How to prevent magnets from demagnetizing?
In daily life, you may have encountered this situation: a newly purchased floor fan starts up much slower than when it was first bought, after a year or two of use. This is due to the demagnetization of the magnets after prolonged use. Similar problems are also common in industrial equipment and power tools. It is worth noting that the magnetism of a magnet is not constant and is easily disturbed by external factors, causing the originally ordered magnetic domains to become disordered and the magnetic moments to cancel each other out. This leads to a decrease in magnetic force, reduced stability, or even complete failure.
Basic Knowledge of Magnetic Properties
1. Remanence Br
If we compare a magnet to a sponge, remanence is like the sponge fully soaked with water, representing the maximum magnetic force the magnet can exhibit. It refers to the magnetic induction intensity displayed by the magnet after being magnetized to technical saturation in a closed circuit and then having the external magnetic field removed.
2. Coercivity Hcb and Intrinsic Coercivity Hcj
Once the sponge is fully soaked with water, squeezing out the water until none remains, the force used for this is equivalent to coercivity. It is the value of the reverse magnetic field intensity required to reduce the magnetic induction intensity to zero during reverse magnetization of the magnet. At this point, the magnetization intensity of the magnet is not zero. it’s just that the applied reverse magnetic field and the magnet’s magnetization intensity are opposite in direction and cancel each other out. If the external magnetic field is removed at this stage, the magnet still retains some magnetic properties. Intrinsic coercivity, on the other hand, is the reverse magnetic field intensity required to reduce the magnet’s magnetization intensity to zero.
3. Maximum Energy Product (BH)max
The amount of water a sponge can completely absorb can be understood as its maximum energy product. This represents the magnetic energy density formed in the space between the poles of a magnet, the DC magnetic energy per unit volume of the air gap. Its magnitude directly reflects the performance level of the magnet.
Factors Affecting the Magnetic Properties of Magnets
If you notice any abnormal magnetism in the magnet during use, please immediately pay attention to the following environmental interference factors. We recommend that you discuss the specific application scenario in detail with your magnet supplier. They will provide a customized protection solution based on a professional assessment, effectively extending the magnet’s lifespan.
1. Temperature
As the ambient operating temperature continues to rise, thermal motion causes random rearrangement of the magnetic domains within the magnet, resulting in a decrease in remanence and magnetic energy product. When the temperature rises further to the Curie temperature, the demagnetization process becomes completely irreversible.
Protection Suggestions: We can select the corresponding grade based on the actual temperature of the magnet’s application scenario, thereby maximizing the avoidance of rapid demagnetization during use.
| Grade | Max Operating Temp (°C) | Curie Temp (°C) |
|---|---|---|
| N | 80 | 310 |
| M | 100 | 340 |
| H | 120 | 340 |
| SH | 150 | 340 |
| UH | 180 | 350 |
| EH | 200 | 350 |
| AH | 230 | 350 |
2. Mechanical Stress
Neodymium magnets are brittle and hard, similar to ceramics. Long-term exposure to vibrations, impacts, or bending environments can cause mechanical stress to destroy the internal crystal structure, leading to magnetic domain wall displacement or fracture, and permanent reduction in local magnetic field strength.
Protection Suggestions: If your project frequently operates in environments with vibrations, such as those from industrial motors, we recommend prioritizing the use of ferrite and AlNiCo magnets, which offer higher vibration resistance. In addition, you can choose an epoxy coating to increase surface thickness and improve toughness.
3. Magnetic Field Interference
Magnets are easily affected by external magnetic fields. When an external magnetic field, especially a reverse one, exists, it interferes with the magnetic domain arrangement. If the reverse magnetic field strength exceeds the magnet’s coercivity, it will trigger irreversible demagnetization. Even after removing the interference source, the energy product is difficult to restore to its original value. This is common in devices assembled with multiple magnets.
Protection Suggestions: If your project is frequently in complex magnetic fields, we recommend selecting NdFeB or SmCo materials with strong demagnetization resistance while maintaining magnetic performance. If the engineering design allows, we also recommend incorporating a steel shell structure into the design to minimize the impact of the magnetic field on the magnet.
4. Environmental Corrosion
The rare earth elements in neodymium magnets are highly chemically reactive, readily reacting with oxygen, moisture, or acids and alkalis to form non-magnetic oxides. These corrosion products coat the material surface, forming an insulating layer that obstructs magnetic flux paths, ultimately causing the magnet to demagnetize.
Protection Suggestions: If your project frequently operates in harsh environments, we recommend adding anti-corrosion coatings to the magnet surface to reduce the possibility of chemical substances corroding the interior. Below are common coating options.
| Coating Options | Application | Corrosion Resistance Level |
|---|---|---|
| Ni-Cu-Ni | Motors, sensors | Medium |
| Epoxy | Fans, automotive parts | High |
| Zinc | Tools, DIY projects | Low-Medium |
| Teflon/PTFE | Industrial equipment | Excellent |
| Rubber/Plastic | Water pumps, vibration motors | Medium |
| Gold/Silver | Sensors, medical equipment | High |
| Chrome | Tool casings | Medium |
5. Radiation and High-Energy Particles
High-energy radiation bombards magnet atoms, creating lattice defects, disrupting the orderly arrangement of magnetic domains, and reducing remanence and coercivity. This effect is commonly seen in aerospace or medical equipment and is usually irreversible.
Protection Recommendations: If your project frequently operates in high-energy radiation environments, we recommend prioritizing SmCo magnets as your first choice. They are commonly used in aerospace projects, have low temperature dependence, and can be supplemented with aluminum polymer for compliant shielding.
Contact Magnet Experts Immediately
There are many reasons affecting the magnetic properties of magnets. I believe this issue troubles many engineers. If you’re currently troubled by magnetic performance issues, please contact our expert team right away. TOPMAG has rich experience in this area and can provide free advice to help you advance your project.
FAQ Summary
What are the main causes of magnet demagnetization? Common causes include high temperature, mechanical impact, reverse magnetic fields, corrosion, and radiation.
What magnets to choose for high-temperature environments? It depends on the operating temperature: below 200°C, consider using NdFeB magnets. above 200°C, choose SmCo magnets.
How to avoid external magnetic field interference? Select materials with high Hcj, and also recommend removing external magnets.
What coatings can effectively prevent magnet corrosion? It depends on the actual application environment. different coatings are selected to address different environments.
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