Demagneetisoituminen

Demagneetisoituminen, or demagnetization, is the process by which a formerly magnetized material loses its permanent magnetic properties. When an object such as a bar magnet, magnetic core, or permanent magnet is exposed to conditions that alter the alignment of its magnetic domains, the net magnetic field decreases or vanishes entirely. This phenomenon occurs naturally in geological contexts and can also be induced by human interventions.

The most common causes of demagneetisoituminen include temperature fluctuations, mechanical shock, and exposure to external magnetic fields that are opposite in direction or of higher intensity. Heating a magnet to a critical temperature, known as the Curie point, randomizes domain orientation. Similarly, subjecting a magnet to a strong alternating field or to vibration can redistribute domain walls, eventually reducing magnetization. In metallurgical processes, welding or rapid cooling can also lead to significant loss of magnetism.

Different materials exhibit varying resistance to demagneetisoituminen. Ferrites and neodymium‑iron‑boron alloys retain magnetism well at moderate temperatures but deteriorate when exposed to higher heat or excessive magnetic perturbations. The extent to which a magnet can be remagnetized after losing its field depends on the material’s coercivity—the ability to resist demagnetizing influences.

Measurement of remnant magnetization is typically performed with vibrating sample magnetometers or inductive coils that detect the magnetic flux density. Engineers use these measurements to assess the longevity and reliability of magnetic components in motors, transformers, and data storage devices. In safety applications, accurate knowledge of residual magnetism helps prevent unintended magnetic interactions in environments containing elevators, surgical instruments, or aircraft navigation systems.