HOW LONG IS THE LIFE OF A NEODYMIUM MAGNET?
A neodymium magnet is called a permanent magnet, can it be used forever? Here, we will introduce how the magnet should be used, in what environment, and how it should be used to prolong its life.
■ Neodymium magnets are called permanent magnets, how long is its life?
A permanent magnet is a magnet in which the direction of the magnetic pole is fixed and the magnetic force is generated. One of them, the neodymium magnet, is known to have a particularly strong magnetic force.
Not only neodymium magnets but all permanent magnets also have a decrease in magnetic force. This phenomenon is called demagnetization.
The demagnetization of neodymium magnets is less than that of other magnets, and is about 0.1 to 0.3% per year. Even after 100 years, demagnetization is unlikely to occur due to the performance of the magnet. So it is not an exaggeration to say that they can be used semi-permanently. The life of a magnet is much longer than the life of the equipment and machinery that uses it. Therefore, it is used for personal computers, mobile phones, motors, headphones, etc.
Depending on the environment and usage, the life span can be shortened significantly. The speed of magnetic force loss of a magnet tends to be faster when used in high temperature conditions or in environments that are susceptible to shock. Such use makes demagnetization easy, so the life span of the neodymium magnet will be shortened.
■ The main reason for shortening the life span of a neodymium magnet
The magnet retains its magnetic force because the magnetic molecules inside are facing the same direction. However, due to some reasons, the order of the magnetic molecules can be disturbed and change direction. Then the magnetic force will weaken. Here are the four main reasons.
1. Self-demagnetization
The magnetic force usually leaves the N pole, passes through the external environment and goes to the S pole. However, the magnetic field lines inside the magnet will bypass the magnet without going to the external environment, so the magnetic field created is in the opposite direction to the magnetic field of the magnet. This magnetic field is called the demagnetization field and it reduces the magnetic force.
The magnitude of the demagnetization field varies depending on the size and shape of the magnet, but the thinner the magnet, the stronger the self-demagnetization ability, so it is said that the magnetic force tends to weaken.
2. Influence of external magnetic fields
External magnetic fields are magnetic fields that act on the magnet from the outside. For example, if there are machines or components with large electromagnetic forces nearby, demagnetization can occur under the influence of the magnetic field. Because, when an external magnetic field is opposite to the magnetization direction of the magnet, the magnetic flux density changes and the magnetic force weakens. This phenomenon can especially occur with ferrite magnets with small coercivity. Therefore, in environments with devices that generate magnetic fields in the vicinity, it is better to choose magnet materials other than ferrite magnets, such as neodymium magnets.
3. Demagnetization due to high temperature
Neodymium magnets are relatively weak magnets to heat. Basically, ferromagnetic metals change their properties such as magnetic flux density and coercivity by thermal energy when the temperature increases. The temperature at which the magnet loses its magnetic force in this way is called the Curie temperature.
Curie temperature, or Curie point (often denoted as Tc, is a concept in solid state physics, materials science is the phase transition temperature in ferromagnetic or ferroelectric materials, named after the French physicist Pierre Curie (1859 – 1906). The Curie temperature in ferromagnetic materials is the temperature of the ferromagnetic – paramagnetic phase transition. Below the Curie temperature, the material is ferromagnetic, above it, the material will lose its ferromagnetic properties and become paramagnetic. For rare earth magnets (white magnets), the Tc temperature is 320 degrees Celsius.
The Curie temperature depends on the type of magnet. Ferrite magnets are about 500 ° C, samarium cobalt magnets are about 700-800 ° C, but the Curie temperature of neodymium magnets is as low as about 320 ° C. Therefore, neodymium magnets are not suitable for high temperature applications. In addition, the magnet has been replaced structure changes when exceeding the Curie temperature, so the magnetic force will not be restored when cooled again.
4. Demagnetization due to low temperature
Ferrite magnets cause demagnetization not only at high temperatures but also at low temperatures. Because ferrite is different from other magnets, it has the characteristic that the coercivity decreases with decreasing temperature. Therefore, if the ferrite magnet is cooled at a low temperature of -20 to -40 ° C, it will not return to its original magnetic force when it returns to normal temperature.
■ How to extend the life of neodymium magnets
Here we will introduce ways to extend the life of rare earth magnets.
1. Storage with non-magnetic materials
Choose a non-magnetic material such as a wooden box to store the magnet.
2. Storage in a dry place
Rare earth metals react very strongly with oxygen, so rare earth magnets are very susceptible to rust. When rust will weaken the magnetic force, so it must be stored in a dry place. For rare earth magnets, before leaving the factory, the product is often plated with a protective layer: nickel, zinc, gold, epoxy, phosphate
3. Avoid high temperatures and special environments
Rare earth magnets are more sensitive to heat than other magnets, so use or store them in environments below 50 ° C if possible. Also, avoid special environments that use corrosive gases, strong acids, strong alkalis, and organic solvents.
Rare earth magnets are more sensitive to heat than other magnets, so use or store them in environments below 50 ° C if possible. Also, avoid special environments that use corrosive gases, strong acids, strong alkalis, and organic solvents.
