By Timothy Boyer
Updated March 24, 2022
While the term “permanent” suggests enduring magnetic strength, certain conditions can erase that permanence. A strong external magnetic field or elevated temperature can disrupt a magnet’s ability to attract ferrous metals such as nickel, iron, and steel, effectively demagnetizing it.
The magnetic pull originates at the atomic level. Electrons orbiting an atom spin, generating a tiny magnetic dipole—essentially a miniature bar magnet with north and south poles. In a solid magnet, these dipoles cluster into domains, each acting like a magnetic brick. When domains align, the magnet’s field is strong; random alignment yields a weak field. Applying a powerful external field forces domains from order to disorder, thereby weakening or destroying the magnet.
Strong magnetic fields—whether from powerful permanent magnets or electric generators—can overpower weaker magnets. When a weak magnet’s field is oriented perpendicular to a stronger one, the stronger field can realign the weak magnet’s domains, turning a once strong magnet into a weakened or demagnetized piece.
Heat similarly agitates the atomic lattice. As temperature rises, atoms vibrate more vigorously. Beyond a critical threshold, these vibrations randomize domain alignment, converting an ordered magnetic structure into a disordered state. This threshold is known as the Curie point or Curie temperature.
Each magnetic metal has its own Curie point due to its unique atomic structure: iron – 1,418 °F, nickel – 676 °F, and cobalt – 2,050 °F. Below these temperatures, dipoles realign into an ordered, parallel configuration. If a heated magnet cools while aligned with a strong external field, it has a higher chance of regaining its original or even stronger magnetic strength.
