Diamagnetism

Diamagnetism is the property of materials that are repelled by a magnetic field. When an applied magnetic field creates an induced magnetic field in these materials in the opposite direction, it causes a repulsive force.

In this article, we will see What is Diamagnetism, Types of Magnetic Materials, Properties of Diamagnetic Materials, Examples of Diamagnetic Materials, Applications of Diamagnetic Materials, and others in detail.

What is Diamagnetism ?

Diamagnetism was first observed by S.J. Brugmans in 1778 and later studied by Michael Faraday, who named the phenomenon. Diamagnetism is the property of materials that causes them to be repelled by a magnetic field. When an external magnetic field is applied, it induces a magnetic field in the opposite direction of the material, resulting in a repulsive force. This phenomenon is observed in substances with a symmetric electronic structure and no permanent magnetic moment. These materials are called diamagnetic materials.

Before proceeding any further we must first learn about Types of Magnetic Materials

Types of Magnetic Materials

Magnetic materials can be classified into several categories based on their response to magnetic fields. The main types of magnetic materials are:

• Ferromagnetic Materials
• Paramagnetic Materials
• Diamagnetic Materials
• Antiferromagnetic Materials
• Ferrimagnetic Materials
• Superparamagnetic Materials

Classification of Magnetic Materials

Magnetic materials are mainly classified into three types which are explained in the table below,

Ferromagnetic Materials	Paramagnetic Materials	Diamagnetic Materials
These materials, such as iron, cobalt, and nickel, are strongly attracted to a magnetic field and can retain their magnetic properties, making them useful for applications like motors, generators, and transformers.	Paramagnetic materials, like aluminum, titanium, and platinum, are weakly attracted to a magnetic field and have a small magnetic moment. They are used in scientific research and medical imaging.	Diamagnetic materials, including zinc, mercury, lead, sulfur, copper, and bismuth, are repelled by a magnetic field. They have a slightly negative susceptibility and are magnetized when placed in a strong magnetic field. However, their magnetization is very small.

What are Diamagnetic Materials?

Diamagnetic materials are substances that, when placed in a magnetic field, become magnetized in the opposite direction to the applied magnetic field. It causes them to be repelled by the magnetic field. Diamagnetic materials have a weak, negative susceptibility to magnetic fields, meaning a magnetic field slightly repels them and does not retain magnetization.

In periodic table the substances that shows Diamagnetism are, Gold, Silver, Copper, etc.

Theory of Diamagnetism

Langevin Theory of diamagnetism, proposed by Paul Langevin, provides a classical-based model to explain the diamagnetic behavior of materials. The theory is an approximation based on classical physics and yields results that are in good agreement with experimental observations.

Key concept in the Langevin theory is the behavior of the electrons in the material when subjected to an external magnetic field. The theory assumes that the material has classically bound electrons, and it considers the response of these bound electrons to the applied magnetic field.

Derivation of Langevin’s susceptibility, which quantifies the material’s response to the magnetic field, is based on the assumption of a classically bound electron. The susceptibility is expressed as:

χ = e²Zr²μ₀/6mV

where,

• e is Charge of Electron
• Z is Number of Electrons Per Unit Volume
• r is Mean Radius of Electron’s Path
• μ_o is Permeability of Free Space
• m is Mass of Electron
• V is Volume over which Magnetic Field Acts

Expression for susceptibility provides insight into fundamental factors influencing the diamagnetic behavior of materials, particularly role of electron motion and material’s volume.

Properties of Diamagnetism

Properties of diamagnetism are:

• Diamagnetic materials have a slightly negative magnetic susceptibility and a lower relative permeability than unity.
• They have all paired electrons, and none of the electrons is valence, resulting in absence of atomic magnetic moments.
• Diamagnetic materials do not obey Curie’s Law.
• Diamagnetism is a fundamental property of all matter, although it is often overshadowed by other, stronger magnetic effects such as paramagnetism and ferromagnetism.
• Diamagnetic materials can be found in solids, liquids, and gases.
• Diamagnetic materials have a very low or minimal magnetic effect due to the absence of unpaired electrons.

Magnetic Susceptibility (of Magnetic Materials at 20°C)

Magnetic susceptibility measures how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization M (magnetic moment per unit volume) to the applied magnetizing field H. Magnetic susceptibility indicates whether a material is attracted into or repelled out of a magnetic field.

At 20°C, magnetic susceptibility of some materials are as follows:

Elements	Magnetic Susceptibility
Ammonia	-0.26
Bismuth	-16.6
Mercury	-2.9
Silver	-2.6
Carbon (Diamond)	-2.1

Examples of Diamagnetism

Example of Diamagnetism is as follows:

Frog in Magnetic Field

One example of diamagnetism is levitation of a frog in a magnetic field. When a frog is placed in a strong magnetic field, water in its body, which is diamagnetic, is repelled by the magnetic field, causing the frog to levitate. This phenomenon results from the diamagnetic repulsion between the magnetic field and the water in the frog’s body.

Levitation of the frog is a visual demonstration of diamagnetism and is a result of the weak, negative magnetic susceptibility of diamagnetic materials. Other examples of diamagnetic materials include water, graphite, and silver.

Applications of Diamagnetism

Diamagnetism has various applications, which are:

Magnetic Levitation

Diamagnetic materials can be levitated in a strong, inhomogeneous magnetic field, demonstrating the phenomenon of magnetic levitation. This property has been used in research and demonstration experiments, such as levitating small objects like graphite and live organisms like frogs.

Magnetic Shielding

Diamagnetic materials can be used for magnetic shielding, which involves creating a barrier that redirects magnetic fields away from sensitive equipment or devices. It protects sensitive electronic devices, scientific instruments, and medical equipment from external magnetic interference.

Superconductors

Superconductors exhibit perfect diamagnetism and are used in applications such as magnetic levitation trains (maglev), MRI machines, and energy-efficient power transmission. They expel external magnetic fields from their interior, a property known as the Meissner effect.

Meissner Effect

Meissner Effect is a phenomenon observed in superconductors, where these materials expel all magnetic fields from their interior when cooled below a critical temperature. This results in the magnetic field being bent around the superconductor. Meissner effect is a manifestation of perfect diamagnetism in superconductors, leading to the complete expulsion of magnetic fields from their interiors, a property that is not observed in normal materials.

This effect is a defining characteristic of superconductivity and results from the absence of electrical resistance in superconducting materials, allowing them to maintain persistent screening currents that oppose any applied magnetic field.

Diamagnetism Frequently Asked Questions

What are Diamagnetic Materials with Examples?

Diamagnetic materials create a weak magnetic field in opposition to an externally applied magnetic field. An example is bismuth.

Is Diamagnetism Strong?

Diamagnetism is generally weak compared to other types of magnetism, like paramagnetism and ferromagnetism.

What is Difference between Paramagnetic and Diamagnetic Materials?

Paramagnetic materials are weakly attracted to magnetic fields, while diamagnetic materials are weakly repelled. This difference arises from how their electrons behave in an external magnetic field.

Do Diamagnetic Materials Obey Curie’s Law?

Diamagnetic materials do not obey Curie’s law, which applies to paramagnetic and ferromagnetic materials.

Is Diamagnetism Present in All Materials?

Diamagnetism is present in all materials to some extent, but other types of magnetism usually overshadow it in most substances.

What is Diamagnetism and Ferromagnetism?

Ferromagnetic materials are strongly attracted to both poles of magnets. whereas Diamagnetic materials are unique materials they repel both poles of magnets.