n. The phenomenon whereby certain substances can become permanent magnets when subjected to a magnetic field.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. phenomenon exhibited by materials like iron (nickel or cobalt) that become magnetized in a magnetic field and retain their magnetism when the field is removed
Word Usage
"However, in ferromagnetism, which is many times stronger, they are aligned collectively, which makes the understanding of the physics much more difficult."