By demagnetization is meant that the magnetism of the magnet is reduced or completely disappeared, and the permanent magnet operates based on the arrangement of micro-regions within the alloy material, these small regions are called domains, and each domain is like a micro-magnet in a larger whole. Part of the process of developing permanent magnets involves placing a high-strength magnetic material-usually alnico, strontium iron (known as ceramic or ferrite), neodymium iron boron, or samarium cobalt-in a strong magnetic field. In the process of magnetizing a material, individual magnetic domains, which generally point in all directions, will align with the direction of the magnetic field. When almost all the magnetic domains are aligned with the original magnetic field, the material becomes a permanent magnet. When you demagnetize a magnet, its domains are no longer perfectly aligned. It is the alignment of these domains that provides the magnetic properties of the material. When the magnetic field (magnetic domain alignment) is broken, the magnet has been demagnetized.

How is the permanent magnet demagnetized?

How does something called a permanent magnet demagnetize? People sometimes get confused about the terms "permanent" magnet and "temporary" magnet. Temporary magnets work like magnets only when attached or close to an object that emits a magnetic field. When the magnetic field source is removed, they quickly lose their magnetism. In contrast, permanent magnets generally maintain their permanent magnetic field independently under normal operating conditions. However, permanently magnetized materials can still undergo demagnetization under certain conditions, including exposure to high temperatures, collisions with other objects, volume loss, and exposure to conflicting magnetic fields. There are several factors that can cause permanent magnets to lose part or all of their magnetic field, and when this happens, it can adversely affect your application.

Heat

One of the most common causes of demagnetization is an increase in temperature. Increased heat means increased atomic motion, which eventually overwhelms the alignment of the magnetic domains. The Curie temperature is the temperature at which the magnetic alloy completely and irreversibly loses its permanent magnetism. However, as the temperature of the magnet approaches its Curie point, the demagnetization also changes to varying degrees. The level of demagnetization varies greatly depending on the material and grade of a particular magnet, and is described by the demagnetization curve of that magnet.

In general, some permanent magnet materials are more susceptible to demagnetization with increasing temperature than others, with neodymium magnets generally being most susceptible to elevated operating temperatures and generally resisting demagnetization until the operating temperature reaches about 100°C. Neodymium magnetic materials that can operate above 220°C can be used, but these materials can become very expensive. For samarium cobalt magnets, this limit is 350°C. Alnico magnets offer the best temperature characteristics of any available standard production magnet material and can be used in continuous service applications where extreme temperatures up to 540°C are expected.

When working at high temperatures, it is very important to know the permeability of the specific size magnetic material you are using. Size, material and operating temperature all play an important role in determining the overall effectiveness of the magnet for a given work purpose. For neodymium magnets, use the permeability coefficient calculator to help determine whether a magnet of a specific size will demagnetize and eventually lose its effectiveness at the operating temperature required for your application. When a permanent magnet is exposed to an elevated temperature for a long time, the electrons will be forced out of alignment and the magnet will be partially or completely demagnetized. The resulting demagnetization may be reversible or irreversible.

Collision and volume loss

Another factor that can demagnetize a permanent magnet is collision-the effect of another object on the magnet. For example, repeatedly hitting the magnet with a hammer will interfere with its atomic movement, affect the arrangement of the north and south poles of the magnet, and demagnetize it. Collisions can also affect the physical integrity of the magnet, and the resulting loss of volume can also adversely affect magnetization. This is why volume loss is considered to be another factor in the demagnetization of permanent magnets. Erosion or oxidation caused by over-wetting can also affect the physical properties, thereby affecting the magnetic properties of the magnet.

Conflicting Magnetic Fields

Exposure to an unfavorable external magnetic field can demagnetize the permanent magnet. When there is another magnetic field around the magnet, it will act as a demagnetizing force, and the magnet may be damaged. This is part of the reason why proper storage of permanent magnets is so important; it keeps your magnets magnetic by ensuring that your magnets are not only protected from collisions but also aligned in terms of magnetic field. Running an alternating current in the vicinity will also have this effect on the magnet, causing demagnetization.