MadSci Network: Engineering

Re: Is there any material that can block a magnetic field?

Date: Mon Feb 2 22:30:56 1998
Posted By: Dewey Burbank, Senior Engineer, Chemical Engineering, SGN Eurisys Services Corp.
Area of science: Engineering
ID: 884633656.Eg

The strength of a magnetic field such as those generated by electromagnets 
or permanent magnets is measured by a property called magnetic 
susceptibility.  Permanent magnets are made of ferromagnetic materials, 
with typical magnetic susceptibilities of 10^3 to 10^5.

Most materials are paramagnetic, that is, their internal magnetic fields 
will tend to line up with an applied external field, increasing the 
overall field strength.  The magnetic susceptibility of paramagnetic 
materials is small, usually on the order of 10^-5 to 10^-3.

"Anti-magnetic" materials do exist, the terminology for these materials is 
diamagnetic.  When an external field is applied to a diamagnetic material, 
its internal fields will line up against the external field, thus 
decreasing the overall field strength.  However, their susceptibility is 
also small (and negative), ranging from -10^-5 to -10^-4.

So, although the answer to your question is technically YES, the magnetic 
susceptibility of these materials is millions of times smaller than a 
typical magnet, so the effect is negligible.  There are no known "anti-
ferromagnetic" materials.

For more information on this topic, check the web pages under the 
following link:

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