Diamagnetism

Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. It is the result of changes in the orbital motion of electrons due to the external magnetic field. The induced magnetic moment is very small and in a direction opposite to that of the applied field. When placed between the poles of a strong electromagnet, diamagnetic materials are attracted towards regions where the magnetic field is weak. Diamagnetism is found in all materials; however, because it is so weak it can only be observed in materials that do not exhibit other forms of magnetism. Also, diamagnetism is found in elements with paired electrons. Oxygen was once thought to be diamagnetic, but a new revised molecular orbital (MO) model confirmed oxygen's paramagnetic nature.

Diamagnetic levitation

Diamagnets can be used for levitation. The materials required for this set up are two diamagnets, one small rare-earth magnet, and one larger rare earth magnet.

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Begin by placing one of the diamagnets on a flat surface. Set the small rare earth magnet on top and in center of it. On the edges of the diamagnet, place spacers that will hold up the second diamagnet (pennies or something similar will work fine), and place the second diamagnet on top of the spacers.

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At this point, there should be the two diamagnets stacked on top of one another with enough room for the small magnet to float up and down between them. While not necessary, it can be helpful to tape the entire assembly down to the surface it is sitting on.

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To levitate the small magnet, slowly bring the larger magnet down from above. At some point, the small magnet will lift off of the bottom diamagnet and float in mid air. If the larger magnet gets closer, the small magnet will fly up; if the larger magnet moves farther away, the small magnet will drop.

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It is easiest to understand why this set up is stable if it is examined in individual pieces. To begin with, there are two main forces acting on the small magnet: gravity and magnetism. Gravity from the Earth is pulling down on the magnet, and the bottom diamagnet is pushing up on the magnet. The force of gravity is far greater, so the magnet stays down.

Related Topics:
Gravity - Magnetism

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As the large magnet is lowered down toward the small magnet, a point is reached where its magnetic field is pulling up on the small magnet with a force that is equal to the force of gravity (which is pulling down). At this point, the magnet is effectively weightless, and the only remaining force acting upon it is from the diamagnets.

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Once the force of gravity is effectively negated by the large magnet, the small magnet can now respond to the small force from the bottom diamagnet. This force moves the small magnet up until the force from the bottom and top diamagnets equals one another. At this point, the magnet is stably levitated.

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In summation, the large magnet negates the force of gravity on the small magnet, and the diamagnets create a magnetic field where the small magnet can stably rest between them.

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