Diamagnetism

Magnetic properties of a substance are its response to an external magnetic force. Depending on magnetic properties of solids, they can be classified into three types :

  • Diamagnetic
  • Paramagnetic
  • Ferromagnetic

What is Diamagnetism?

Diamagnetic materials usually repel from a magnet. Technically, these solids create an induced magnetic field in a direction opposite to an externally applied magnetic force and are repelled by the applied magnetic field. This phenomenon is just the opposite behaviour exhibited by paramagnetic materials.

The orbital motion of electrons present on the atoms of diamagnetic solids produces magnetic fields as it creates tiny atomic current loops. When an external magnetic force is applied to a material, these current loops tend to align in such a way as to oppose the applied field.

In diamagnetic materials, there is no permanent net magnetic moment per atom as all the electron are paired. Due to the influence of an external magnetic force, diamagnetic properties arise from the realignment of the electron paths. Most elements in the periodic table like copper, silver, and gold, are diamagnetic in nature. Sebald Justinus Brugmans discovered diamagnets in the year 1778. Michael Faraday further demonstrated that diamagnetism or magnetism is a property of a matter and every material or solid reacts accordingly.

Magnetic Susceptibilities of Diamagnetic Materials at 20°C

Km is the relative permeability which is nothing but a quantity which measures the ratio of the internal magnetization to the applied magnetic field.

Material χm=Km-1

(x 10-5)

Carbon (graphite) -1.6
Ammonia -.26
Silver -2.6
Bismuth -16.6
Carbon (diamond) -2.1
Mercury -2.9
Lead -1.8
Water -0.91
Copper -1.0
Sodium chloride -1.4

The gases N2 and H2 are weakly diamagnetic with susceptibilities -0.0005 x 10-5 for N2 and -0.00021 x 10-5 for H2. The gases N2 and H2 are weakly diamagnetic with susceptibilities -0.0005 x 10-5 for N2 and -0.00021 x 10-5 for H2.

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Practise This Question

A lens of power + 2 diopters is placed in contact with a lens of power – 1 diopter. The combination will behave like