Ferromagnetic substances are materials that can be magnetized and retain their magnetic properties even after an external magnetic field is removed. Common examples include iron, nickel, and cobalt. These materials have regions called magnetic domains, which align in the presence of a magnetic field, resulting in a net magnetic moment. The ability of ferromagnetic substances to become magnetized is due to the alignment of their atomic magnetic moments. When heated above a certain temperature, known as the Curie temperature, these materials lose their ferromagnetic properties as the thermal energy disrupts the alignment of the magnetic domains.