We have read about magnetic susceptibility of a material earlier and we know this property is used for the classification of materials into diamagnetic, paramagnetic and ferromagnetic substances. We know that the material is diamagnetic if the value of χ is small and negative, paramagnetic if the value of χ is small and positive and ferromagnetic if the value is large and positive. In this section, we will learn more about these substances and how they are classified on the basis of their susceptibility.
Diamagnetic substances are those which have a tendency to move from stronger part of the external magnetic field to the weaker part of the external magnetic field. We can also say that the diamagnetic substances get repelled by a magnet.
Consider the figure shown above. We have a diamagnetic substance placed in an external magnetic field. We see that the field lined get repelled by the material and the field inside the material is reduced. If we place this substance in a non-uniform magnetic field, it tends to move from the point of high electric field to that of low electric field.
Paramagnetic substances are those substances that get weakly magnetized in the presence of an external magnetic field. In the presence of an external magnetic field, these substances tend to move from a region of a weak magnetic field to a region of strong magnetic field. In other terms we can say that these substances tend to get weakly attracted to a permanent magnet. In a paramagnetic material, the individual atoms possess a dipole moment, which when placed in a magnetic field, interact with one another, and get spontaneously aligned in a common direction, which results in its magnetization. As per the Curie’s law, the magnetism of a paramagnetic substance is inversely proportional to the absolute temperature, until it reaches a state of saturation.
Ferromagnetic substances are those substances that when placed in an external magnetic field, get strongly magnetized. Also, they tend to move from a region of weak magnetic field to the region of strong magnetic field and get strongly attracted towards a magnet. In a ferromagnetic material, the individual atoms possess a dipole moment, similar to a paramagnetic material. When placed in a magnetic field, the atoms interact with one another, and get spontaneously aligned in a common direction. The direction is common over a macroscopic volume which we term as a domain. The domain has a net magnetization and each domain directs itself in the direction of B0, which results in its strong magnetization.
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