Diamagnetism Definition and Examples

There are different forms of magnetism, a list that includes ferromagnetism, antiferromagnetism, paramagnetism, and diamagnetism.

Diamagnetism

In chemistry and physics, to be diamagnetic indicates that a substance contains no unpaired electrons and is not attracted to a magnetic field. Diamagnetism is a quantum mechanical effect that is found in all materials, but for a substance to be termed "diamagnetic" it must be the only contribution to the matter's magnetic effect.

A diamagnetic material has a permeability less than that of a vacuum. If the substance is placed in a magnetic field, the direction of its induced magnetism will be opposite to that of iron (a ferromagnetic material), producing a repulsive force. In contrast, ferromagnetic and paramagnetic materials are attracted to magnetic fields.

Sebald Justinus Brugmans first observed diamagnetism in 1778, noting antimony and bismuth were repelled by magnets. Michael Faraday coined the terms diamagnetic and diamagnetism to describe the property of repulsion in a magnetic field.

Examples

Diamagnetism is seen in water, wood, most organic molecules, copper, gold, bismuth, and superconductors. Most living organisms are essentially diamagnetic. NH₃ is diamagnetic because all the electrons in NH₃ are paired.

Usually, diamagnetism is so weak it can only be detected by special instruments. However, diamagnetism is strong enough in superconductors to be readily apparent. The effect is used to make materials appear to levitate.

Another demonstration of diamagnetism may be seen using water and a super magnet (such as a rare earth magnet). If a powerful magnet is covered with a layer of water that is thinner than the diameter of the magnet, the magnetic field repels the water. The minor dimple formed in the water may be viewed by reflection in the water's surface.

Sources

• Jackson, Roland. "John Tyndall and the Early History of Diamagnetism." Annals of Science.
• Kittel, Charles. ","Introduction to Solid State Physics 6th edition. John Wiley & Sons.
• Landau, L.D. "Diamagnetismus der Metalle." Zeitschrift für Physik A Hadrons and Nuclei.