What blocks a magnet's pull?

[OrionVTOL]

Many of you have done this in your past. Two magnets, one under a table, another on top of the table, and moving the one under will cause the one on top to move.

Is there a material that, given the same thickness, will block this magnetic pull/repelling between the two magnets?

Thanks.

[mgb_phys]

Yes, any high permeability metal will block magnetic fields.
The best is called mu-metal (http://en.wikipedia.org/wiki/Mumetal)

[pallidin]

Perhaps a more appropriate term instead of "blocking" is "re-direction"

[OrionVTOL]

So, this mu metal isn't something that magnets will attach to then. It talks about hard drives. Which part of a hard drive is this mu metal?

[mgb_phys]

Magnets don't attach to anything that isn't magnetic (ie not iron, cobalt, nickel)
What mu-metal (and other high P materials) do is to trap and guide magnetic field lines.

It is probably used to shield the arm stepper motor from the disk surface and read head.

[cjameshuff]

So, this mu metal isn't something that magnets will attach to then. It talks about hard drives. Which part of a hard drive is this mu metal?

They'll attach to it quite nicely, but (assuming the mu metal is thick enough for the magnet) little of the field will emerge from the far side, it will mostly remain inside the mu metal.

Superconductors might be more what you're thinking of. They actually do the opposite, excluding magnetic fields from their interior and repelling magnets:

http://en.wikipedia.org/wiki/Meissner_effect

[OrionVTOL]

What I would like to find is a material [material A] that a magnet [magnet A] would not be attracted to and a magnet [magnet B], on the other side of a certain thickness [no more than a cm] of this material A, would not attract or repell magnet A.

[minomax]

What I would like to find is a material [material A] that a magnet [magnet A] would not be attracted to and a magnet [magnet B], on the other side of a certain thickness [no more than a cm] of this material A, would not attract or repell magnet A.

The FAA has strict rules for the shipping of magnets on commercial carriers. Companies all know the have to package them with alternating polarity to cancel out the fields. pallidin is correct, there is really no material that "blocks" the fields, only redirects them.

People have been searching for such a material in their desire to produce a 'motor' using only magnets without introducing an outside energy source.