Diamagnetic Materials | Definition, Properties, and Applications, class 12

In this article, we will discuss what are diamagnetic materials? Definition, properties, and its application. So let’s get started…

What is diamagnetism?

Diamagnetism is the property of all the materials and, it always makes some weak contribution to the materials, when they are exposed to a magnetic field. However, there are some other forms of magnetism (such as ferromagnetism or paramagnetism) that are so much stronger than that of diamagnetism. When multiple different forms of magnetism are present in a material, the contribution of diamagnetic is generally negligible.

Classification of magnetic material with examples class 12
expulsion of magnetic fields within a diamagnetic material

All the diamagnetic materials are generally repelled by magnets. It happens because these materials produce an induced magnetic field in the opposite direction of an externally applied magnetic field. But on the other hand, the behavior of paramagnetic and ferromagnetic materials is exactly the reverse of this phenomenon.

Diamagnetism: It is the magnetism shown by the diamagnetic materials. When a diamagnetic material is placed in external magnetising field, it is feebly repelled by the magnetic field, and tends to move from stronger magnetic field to the weaker part of magnetic field.

What is diamagnetic materials?

Diamagnetic materials are those materials that can be freely magnetized when they are placed in the external magnetic field. But, the magnetization of these types of materials is in the opposite direction to that of the magnetic field. The magnetism that is described by these materials is known as diamagnetism.

Origin of diamagnetism class 12

Diamagnetic materials: Materials where the diamagnetic behaviour is in the strongest effect are termed diamagnetic materials, or diamagnets.

Some people generally think that diamagnetic materials are those materials that are non-magnetic, that include water, wood, and most organic compounds such as petroleum and some plastics, and many metals including copper, particularly the heavy ones with many core electrons, such as mercury, gold, and bismuth.

Pascal constant: The magnetic susceptibility values of various molecular fragments are called Pascal’s constants.

Magnetic permeability and susceptibility of diamagnetic materials

Diamagnetic materials, like water, or water-based materials, have a relative magnetic permeability that is less than or equal to 1, and therefore a magnetic susceptibility is less than or equal to 0 because the magnetic susceptibility is defined as χv = μv − 1. This means that diamagnetic materials are repelled by magnetic fields. However, diamagnetism is a very weak property, thus, its effects are not observable in our everyday life. For example, the magnetic susceptibility of diamagnets such as water is χv = −9.05×10−6.

The stronger diamagnetic material is Bismuth, have the magnetic susceptibility χv = −1.66×10−4, although pyrolytic carbon may have a susceptibility of χv = −4.00×10−4 in one plane. These values are orders of magnitude smaller than the magnetism shown by paramagnets and ferromagnets. Because χv is derived from the ratio of the internal magnetic field to the applied field. It is a dimensionless quantity.

Who discovered diamagnetism?

Diamagnetism was first discovered by Anton Brugmans when he observed in 1778 that bismuth was repelled by the applied magnetic fields. In 1845, Michael Faraday showed that it was a property of matter and concluded that every material responded to an applied magnetic field in either a diamagnetic or paramagnetic way. But on a suggestion by William Whewell, Faraday was the first who referred to the phenomenon as diamagnetic (the prefix dia- meaning through or across), and later, he changed it to diamagnetism.

What causes diamagnetism?

All the electrons in diamagnetic materials are paired, which means there are no unpaired electrons, due to this there is no permanent net magnetic moment per atom. Diamagnetic properties are caused by the realignment of electronic orbitals due to the impact of an external magnetic field. As a result, all the materials with paired electrons have diamagnetic properties.

When electrons revolve around the nucleus, magnetic fields are produced on the atoms of diamagnetic materials, which form small atomic current loops. When this material is placed in an external magnetic field, these current loops tend to align in such a way that it opposes the applied magnetic field.

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Properties of diamagnetic materials

Some important properties of diamagnetic materials are given below.

  • Diamagnetic materials do not have atomic dipoles because the magnetic moment of each atom is zero due to coupled electrons.
  • Diamagnetic materials are feebly repelled by the external magnetising field.
  • Because the field repels the substances only weakly, they tend to moves from a strong to a weak region of the external magnetic field in a non-uniform field.
  • The magnetization’s strength (I) is a tiny, negative number that is proportional to the magnetic field.
  • Magnetic susceptibility is negligible and tiny. The permeability ratio is somewhat less than one.
  • The temperature does not affect diamagnetic materials. Curie’s law does not apply to these materials.
  • When hanging in a homogeneous magnetic field, a rod of diamagnetic material comes to rest with its length perpendicular to the field direction because the field is highest at the poles.
  • In a U-Tube, a diamagnetic liquid depresses the Limb between the poles of a magnet.
  • The magnetic dipole moment is tiny and polarised in the opposite direction as the magnetic field H.
  • If a diamagnetic liquid is placed in a watch glass between two pole pieces that are very near to one other, liquid collects on the sides and depression appear in the centre, where the field is greatest.
If a watch - glass containing a small quantity of water is placed on two dissimilar magnetic poles, then water.
Depression of diamagnetic liquid at the center when poles are nearer (left), But the liquid collects at the center when poles are apart (right), source: toppr
  • When a liquid is poured on a watch glass that is placed over two pole pieces that are suitably spaced apart (more than in the previous example), liquid collects in the middle, where the field is weakest.
  • Diamagnetic properties arises from the realignment of electronic orbitals due to the impact of an external magnetic field.

Applications of diamagnetic materials or diamagnetism

Some applications of diamagnetism are given below:

  • Superconductors (where electrical resistance is zero and magnetic flux fields are expelled from the material) may be considered a perfect diamagnets (χv = −1), because they expel all magnetic fields (except in a thin surface layer) due to the Meissner effect. The Meissner effect describes how certain materials may be easily levitated in the presence of a powerful permanent magnet.
Diamagnetism & Diamagnetic Materials - Definition, Properties, and Applications
The transition from ordinary conductivity (right) to superconductivity (left). At the transition, the superconductor expels the magnetic field and then acts as a perfect diamagnet. source: Ques 10
  • If a powerful magnet (such as a supermagnet) is covered with a thin layer of water then the field of the magnet notably repels the water. This repulsion causes a slight dimple in the water’s surface that can be seen by a reflection in its surface.
  • As we know that the diamagnetism is the expulsion of magnetic fields within a material or vice-versa. If there is a powerful diamagnetic materials then it may be levitated, or levitate magnets if they are sufficiently strong and large enough. The diamagnetic levitation of pyrolytic graphite over permanent neodymium magnets can be seen in the diagram below.
Diamagnetism & Diamagnetic Materials - Definition, Properties, and Applications
pyrolytic carbon sheet is levitated by its repulsion from the strong magnetic field of neodymium magnets. source: Phys.org

Some diamagnetic materials, and its magnetic susceptibility

Materialsχm [× 10−5 (SI units)]
Bismuth−16.6
Carbon (diamond)−2.1
Carbon (graphite)−1.6
Copper−1.0
Lead−1.8
Mercury−2.9
Neon−6.74
Pyrolytic carbon−40.9
Silver−2.6
Superconductor−105
Water−0.91

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