Is there such a material that can prevent two permanent
attracting each other within a distance of 10mm?
The simplest way would be to arrange them north pole to north pole, then
they would repel each other rather than attract each other.
A more elaborate solution which will greatly reduce (but not eliminate) the
attraction would be to place a magnetic shielding structure between them.
These are typically made of multiple layers (spaced with a non-magnetic
material such as aluminum) of a material with a very high affinity for
magnetic fields, such as mu-metal. The magnetic fields are 'trapped' in
the layers of the mu-metal and do not extend much beyond it.
The catch 22 is that the magnets are strongly attracted to the shield so
they both still have a strong force pulling them toward the shield, even
though they are not interacting with the other magnet.
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Update: June 2012