Curie Temperature of Neodymium Magnets
Like every other magnet, the Relationship between neodymium magnets and temperature is such that high temperatures make neodymium magnets weaker while cold temperatures make them stronger.
Regarding neodymium magnets and temperature, two terms are essential: operating and curie temperatures.
Operating Temperature and Curie Temperature
Operating temperature and Curie temperature are terms used to describe the two levels of heat exposure that matter in the lifetime of a neodymium magnet.
If you work with or are planning to work with neodymium magnets, you need to know what these terms mean to get the best from them.
What temperature do neodymium magnets lose their magnetism?
There is no doubt that the answer is when the actual working temperature of the neodymium magnet exceeds the operating temperature.
Operating Temperature
The operating or working temperature describes the temperature range a neodymium magnet can function correctly. The figure you should care about here is the max operating temperature or MaxOpTemp.
The max operating temperature describes the limit to which your neodymium magnet can get hot before it begins to suffer irreversible loss of magnetic force. The MaxOpTemp does not refer to the heat generated by the heat generator but the neodymium magnet’s heat.
So, given enough time, it is possible to heat a neodymium magnet to its MaxOpTemp even when the available heat is within the operating temperature limit.
Introduction to the Neodymium Temperature Range
There are several grades of neodymium magnets, each indicating a magnet’s ability to withstand heat. Every neodymium magnet grade starts with an N, followed by a figure and a conditional letter.
Below are the different neodymium magnet grades and what they mean.
| Grade | Meaning |
|---|---|
| N | Neodymium Magnets under this grade only have the preceding N and the following figure, e.g., N35, N38, N52. Such neodymium magnets possess a MaxOpTemp of 80°C or 176°F. |
| M | Neodymium magnets under this grade carry the letter M after their grade number. They have a max operating temperature of 100°C or 212°F. |
| H | Neodymium Magnets with the letter H will have a MaxOpTemp of 120°C or 248°F. |
| SH | Starting with the SH, neodymium magnets that carry two letters after their grade number belong to the high-temp neodymium magnets class. This grade can take up to 150°C or 302°F. |
| UH | Neodymium Magnets with the letters UH after their grade number have a max operating temperature of 180°C or 356°F. |
| EH | Neodymium magnets with EH after the grade will have a MaxOpTemp of 200°C or 392°F. |
| TH/AH | Neodymium magnets that have TH or AH after the grade number, i.e., N52AH, will have a MaxOpTemp of 220°C to 230°C or 428°F to 446°F. |
Curie Temperature
The Curie Temperature indicates how hot a piece of neodymium magnet can get before it permanently loses its magnetic force. I.e., it will not regain magnetism when it cools down, and attempts to re-magnetize it may fail.
What is Neodymium Magnet Curie Temperature? (Concept)
Neodymium magnets’ curie temperatures are graded like maximum operating temperature, using letters after the neodymium magnet’s grade.
Neodymium magnets are popular due to their strength and durability. They can function for a long time and still not lose their magnetism.
What is the Curie Temperature of Neodymium Magnets?
Below are the Curie temperatures for each neodymium magnet grade. Heating a neodymium magnet above its Curie temperature will make it lose its magnetic force permanently.
| Grade | Celsius | Fahrenheit |
|---|---|---|
| N | 310°C | 590°F |
|
M |
340°C | 644°F |
| H | 340°C | 644°F |
|
SH |
340°C | 644°F |
| UH | 350°C | 662°F |
|
EH |
350°C | 662°F |
| TH/AH | 350°C | 662°F |
What Happens When You Exceed the Curie Temperature of Neodymium Magnets?
Heating neodymium magnets to high temperatures will mess with their atom cohesion, causing a disturbance in their magnetic domains. This disturbance weakens their magnetism as the heat rises.
When you exceed neodymium magnets’ curie temperature, they will permanently lose their magnetism.
The Relationship between the Two neodymium magnet temperature
Max Operating and Curie temperatures are related because they indicate the heat levels that affect a neodymium magnet’s performance.
However, while the MaxOpTemp will only cause an irreversible loss in neodymium magnets, reaching their curie temperature will cause permanent loss.
Operating Temperature & Curie Temperature（Grade N, Grade M, Grade H, Grade SH)
|
Grade |
Max Operating Temperature | Curie Temperature |
|---|---|---|
| N | 80°C or 176°F | 310°C or 590°F |
| M | 100°C or 212°F | 340°C or 644°F |
| H | 120°C or 248°F | 340°C or 644°F |
| SH | 150°C or 302°F | 340°C or 644°F |
| UH | 180°C or 356°F | 350°C or 662°F |
| EH | 200°C or 3922°F | 350°C or 662°F |
| TH/AH | 220°C or 428°F | 350°C or 662°F |
Does Temperature Affect Magnets?
Neodymium Magnets Experience Three Types of Performance Losses at High Temperatures.
When you expose neodymium magnets to high temperatures, they experience one of 3 performance losses: reversible, irreversible, and permanent.
How Does Temperature Affect Magnets? Or How Temperature Affects Magnets?
Reversible Loss (Operating Temperature)
Reversible loss refers to the reduction in magnetic strength a neodymium magnet experiences when it reaches a very high temperature close to its maximum operating temperature level.
When the neodymium magnet cools to room temperature, its magnetism will return. It will be just as strong as it was before. Thus, the magnetism loss is reversible.
Irreversible Loss (Between Operating Temperature & Curie Temperature)
Irreversible loss of magnetic strength happens when a neodymium magnet is exposed to higher temperatures than its maximum operating temperature but lower than its curie temperature.
When this happens, the neodymium magnet cannot return to its original strength even after it cools down. It will have some magnetism left in it. However, its performance will no longer be what it used to be.
Permanent Loss (Exceed Curie Temperature）
Permanent loss of magnetic field will occur in a neodymium magnet if you heat it to its curie temperature.
For a neodymium magnet, experiencing permanent loss is a point of no return because no hint of magnetism will be left in it after it reaches its curie temperature.
Neodymium magnets that suffer permanent loss after reaching their curie temperature cannot regain their magnetism, no matter how much you try to re-magnetize them.
Neodymium Magnet (Magnetic Characteristics, Demagnetization Curve)
Regarding neodymium magnets, their heat resistance is not the only important thing. Their magnetic characteristics and demagnetization curve are equally important.
Magnetic Characteristics (Grade Include Br Hcb Hcj BHmax)
The magnetic characteristics of neodymium magnets include Remanence, Coercive field, Intrinsic coercive force, and Max energy product.
| Characteristics | Meaning |
|---|---|
|
Remanence (Br) |
Remanence, or retentivity, is the ability of a neodymium magnet to keep magnetic power after the reduction or elimination of magnetization. Remanence allows neodymium magnets to retain magnetic force during magnetization. |
|
Coercive field (bHc) |
Refers to a magnetic material’s measure or ability to resist demagnetization from an external magnetic field. The higher this value, the better it will perform against demagnetization forces. |
|
Intrinsic Coercive Force (jHc) |
This indicates the strength of the magnetic field required to bring the power of magnetization to zero. Neodymium magnets with low intrinsic coercive force may irreversibly lose magnetic strength. |
|
Max Energy Product (BHmax) |
The BHmax is the highest point on a magnetic demagnetization curve. It represents the maximum energy density a neodymium magnet can hold. In neodymium magnets, BHmax will typically range from 30 to 55 MGOe. Their strength depends on how high the BHmax is. |
Demagnetization Curve
The demagnetization curve is a chart describing a neodymium magnet’s magnetic qualities. The demagnetization curve indicates the strength of a neodymium magnet. