Answer 4—Iron, nickel, and cobalt are ferromagnetic, as are some of the rare earths like gadolinium and dysprosium. Ferromagnetic materials exhibit a long-range ordering phenomenon at the atomic level, which causes the unpaired electron spins to line up parallel with each other. Ferromagnetism is demonstrated by the fact that a small externally imposed magnetic field, say, from an electrical solenoid, can cause the magnetic domains to line up with each other and increase the total field by a factor of up to several thousand.

Contributor: David Tweed

Published December 2003