Should the poles at the end of each magnet be similar?

[arety33]

Hi, I have a question about magnetism.
If 2 magnets are used to pick up iron shavings, and the magnet are connect with paramagnetic material and turned into a U-shape.
Should the poles at the end of each magnet by similar or dissimilar to pick up the iron shavings most effectively?

 

[Meir Achuz]

They should be of opposite polarity so that the B field in the iron goes from one magnet to the other. If they wer of the same polarity, B in the iron would tend to cancel. Try it experimentally.

 

[arety33]

I think the domains the the iron field at the beginning is random oriented, but if one polarity is used to pick up the iron shavings, the domains will all point to the same direction. But if the other magnet is different polarity, the domains will begin to point in the other direction and cancel out the other domains. Then the iron shavings will not be picked up.