MadSci Network: Physics Query:

### Re: What can you use to cancel out Magnetism

Date: Thu May 3 18:02:15 2007
Posted By: Prater Brian D., Staff, Magnetics, Cavetronics R&D labs
Area of science: Physics
ID: 1178115689.Ph
Message:
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Hello, Kevin

Diamagnetism is a form of magnetism that is only exhibited by a substance
in the presence of an externally applied magnetic field. It is the result
of changes in the orbital motion of electrons. Applying a magnetic field
creates a magnetic force on a moving electron in the form of F = Qv × B.
This force changes the centripetal force on the electron, causing it to
either speed up or slow down in its orbital motion. This changed electron
speed modifies the magnetic moment of the orbital in a direction opposing
the external field.

Consider two electron orbitals; one rotating clockwise and the other
counterclockwise. An external magnetic field into the page will make the
centripetal force on an electron rotating clockwise increase, which
increases its moment out of the page. That field would make the
centripetal force on an electron rotating counterclockwise decrease,
decreasing its moment into the page. Both changes oppose the external
magnetic field into the page. However, the induced magnetic moment is very
small in most everyday materials.

Fritz London and Heinz London developed the theory that the exclusion of
magnetic flux is brought about by electrical "screening currents" that
flow at the surface of the superconducting metal and which generate a
magnetic field that exactly cancels the externally applied field inside
the superconductor. These screening currents are generated whenever a
superconducting metal is brought inside a magnetic field. This can be
understood by the fact that a superconductor has zero electrical
resistance, so that "eddy currents", induced by the motion of the metal
inside a magnetic field, will not decay. Fritz, at the Royal Society in
1935, stated that the thermodynamic state would be described by a single
wave function.

http://en.wikipedia.org/wiki/Diamagnetic
http://en.wikipedia.org/wiki/Bismuth http://en.wikipedia.org/wiki/Superdiamagnetism

Magnons  http://en.wikipedia.org/wiki/Magnon

Thanks
Brian D. Prater
Cavetronics Labs

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