Types of Ferromagnetic Materials

The French physicist Louis Eugene Felix Neel invented ferromagnetic materials or substances. He also brought forward the point that the atoms present in those materials are examples of ferromagnetic materials and can arrange themselves in domains, which is the name given to small groups of ferromagnetic materials. Every domain has a different magnetic dipole moment. 

Ferromagnetic Substances and Types of Ferromagnetic Materials

• Ferromagnetic substances are the substances in which there is a non-zero magnetic moment in each atom, molecule or ion as in paramagnetic substances. When such substances are placed in an external magnetising field, they get strongly magnetised in the direction of the field and are strongly attracted to magnets.

• Examples: Cobalt, Iron, Nickel, Neodymium magnet, Chromium dioxide, Gadolinium, Terbium, Dysprosium.

Ferromagnetic Materials

1. Unmagnetised or ferromagnetic materials

• Soft type of materials

• Hard type of materials

• Ferrites

2. The Magnetised and the Non-ferromagnetic materials

• Ferromagnetic materials permanently get magnetised in the direction of the applied magnetic field. The atoms/molecules of ferromagnetic material have permanent magnetic dipole moments and these molecules behave as small magnetic dipoles. 

• The magnetic dipole moment is very powerful for every atom. When these molecules/atoms interact with other atoms/molecules around them, they try to arrange other atoms/molecules’ magnetic dipole moment in the same direction as theirs. Due to this, it forms small groups of atoms/molecules in ferromagnetic materials, called domains. 

• Each domain is a strong magnet without any external magnetic field, but still, these ferromagnetic materials do not act as a magnet.

• In the absence of an external magnetic field, the magnetic moments of different domains are randomly oriented, because of which the resultant magnetic dipole moment or magnetisation of these materials is zero. 

M = O ,Unmagnetised

• However,  if we apply an external magnetic field on these materials, the domain starts to rotate till their magnetic moments are aligned in the direction of the applied magnetic field and arranged to form a single giant domain.

M ≠0 ,Magnetised

• That is why ferromagnetic materials attract or get magnetised strongly towards external magnetic fields.

• Now, if we heat a magnetised ferromagnetic material, then the domain structure of that material gets distributed and because of that, the magnetic dipole moment of the domain gets randomly arranged in different directions and gets magnetised. Therefore, the ferromagnetic materials’ net magnetic dipole moment or magnetisation decreases as temperature increases.

                  ↑ Magnetised α 1/Temperature↓

Properties of Ferromagnetic Materials

• They often get magnetised in an external field’s direction, where they have been placed.

• They have a strong tendency to move from a region of a magnetic field to a region of strong magnetic field. Hence, they get strongly attracted to a magnet.

• In any magnetised material, the total magnetic field B and external magnetic field, B0 ratio is called relative magnetic permeability (μ r). As ferromagnetic materials always attract or get magnetised in the direction of the applied magnetic field, the total magnetic field B is larger as compared to the external magnetic field B0. That is why the relative magnetic permeability (μ r) value of these ferromagnetic materials is considered to be much larger than 1.

μr = B/B0

B>>B0

So, μr>>1

• The susceptibility of ferromagnetic materials is very large which is why they can be magnetised easily and strongly ( ∼103 to 105).

Xm= μr – 1

Xm=large positive value

• With the rising temperature, the susceptibility of ferromagnetic materials decreases. At a certain temperature, the ferromagnetic changes over paramagnetic. This transition temperature is called curie’s temperature.

• The magnetic field lines pass through the piece instead of passing through the air when a ferromagnetic substance is placed in a magnetic field.

B = B0 + Bm

B>>B0

• If we hang any ferromagnetic material in a uniform magnetic field, then that metal with its longest axis aligns itself in the external magnetic field.

Conclusion

In this article, we have covered ferromagnetic substances and how many types of Ferromagnetic materials are there. We have learned that Ferromagnetic substances are those in which each atom has a non-zero magnetic moment as in paramagnetic substances. When such substances are placed in an external magnetising field, they are strongly magnetised in the direction of the field. That’s why they are strongly attracted to magnets. The types of ferromagnetic materials are unmagnetised or ferromagnetic material and magnetised or non-ferromagnetic material. In ferromagnetic substances, atoms form a very large number of small effective reasons called domains.