Paramagnetism

File:Liquid oxygen in a magnet 2.jpg

Liquid oxygen (blue) can be suspended between the poles of a strong magnet as a result of its paramagnetism.

Paramagnetism is a form of magnetism whereby certain materials are attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field. Ferromagnetic materials like iron and nickel do not exhibit paramagnetism.

History

The concept of paramagnetism was first introduced by Michael Faraday in 1845. Faraday discovered that some atoms could be induced to produce a magnetic field, but the effect was weak and disappeared when the inducing field was removed.

Theory

Paramagnetism occurs due to the presence of unpaired electrons in the atomic orbitals of an atom. These unpaired electrons are free to align their individual magnetic moments with the external field, which results in a net magnetic moment in the direction of the applied field.

Examples

Examples of paramagnetic materials include oxygen and aluminum. These materials are only magnetic when in the presence of an external magnetic field.

See also

• Diamagnetism
• Ferromagnetism
• Superparamagnetism