Horseshoe magnet. Cluster of iron filings being attracted by a horseshoe magnet. Iron is ferromagnetic. This means that when iron filings are bought close to a magnet the individual filings will become tiny magnets themselves. The filings will have a north seeking and a south seeking pole. The poles will attract to the poles of the horseshoe magnet causing the filings to cluster on the magnet. The behaviour induced in the filings by the horseshoe magnet will last to some degree after the horseshoe magnet is removed.