demagnetisere

Demagnetization, or demagnetising, is the process of reducing or removing a material's magnetic field. It occurs when the magnetic domains within a ferromagnetic material are randomized so that their net magnetization approaches zero. Demagnetization is used to prevent interference from stray magnetic fields, to erase data on magnetic media, and to prepare equipment for accurate operation.

Common methods include degaussing, which applies an alternating magnetic field with gradually decreasing intensity until the residual magnetization is eliminated; thermal demagnetization, which heats the material above its Curie temperature (or magnetic ordering temperature) and then cools it in zero field; and pulse demagnetization, which uses a sequence of decreasing magnetic field pulses. Some processes combine methods depending on the material and goal.

Applications include erasing data on magnetic tapes and older hard disks, degaussing cathode ray tube displays or other equipment to remove magnetic distortions, demagnetizing tools and parts to avoid attracting ferrous particles, and preparing instruments for precise magnetic measurements or calibration. Materials differ in response: soft magnets demagnetize easily; hard magnets and many permanent magnets retain magnetization and may require stronger or combined methods to reduce it.

Safety and practical considerations include the strong, changing magnetic fields involved, which can affect electronic devices, credit cards, and medical implants; use appropriate equipment and keep sensitive devices away. Some materials may incur irreversible changes if overheated or subjected to excessive fields.