Magnetism and Classification of Magnetic Materials
Magnets and magnetic fields produce a classic phenomenon that is known as Magnetism. Its origin is dependent on the orbital movements of the electrons of the element. It might be a surprising fact for you, but every matter has some magnetic property, and the only difference that is there is in respect to the amount of magnetism present. Moreover, the classification of the materials is done based on their magnetic properties.
Types of Magnetic Materials
Now, moving on to the classification of a magnet; it happens based on magnetism and goes as follows:
Diamagnetism
Paramagnetism
Ferromagnetism
Ferrimagnetism
Antiferromagnetism.
The matters showing Paramagnetism and Diamagnetism are the ones that do not exhibit any magnetic interactions. However, the ones in the other three groups show a long-range magnetic order after certain temperature conditions.
Ferromagnetic and Diamagnetic materials are opposite to each other. When the former one shows magnetic behaviour, the latter one does not exhibit any such property.
What is Diamagnetism?
Now, how should we define diamagnetic materials?
A diamagnetic material is one that has a very low or minimal magnetic effect due to the absence of any unpaired electrons in them.
Another way for explaining diamagnetic meaning is through Lenz’s law. It states that diamagnetic materials get induced dipoles in the presence of an external magnetic field, and this happens in such an order that the magnetic field and the induced dipoles repel each other.
What is Diamagnetic Material?
Moving on to the substances available globally, what are diamagnetic materials?
In 1845, Michael Faraday discovered diamagnets and the meaning of diamagnetic materials. Further, with the creation of the modern-day periodic table, experts commented and proved that most of the elements are Diamagnetic, like Gold, Silver, Copper, etc. These di-magnetic elements cover the majority of the table, and the other categories have a lesser number of elements. Moreover, semiconductors are the best diamagnetic materials. They also exhibit the diamagnetic field and this perfect diamagnetism in the superconductor is known as the Meissner effect.
Diamagnetic Properties
After understanding the diamagnetic definition well, let us move further with the properties. Properties of the diamagnetic materials are:
The diamagnetic materials have all the paired electrons, and none of the electrons is the valence, resulting in the absence of atomic dipoles in these materials. This happens because the overall magnetic moment of each atom in the compound cancels out.
In the presence of the magnetic field, there is a repulsion between the diamagnetic substance and the magnet.
The field weakly repels the substances having diamagnetism; thus in the non-uniform field’s presence, these substances move from the stronger region of the magnetic field to the weaker one.
In comparison to the magnetizing field, magnetization intensity is lower in the negative direction, and proportional.
Diamagnetic materials have lower and negative magnetic susceptibility.
The relative permeability is also a bit lower than unity.
The materials that exhibit diamagnetism do not obey Curie’s Law. They are independent of the action of temperature.
When suspending a rod of some material following diamagnetic definition in the uniform magnetic field, it comes to rest in the perpendicular direction with respect to the magnetic field. This happens as the magnetic field is highest at the poles.
A diamagnetism-exhibiting liquid placed in a U-shaped tube gets depressed in the limb that is in the middle of the magnetic poles.
The dipole moment of the di-magnetic substances is lower and in the opposite direction of the magnetic field H.
When placing a diamagnetic liquid in a watch glass and then keeping the glass between two poles that stays closely, liquid accumulates at the sides of the glass. The liquid exhibits depression in the middle as the magnetic field is the strongest there.
When placing a diamagnetic liquid in a watch glass and then keeping the glass between two poles that stay far apart, liquid accumulates in the middle of the glass. This reaction occurs because the magnetic field is weaker in the centre.
Fun Facts on Diamagnetic Substances:
Diamagnetic properties cause the objects to levitate. Unbelievable, right? But this is a proven fact!
The reason is that the diamagnetic materials get magnetism only in the presence of the magnetic field, and these induced fields are opposite to the acting magnet. This is why they get utilized in many experiments for levitating the objects.
