Question

What are diamagnetic substances?

Answer 1

Hint: Diamagnetism is an inherent property of all materials and it always makes a weak contribution to a material’s response towards an externally applied magnetic field. Diamagnetic materials repel the magnetic lines of force, unlike the paramagnetic and ferromagnetic materials. Hence, all the materials, for which diamagnetism is the major magnetic property, are called diamagnetic substances, also known as diamagnets.

Complete step by step solution:
Let’s start by understanding the Diamagnetism phenomenon.
Diamagnetism is a quantum mechanical effect exhibited in all the materials, and when this is the only contribution towards the magnetic property of a material, the material is known as a diamagnetic material or diamagnets. The magnetic permeability $(\mu )$ of the diamagnets is less than the magnetic permeability in vacuum $({{\mu }_{0}})$. That is $\mu <{{\mu }_{0}}$, hence correspondingly the magnetic susceptibility $\chi $ is less than zero, since $\chi =\mu -1$. Generally, for most of the materials, the inherent diamagnetism is such a weak effect that its detection is only possible through sensitive equipment.
An example of diamagnet, which is used in real life is a superconductor in its superconducting state. In its superconducting state, the superconductor expels all the magnetic lines of force outside its body. This causes the diamagnet to levitate over a magnetic field due to the repulsion caused by the diamagnet towards the magnetic field. This technology is used in maglev trains to levitate the maglev over the tracks. Having no physical contact with the track drastically reduces the frictional force, hence the maglev train reaches higher speeds and uses lesser amounts of energy too.
Now, let’s understand the magnetic property in all the materials. Diamagnetism is always present in all the materials, and hence, makes a weak contribution to the material’s response to a magnetic field. However, the other magnetic forms such as paramagnetism and ferromagnetism are much stronger than that of diamagnetism. Therefore, for most of the magnetic materials, the contribution due to paramagnetic and ferromagnetic properties overpowers the contribution due to the diamagnetism property. Similarly, for materials not exhibiting any magnetic properties, even upon the application of external magnetic fields are usually the diamagnets. Examples of diamagnets include water, wood, petroleum compounds, plastics, gold, bismuth and mercury etc.

Note: Most of the natural diamagnetic materials which we find in real life at normal or room temperatures, their paramagnetic or ferromagnetic contribution would lower than the diamagnetic contribution of the material. However, the magnetic susceptibility value of these materials is very low. The magnetic susceptibility of most diamagnets is in the range of $({{10}^{-6}})$, such as that of water is $\chi =-9.05\times {{10}^{-6}}$. The most strongest diamagnetic material at room temperature is that of bismuth with $\chi =-1.66\times {{10}^{-4}}$.
However, all the materials upon becoming superconductors become perfect diamagnets. That is, their magnetic susceptibility value in the superconducting phase of the superconductors becomes -1, that is $\chi =-1$.