A drum-like rotor having numerous, closely spaced, elongated rows forms of permanent magnets arranged end-to-end and secured to the outer surface of the rotor, produces a high-density, rapidly reversing magnetic field in a band-like zone which is spaced a short distance from,and extends along the length of,the rotor outer surface. The magnetic field induces eddy currents in pieces of different metals passed through the zone which produces repulsive magnetic forces of different intensities in different metal pieces, and thus, magnetically separates such pieces. The rows of magnets, in their radial direction, are alternatingly thicker and thinner,so that the outer surface of the thinner rows are depressed relative to their adjacent thicker rows. The outer surface of the magnets of each thicker row have a polarity which is opposite to the polarity of their next adjacent thicker row magnets, and the direction of the magnetic polarity of the magnets of the thicker rows are radial relative to the rotor. The side edges of the magnets of the thinner rows have the same polarity as the polarity of the outer surfaces of their adjacent thicker row magnets. The directions of the magnetic polarity of the thinner row magnets are generally circumferential, relative to the rotor. Thus, magnetic flux flows transversely through each of the thinner row magnets and then radially outwardly through their adjacent thicker row magnets, returning over the exposed surfaces of the thinner row magnets to the next adjacent row of thicker magnets and, therefore, radially inwardly of the rotor and transversely of the thinner row. Thus, the direction of the magnetic flux flow through the zone changes as the successive thicker and thinner rows pass alongside of the zone as the rotor rotates.