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Diamagnetic materials create an opposing magnetic field when exposed to a strong one due to a change in electron orbit. Many non-magnetic materials possess diamagnetism, and the strongest diamagnetic materials are graphite and bismuth. Diamagnetic levitation can occur, and the best diamagnets are superconductors. Theories related to diamagnetic materials include the Bohr-Leeuwen theorem and Earnshaw’s theorem. Diamagnetism was first observed in the late 1700s and is used in powerful superconductors. NASA has studied the concept extensively for microgravity experiments.
Diamagnetic refers to the ability of a material to create an opposing magnetic field when exposed to a strong one. The effect is created by a change in the orbit of the electrons, which generate small currents to counteract magnetism from external sources. Many non-magnetic materials possess the qualities of diamagnetism, such as water, wood, plants, animals and humans. Millions of times weaker than a normal magnetic force, diamagnetism can cause levitation under the right circumstances.
Graphite and bismuth are the strongest diamagnetic materials. Organic compounds, such as petroleum and heavy metals, such as gold and mercury, are also strong. Such materials are repelled by external magnetic forces due to the eddy currents that form in their magnetic field. The best diamagnets are superconductors, which resist a magnetic field as they transform into a superconducting state, as explained by the Meissner effect.
One of the phenomena associated with this weak magnetic force is diamagnetic levitation. Stable equilibrium in a given magnetic field results in objects floating in free space, when the overall magnetic field strength is at its lowest. Molecules in living things, including water and proteins, are diamagnetic and only have gravity as the resisting force when diamagnetism is present. Small animals, such as frogs, can be levitated in this way, as demonstrated by experiments in small tubes.
Theories related to diamagnetic materials include the Bohr-Leeuwen theorem, which states that a system cannot depend on a magnetic field if it is at a stable temperature. Diamagnetism is more persistent at high temperatures. Earnshaw’s theorem explains the phenomenon by saying that a magnetic field focused one way need not be focused in another direction. It only applies to stationary magnets, while diamagnets can repel fields and levitate in free space.
Diamagnetism was first observed in the late 1700s, but the term was first derived in the mid-1800s by Michael Faraday, who discovered that all materials exhibit diamagnetic properties when exposed to a magnetic field. Today’s powerful superconductors make use of opposing magnetic forces. Small samples of water can be levitated and magnetic objects have been suspended for hours in vacuum environments without adding energy. The concept has also been studied extensively by the National Aeronautics and Space Administration (NASA) and should aid microgravity experiments on human bone and muscle, as well as the development of magnets that counteract Earth’s gravity.
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