1. When the temperature rises
• For most magnet materials, as the temperature increases, the surface magnetic flux density will gradually decrease. This is because the increase in temperature will intensify the thermal motion of the magnetic domains inside the magnet. Magnetic domains are small regions of spontaneous magnetization within magnetic materials, and their orderly arrangement forms the magnetism of the magnet. When the temperature rises, the energy of the thermal motion of the magnetic domains increases, which will disrupt the original orderly arrangement of the magnetic domains, making the microscopic magnetic structure inside the magnet disordered and thus weakening the magnetism of the magnet. Correspondingly, the surface magnetic flux density will decrease.
• For example, Nd-Fe-B magnets are a common type of high-performance magnets. However, their Curie temperature (the temperature at which the magnetism changes abruptly) is generally around 310 - 350 °C. When the temperature approaches or exceeds this range, their magnetism will rapidly weaken and the surface magnetic flux density will also drop significantly. In practical applications, if Nd-Fe-B magnets work in a high-temperature environment, such as the high-temperature environment generated when a motor operates under high load for a long time or in magnetic equipment close to a heat source, the surface magnetic flux density will decrease.
2. When the temperature drops
• When the temperature drops, generally speaking, the surface magnetic flux density of the magnet will increase. This is because the decrease in temperature weakens the thermal motion of the magnetic domains, making it easier for the magnetic domains to maintain their orderly arrangement and thus enhancing the magnetism of the magnet. However, this change is not absolute and is also related to factors such as the material characteristics of the magnet.
• For example, for some special magnetic materials, after undergoing specific temperature treatments, the magnetic domain structure inside them may undergo irreversible changes. Even if the temperature returns to its original state, the surface magnetic flux density may not return to its previous value.
3. Differences among different materials
• Different materials of magnets have different sensitivities to temperature. For example, SmCo magnets have a relatively high working temperature range and good temperature stability. Compared with Nd-Fe-B magnets, they can maintain the surface magnetic flux density better at higher temperatures. This is because the material structure of SmCo magnets makes the magnetic domains inside them more resistant to interference in a high-temperature environment. Therefore, in some precision instruments with high temperature requirements or high-temperature working environments, SmCo magnets have an advantage.
• While ferrite magnets have relatively weak magnetism, within a certain temperature range, the change in their surface magnetic flux density with temperature is relatively gentle. This is because the internal structure and magnetic domain characteristics of ferrite magnets determine that they have stronger tolerance to temperature changes. In some common application scenarios that are less sensitive to temperature changes, such as ordinary speakers and other equipment, ferrite magnets can play a stable role.
