Permanent magnets are materials that can be magnetized and remain magnetized indefinitely, but they can also lose their magnetism over time or under certain conditions. This process is called demagnetization.
What Is Magnet Demagnetization?
Magnetic demagnetization is the process of reducing or eliminating the magnetic properties of a material. It is commonly used to remove the residual magnetization that may remain in a ferromagnetic material after it has been magnetized and then de-energized, or to remove the magnetization from a material that has been intentionally magnetized.
What Factors Will Cause Demagnetization?
If you want to prevent your magnet from becoming demagnetized, you should avoid exposing it to factors such as high temperatures, impact, age, electrical current, corrosion, exposure to other magnets, and exposure to electromagnetic fields. It’s important to handle and store magnets carefully to preserve their magnetic properties.
However, if you want to demagnetize a magnet, there are several methods you can use.
1. Heat Demagnetization
Heat demagnetization occurs when the temperature of a permanent magnet exceeds a certain level, known as the Curie temperature or Curie point.
At this temperature, the magnetic domains within the magnet become disordered and the magnetic field becomes weakened or disappears entirely. The Curie temperature varies depending on the material of the permanent magnet. For example, the Curie temperature of “N” Grade neodymium magnets, which are commonly used in many applications, is around 310°C.
The below table shows the Curie temperature of different grade series of NdFeB magnets:
| Grade Series | Maximum Working Temperature（℃/℉） | Curie Temperature（℃/℉） |
| “N” Series | 80℃/176℉ | 310℃/590℉ |
| “M” Series | 100℃/212℉ | 340℃/644℉ |
| “H” Series | 120℃/248℉ | 340℃/644℉ |
| “SH” Series | 150℃/302℉ | 340℃/644℉ |
| “UH” Series | 180℃/356℉ | 350℃/662℉ |
| “EH” Series | 200℃/392℉ | 350℃/662℉ |
It’s important to note that heat demagnetization is reversible, and the magnet can regain its original magnetic field strength once it has cooled down to a lower temperature. However, if the magnet is heated above the Curie temperature for an extended period, it may become permanently demagnetized.
There are several tools that can be used for heat demagnetization:
- Ovens: Ovens are commonly used to apply heat to a material for heat demagnetization. The material is placed in the oven and heated to a certain temperature for a certain amount of time, depending on the specific material and desired level of demagnetization.
- Induction heaters: Induction heaters use an electromagnetic field to heat a material through induction. These heaters are often used for heat demagnetization because they can heat material evenly and quickly.
- Resistance heaters: Resistance heaters use electricity to generate heat by passing an electric current through a resistive element, such as a coil of wire. These heaters are often used for heat demagnetization because they can be easily controlled and can heat material quickly and evenly.
2. Electrical Demagnetization:
Electrical demagnetization is a process in which the magnetic field of a magnet is reduced or eliminated by exposing it to a strong electrical current.
This process is often used to prepare magnets for recycling or to remove any residual magnetism that may be present in materials that need to be demagnetized for scientific or technical purposes.
The electrical demagnetization process typically involves passing a high-voltage, low-amperage current through the magnet or material being demagnetized. The current creates a strong electromagnetic field that temporarily aligns the magnetic domains within the magnet in the opposite direction, effectively neutralizing the magnet’s magnetic field.
There are several tools that can be used for electrical demagnetization:
- AC demagnetizers: AC demagnetizers use an alternating current (AC) to reduce the magnetization of a material. The AC current is applied to the material using a coil of wire, and the frequency and intensity of the current can be adjusted to achieve the desired level of demagnetization.
- DC demagnetizers: DC demagnetizers use a direct current (DC) to reduce the magnetization of a material. The DC current is applied to the material using a coil of wire, and the intensity of the current can be adjusted to achieve the desired level of demagnetization.
- Pulsed DC demagnetizers: Pulsed DC demagnetizers use a series of short pulses of DC current to reduce the magnetization of a material. The pulses of current are applied to the material using a coil of wire, and the intensity and duration of the pulses can be adjusted to achieve the desired level of demagnetization.
