Diamagnetic Materials and Their Examples

Magnetism is an amazing force. You might sometimes wonder how such a phenomenon is possible. Every day, we come across objects such as water, wood, gold, etc., without even knowing that these materials show diamagnetism. These materials are diamagnetic materials that show the repelling property of the magnetic fields. 

A famous experiment was held in which a frog was levitated from a diamagnetic metal in the presence of other magnetic fields. Another experiment showed that water repels superconductors. It is terrific to see how these things can float and rise because of diamagnetism. Let’s look at what makes these materials diamagnetic and their applications.  

What are Diamagnetic Materials? 

Diamagnetic materials are materials and substances repelled by a magnetic field. That is because of the induced magnetic field created by the applied magnetic field in the opposite direction. An applied magnetic field induces a dipole in the material and the induced dipoles oppose the applied magnetic field. So, materials that have paired electrons are the property of diamagnetic materials. The material is known as diamagnetic, and this phenomenon is known as diamagnetism. Michael Faraday discovered diamagnetism in the 1840s, which Faraday’s Law can also prove.

We can see diamagnetic materials in our day-to-day life such as water, some plastics, wood, etc.  

Discovery of Diamagnetism

Brugmans first discovered diamagnetism in 1778. He first stated that magnetic fields repelled bismuth. It was finally in 1845 that Michael Faraday demonstrated that it was a property that was shown by matter when any magnetic field was applied.

Properties of Diamagnetic Materials

• The Diamagnetic materials set themselves perpendicular to the direction of the magnetic field when suspended freely in a uniform magnetic field. 

• They move from the stronger to the weaker part of the magnetic field when suspended freely in a non-uniform magnetic field.

• They have a relative permeability of less than 1.

• Their susceptibility is independent of temperature. 

• Magnets repel them. 

• The resultant magnetic moment is zero.

Importance of Diamagnetic Materials 

• These magnets are used as elements of most Magnetic Resonance Imaging (MRI) systems.

• Bismuth, which shows the strongest diamagnetism, is used in guns.

• Pyrolytic graphite is also a strongly diamagnetic material that can float in a magnetic field.

• These materials are temperature independent, so they do not melt in the heat.

Examples of Diamagnetic Materials

• Water

• Lead

• Carbon (diamond and graphite)

• Bismuth

• Silver

• Mercury

• Copper

• Neon

• Pyrolytic carbon

Diamagnetic Susceptibility

The average change in the magnetic moment per atom is called diamagnetic susceptibility. Magnetic Susceptibility is ꭓ < 0, which means it will always be a negative value. It is the ratio of magnetisation M to applied field H, χm = M/H.

General Points to Remember

• This effect is due to the induced field caused by the applied field, making the electrons move from stronger points to weaker points.

• If an electron rotates with an angular velocity (w), It will be producing a current (I) and magnetic field orthogonal to the plane. Then, the current will be given by

I = ew/2ꙥc

Where ‘e’ is the charge on an electron, and ‘c’ is the velocity of the light.

• The magnetic permeability of diamagnetic substances is less than the permeability of the vacuum.

• The relative permeability of diamagnetic materials is less than unity.

• The susceptibility can be defined as χv = μv – 1  

Application of Diamagnetic Materials or Diamagnetism

The usefulness of diamagnetism has led to many uses and applications of diamagnetic materials. Some of them are given below.

1. Powerful diamagnetic materials can be levitated if the magnets are strong enough.

2. The Meissner effect describes how certain materials and objects can be easily levitated in the presence of another powerful permanent magnet.

3. Superconductors are referred to as perfect diamagnetic materials.

4. Diamagnetic materials have the Bohr magneton of zero.

5. The material will not show diamagnetism if it has odd numbers of electrons.

Conclusion

Diamagnetic materials are those materials that people find non-magnetic such as wood, water, gold, copper, etc. These materials show the property of diamagnetism. They are not attracted to any magnetic field. This is because they have dipoles induced by the applied magnetic field, which thus creates an induced magnetic field. The induced magnetic field opposes the applied magnetic field, making the resultant magnetic moment zero.

Diamagnetism is present in all the materials, but this effect is so weak that it is neglected when compared with other paramagnetic and ferromagnetic effects.    

Diamagnetism is possible in solids, liquids, and gases. The role played by Brugmans remains unrecognised as he only said that A magnetic field repelled bismuth. Also, this phenomenon was named by Faraday. There are many applications of diamagnetic Materials. Some super magnets are also classified as diamagnetic objects.

If a super magnet is covered with a layer of water, the water slightly repels the magnet or vice versa. This experiment can easily show that the water is a diamagnetic material and it shows the properties of diamagnetism.

Also, in some cases, diamagnetic effects have proved to be stronger than parametric effects. For example, gold has a magnetic susceptibility of less than 0, but if it is measured carefully with X-Ray magnetic circular dichroism, it shows weak paramagnet effects. A stronger diamagnetic field or effect can overcome this effect.