest at the poles.

Concepts Related To Ferromagnetic Substances

Hysteresis Loop

Hysteresis is a property of substances that is also shown by ferromagnetic materials. When the applied external field is removed, a ferromagnetic substance doesn’t lose the induced magnetism. An external magnetic field is applied in the opposite direction to bring the generated magnetic field back to zero.

When a changing magnetic field is applied to a ferromagnetic substance and the magnetic flux of the material is measured simultaneously, the data is used to plot a graph known as a hysteresis loop.

To explain this further, consider a ferromagnetic rod placed inside a solenoid through which current is passed. At first, the current is increased, and the magnetic flux increases. After a specific time, saturation is achieved when no increase in flux can be seen with the increase in current. Now, the current is decreased back to zero, but the magnetization doesn’t follow the same curve. The decrease in flux lags, and a loop is formed. This is due to the property of retentivity and coercivity.

Curie Temperature

When the ferromagnetic materials are exposed to a temperature that is constantly increasing, there comes the point when the ferromagnetic material will start showing paramagnetic properties. This temperature point is called the Curie temperature, which means beyond this temperature, the material starts losing its magnetic property. Tc represents the Curie temperature. This is because the order of the dipoles in the domains is disrupted by thermal energy.

Curie temperature for some known elements are :

• Fe – 1043 K

• Ni – 627 K

• Gd – 293 K

• Co – 1388 K

Applications Of Ferromagnetic Material

Ferromagnetic materials are used in many industries like electrical, magnetic storage and equipment in electromechanics.

• Permanent Magnets, as the strength of the magnetism, is more in ferromagnets and they last longer.

• Transformer Core, as the material used to construct the transformer core is ferromagnetic because the core is exposed to abrupt cyclical changes.

• Magnetic Tapes and Memory Store as the magnetization of a substance depends on the cycle of the magnetic field exposure. That is why the magnetization value is the record of the exposed magnetic processes. This is how a ferromagnetic machine can be served as a memory storage unit.

Conclusion

The magnetic properties depend on its magnetic permeability and its magnetic dipole moment. The ferromagnetic substance produces attractive force due to the generation of a strong magnetic field when kept in an external magnetic field. These substances can be permanently magnetized after applying a magnetic field even once. This is due to the presence of domains that get aligned in the same direction as the applied magnetic field. These compounds also show the property of hysteresis, which means that they possess resistivity and coercivity. All ferromagnetic elements have a particular Curie temperature, which is a critical point above which the materials lose their ferromagnetic property. Some examples of ferromagnetic substances are cobalt, nickel, iron, etc.