Moreover, even the Maglev train works with the help of this property of diamagnetism. Additionally, once a frog also got levitated in the presence of a strong magnetic field in an experiment.
FAQs on Diamagnetism
1. What is diamagnetism, and can you provide some common examples?
Diamagnetism is a magnetic property of certain materials that causes them to be weakly repelled by an external magnetic field. This phenomenon occurs in substances where all electrons are paired, so there is no permanent net magnetic moment per atom. When placed in a magnetic field, a weak magnetic moment is induced in the direction opposite to the applied field. Common examples of diamagnetic materials include bismuth, copper, gold, silver, water, and nitrogen gas.
2. What are the key properties of diamagnetic materials as per the CBSE 2025-26 syllabus?
According to the CBSE Class 12 Physics syllabus for 2025-26, the primary properties of diamagnetic materials are:
- They are feebly repelled by magnets and tend to move from a stronger to a weaker part of the magnetic field.
- Their magnetic susceptibility (χ) is small and negative.
- Their relative magnetic permeability (μᵣ) is slightly less than one.
- They do not have permanent atomic magnetic moments because their electrons exist in pairs.
- The property of diamagnetism is independent of temperature.
3. Why are diamagnetic materials weakly repelled by a magnetic field?
The repulsion of diamagnetic materials is a direct consequence of Lenz's Law. When a diamagnetic substance is placed in an external magnetic field, the orbital motion of its paired electrons is altered. This change induces a small magnetic dipole moment within each atom that is directed opposite to the external field. The sum of these induced opposing moments creates a net magnetic field that repels the material from the source of the external field.
4. How does diamagnetism fundamentally differ from paramagnetism?
The fundamental difference lies in their atomic structure and response to a magnetic field:
- Origin: Diamagnetism arises from paired electrons, while paramagnetism is due to the presence of one or more unpaired electrons in the atoms.
- Interaction: Diamagnetic materials are weakly repelled from a magnetic field. Paramagnetic materials are weakly attracted to it.
- Magnetic Moment: Diamagnetic materials have no permanent atomic magnetic moments. Paramagnetic materials possess permanent magnetic moments that align with an external field.
- Susceptibility: The magnetic susceptibility is small and negative for diamagnetic materials, but small and positive for paramagnetic ones.
5. What is the significance of magnetic susceptibility (χ) and relative permeability (μᵣ) for diamagnetic substances?
For diamagnetic substances, these two values quantify their response to a magnetic field. A negative magnetic susceptibility (χ) signifies that the induced magnetism opposes the applied external field, causing repulsion. The relative permeability (μᵣ) being slightly less than 1 (μᵣ < 1) indicates that the magnetic field lines are less dense within the diamagnetic material compared to a vacuum, physically demonstrating this repulsive effect.
6. How does a change in temperature influence the magnetic behaviour of a diamagnetic material?
The magnetic behaviour of a diamagnetic material is almost entirely independent of temperature. This is because diamagnetism is caused by the induced magnetic moments from the orbital motion of electrons, which is a quantum mechanical effect not significantly influenced by the random thermal vibrations of the atoms. This makes it distinct from paramagnetism, whose susceptibility decreases with increasing temperature (Curie's Law).
7. What is the Meissner effect, and how does it demonstrate perfect diamagnetism?
The Meissner effect is the phenomenon where a material, upon transitioning into a superconducting state by being cooled below its critical temperature, expels all magnetic field lines from its interior. By completely excluding the magnetic field, it acts as a perfect diamagnet. For a perfect diamagnet, the magnetic susceptibility (χ) is -1, which is the strongest possible diamagnetic response, showcasing a perfect repulsion of the magnetic field.
8. Are everyday substances like water or even living organisms diamagnetic?
Yes, many common substances exhibit diamagnetism. Water (H₂O) is a well-known diamagnetic material. Consequently, living organisms, which are predominantly composed of water, including humans, are also inherently diamagnetic. This property, while very weak, is the reason behind scientific demonstrations where small animals like frogs can be levitated in extremely powerful magnetic fields.
