Magnets can lose their effectiveness. There are mainly the following situations that may lead to the failure of magnets:
Influence of Temperature
• Every type of magnet has its Curie temperature. The Curie temperature refers to the temperature at which a material can change between being ferromagnetic and paramagnetic. When the ambient temperature exceeds the Curie temperature of a magnet, significant changes will occur to the magnetism of the magnet. For example, the Curie temperature of Nd - Fe - B magnets is around 300 - 400 °C. If Nd - Fe - B magnets are exposed to such a high-temperature environment, the arrangement of the magnetic domains inside them will be disrupted, resulting in a sharp decline or even a complete loss of magnetism, thus making the magnets ineffective.
• Even if the temperature does not reach the Curie temperature, relatively high or low temperatures may also have a certain impact on the magnetism of the magnets. In a low-temperature environment, the magnetic performance of the magnets may decline, while in a high-temperature environment, the intensified thermal motion will damage the orderliness of the magnetic domains, thereby weakening the magnetism.
External Magnetic Field Interference
• When a magnet is in a powerful external magnetic field, the arrangement of its internal magnetic domains may be changed. If the external magnetic field is strong enough and acts for a long time, the magnet may be remagnetized, resulting in a change in the direction of its original magnetic poles or a weakening of its magnetism. For example, near some large electromagnetic equipment, such as powerful electromagnets or around transformers, the magnetic field strength is very high, and ordinary magnets placed in these areas may be interfered with and become ineffective.
Mechanical Damage
• When magnets are subjected to severe impacts, vibrations, or excessive bending, stretching and other mechanical actions, the arrangement of the internal magnetic domains may be damaged. For magnets like Nd - Fe - B magnets that are hard but brittle in texture, after suffering a strong impact, the magnetic domains may be misaligned, thus weakening or even eliminating the magnetism. In addition, for some thin, sheet-shaped magnets, excessive bending may also lead to the failure of the magnetism.
Corrosion Effect
• Many magnets may undergo chemical reactions on their surfaces if they are exposed to a humid environment with corrosive gases (such as those containing sulfur dioxide, hydrogen chloride, etc.) for a long time. For example, ferrite magnets may rust, and if the coating on the surface of Nd - Fe - B magnets is damaged, the internal metal will also be corroded. Such corrosion will affect the microstructure of the magnets, which in turn will lead to a decline in magnetism and may eventually make the magnets ineffective.