It’s important to note that electrical demagnetization is not always effective, and the magnet may not be completely demagnetized. In some cases, it may be necessary to repeat the process several times or to use a different demagnetization method to achieve the desired level of demagnetization.
3. Mechanical Demagnetization:
Mechanical demagnetization is a process used to reduce the strength of a permanent magnet. It involves applying a mechanical force to the magnet in a specific way to disrupt the alignment of its magnetic domains, which are regions within the magnet where the magnetic moments of the atoms are aligned.
There are several methods of mechanical demagnetization, including hammering, bending, and torsion. These methods work by mechanically stressing the magnet, causing the magnetic domains within the magnet to become misaligned and reducing the overall magnetic field.
It’s important to note that mechanical demagnetization is not always effective, and the magnet may not be completely demagnetized. In some cases, it may be necessary to repeat the process several times or to use a different demagnetization method to achieve the desired level of demagnetization.
Additionally, mechanical demagnetization can cause physical damage to the magnet, so it’s important to use caution when using this method.
4. Magnetic Field Demagnetization:
The magnetic field demagnetization process typically involves exposing the magnet or material being demagnetized to a strong external magnetic field in the opposite direction to the magnet’s magnetic field. This causes the magnetic domains within the magnet to become misaligned, effectively neutralizing the magnet’s magnetic field.
There are several tools that can be used for magnetic field demagnetization, including:
- Electromagnets: Electromagnets are devices that use electricity to generate a magnetic field. They can be used to demagnetize a material by exposing it to a strong alternating magnetic field.
- Oscillating solenoids: Oscillating solenoids are devices that use electricity to generate a magnetic field that oscillates, or alternates, at a high frequency. They can be used to demagnetize a material by exposing it to a strong alternating magnetic field.
- Pulse magnetizers: Pulse magnetizers are devices that use high-voltage, short-duration pulses of electrical current to generate a strong magnetic field. They can be used to demagnetize a material by exposing it to a strong alternating magnetic field.
Can I Re-magnetize A Magnet After it is Demagnetized?
Yes, it is generally possible to re-magnetize a magnet after it has been demagnetized, although the magnet’s magnetism may not be fully restored to its original level.
Is Demagnetization Reversible?
Demagnetization is generally not reversible, meaning that it is not possible to fully restore the magnetism of a magnet after it has been demagnetized.
Regardless of the method used to demagnetize a magnet, the internal structure of the magnet will undergo permanent changes. As a result, it is not possible to fully restore the magnet’s magnetism after it has been demagnetized, even if it is re-magnetized.
The magnet’s magnetism may be partially restored, but it will not be able to achieve the same level of magnetism that it had before it was demagnetized. This is because the demagnetization process causes the magnetic domains within the magnet to become disordered and misaligned, and these changes cannot be fully reversed.
Demagnetization And Demagnetization Curve
A demagnetization curve is a graphical representation of the relationship between the magnetic field strength and the magnetization of a magnet. It is used to understand the behavior of a magnet under different field strengths and to predict its performance under various conditions.
Demagnetization is the process of reducing or eliminating the magnetic field of a magnet. The degree of demagnetization is typically measured in terms of the reduction in the magnet’s magnetic field strength or magnetization.
The demagnetization curve can be used to understand the behavior of a magnet during the demagnetization process. For example, by plotting the magnetic field strength and magnetization of a magnet on the demagnetization curve, it is possible to determine the point at which the magnet begins to become demagnetized and to predict how much the magnet’s magnetism will be reduced under different field strengths.
Conclusion
Thank you for reading our post on the demagnetization of a permanent magnet. We hope that you have a better understanding of this important process and how it can affect the performance of your permanent magnets.
At JDA Magnet Company, we are committed to providing our customers with the highest quality magnets and the knowledge they need to properly use and maintain them.
If you have any further questions or concerns about demagnetization or any other aspect of magnets, please don’t hesitate to contact us. We are here to help you get the most out of your magnets.
