Diamagnetism

Diamagnetism is a property of all materials, and always makes a weak contribution to the material's response to a magnetic field. However, other forms of magnetism (such as ferromagnetism or paramagnetism) are so much stronger that when multiple different forms of magnetism are present in a material, the diamagnetic contribution is usually negligible.

Overview

Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted by a magnetic field. Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic.

Diamagnetic materials

In diamagnetic materials, there are no unpaired electrons, so the intrinsic electron magnetic moments cannot produce any bulk effect. In these cases, the magnetization arises from the electrons' orbital motions, which can be understood classically as follows:

• When a material is put in a magnetic field, the electrons circling the nucleus will experience, in addition to their Coulomb attraction to the nucleus, a Lorentz force from the magnetic field.

• If the field is non-uniform, the electrons move from the high-field regions to the low-field ones.

• This is equivalent to a magnetic moment pointing in the opposite direction, which tends to align itself against the applied field.

Applications

Diamagnetism is used in various real-world applications. For example, it is used in magnetic levitation, where it can cause certain materials to levitate above a super-cooled magnet. This principle is used in maglev trains, which float above the tracks without touching them.

See also

• Magnetism
• Paramagnetism
• Ferromagnetism
• Superdiamagnetism

References

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Diamagnetism

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  Graphite levitating over magnets due to diamagnetism
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  Interaction of diamagnetic material in a magnetic field
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  Expulsion of magnetic field lines in a diamagnetic material
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  Frog levitating in a magnetic field due to diamagnetism