Diamagnetic Materials

Bookmark added to your notes.
View Notes
×

What are the Diamagnetic Materials?

Diamagnetic materials repel the magnetic field like an external magnetic field and generate an induced magnetic field in the materials in the opposite direction, creating a repulsive force. In contrast, the ferromagnetic and paramagnetic materials are attracted by a magnetic field. Diamagnetism, which is a quantum mechanical effect, happens in all materials. If it is the only contribution to magnetism, the material is referred to as diamagnetic.

In ferromagnetic and paramagnetic substances, the weak diamagnetic force is overcome with the attractive force of magnetic dipoles in the material. The magnetic permeability of the diamagnetic materials is less than the permeability of the vacuum, μ0. Diamagnetism is a weak effect in many of the materials, that can be detected only by the sensitive laboratory instruments; a superconductor, besides, acts as a strong diamagnet due to the reason, it repels a magnetic field completely from its interior.

Properties of Diamagnetic Materials

A few and important properties of Diamagnetic Materials are listed below.

  • Diamagnetic materials are always repelled by a magnet.

  • The substances are repelled weakly by the field, and so in a nonuniform field, they tend to travel from a strong to a weak part of the external magnetic field.

  • There are zero atomic dipoles in diamagnetic materials due to the resultant magnetic moment of each atom is zero because of the paired electrons.

  • The intensity of magnetization is negative, very small, and proportional to the magnetizing field.

[image to be added Soon]

  • The relative permeability is slightly less to that of unity.

  • Magnetic susceptibility is negative and small.

  • These materials are independent of temperature and they do not obey Curie’s law.

  • A rod with a diamagnetic material comes to rest with its length perpendicular to the field direction when it is suspended in a uniform magnetic field because the field is strongest at the poles.

[image to be added Soon]

  • A diamagnetic liquid present in a U-Tube depresses in the Limb between the poles of a magnet.

[image to be added Soon]

  • The moment of the magnetic dipole is opposite to the magnetic field H and it is small.

  • If a diamagnetic liquid is kept in a watch glass (placed on two pole pieces which are closer to each other), then the liquid accumulates at the sides and shows depression in the middle, the point where the field is strongest.

[image to be added Soon]

  • If a liquid is kept on a watch glass placed over two pole pieces which are sufficiently apart (more than the preceding case), then, the liquid accumulates in the middle in the weakest field.

[image to be added Soon]

  • The diamagnetism origin is the induced dipole moment due to the change in the motion of the orbital of electrons in atoms by the applied field

Superconductors

Superconductors are strong diamagnetic materials, exhibit a volume susceptibility of χv = − 1 (dimensionless). They obey the perfect diamagnetic screening and can be considered as the perfect diamagnets because they tend to expel all magnetic fields.

Diamagnetic Materials examples and Demonstration

A few of the most common diamagnetic materials examples are Zinc, Copper, Silver, Bismuth, Gold, Marble, Antimony, Water, NaCl, Glass, and more.


The Diamagnetic Material Units can be Tabulated as Below:

Material

χv [× 10−5 (SI units)]

Superconductor

-105

Bismuth

-16.6

Pyrolytic Carbon

-40.9

Silver

-2.6

Mercury

-2.9

Lead

-1.8

Carbon (Diamond)

-2.1

Carbon (Graphite)

-1.6

Water

-0.91

Copper

-1.0

Meissner Effect

If a permanent magnet is induced near a superconductor, the superconducting material causes a current which opposes the magnetic field completely applied using a permanent magnet. 

By the superconductor, an applied magnetic field is expelled, and due to this, the field is zero in its interior. Thus a superconductor in a Meissner state behaves like a perfect diamagnet.

Applications of Diamagnetic Materials or Diamagnetism

As diamagnetism is importantly an expelling of magnetic fields within a material, the strong diamagnetic materials can be levitated, or if they are sufficiently strong and sufficient area, can levitate magnets. The below diagram shows the diamagnetic levitation of pyrolytic graphite over the permanent neodymium magnets.

[image to be added Soon]

In the superconductors case, which is given in the below diagram, the diamagnetic response leaves zero internal magnetic fields. These materials can be levitated easily in the presence of a strong permanent magnet, as seen in the above figure, and this is called the Meissner effect. 

However, superconductors with high temperatures (~100 K) are made from exotic materials with expensive processing routes and need cryogenic fluids to accomplish the superconducting state.

In the below diagram, the superconductor (blue colour) expels all of its external magnetic fields, which are called perfect diamagnets.

[image to be added Soon]

Frog in the Magnetic Field

In a 15-Tesla magnetic field, a frog is levitated. In the frog’s body, the levitation force is exerted on the diamagnetic water molecules. This is the best-known example of diamagnetism.

[image to be added Soon]

Key Points To Remember

A few of the key points to remember are listed below.

  • Diamagnetism exists in all materials and is independent of temperature, but the effect is so weak. Thus it is often neglected in comparison to the ferromagnetic and paramagnetism effects.

  • Diamagnetism is possible in the three states as, solids, liquids, and gases.

FAQ (Frequently Asked Questions)

1. Is Water Diamagnetic in Nature? Why?

Ans: It is stated that water is diamagnetic. Diamagnetic molecules contain only the electron pairs. However, water contains two bonding pairs of electrons between the hydrogen and oxygen atoms and two lone pairs of electrons which are present in the oxygen atom.

Paramagnetic molecules at least have one unpaired electron. This occurs when the molecule has an odd number of electrons (like in NO). It also occurs when there are even numbers of electrons (as in O2) in a few molecules.

We can notice that the water repels the magnet. This occurs because whenever we get any magnetic field near water, it creates its own magnetic field and thus repels the magnet, which is called diamagnetism.

2. How to Identify if a Molecule is Either Paramagnetic or Diamagnetic?

Ans: We can determine whether a material is either diamagnetic or paramagnetic by using a Gouy balance method. If we place material near a strong magnet, the paramagnetic materials are attracted to the magnet of the balance, where the diamagnetic materials are repelled.

It is also pointed out that all paramagnetic materials are also diamagnetic, but diamagnetic materials are not required to be paramagnetic. 

The force the Gouy balance method exerts on a paramagnetic material has both a paramagnetic component and a diamagnetic component. However, typically, the diamagnetic component is much weaker than that of the paramagnetic component.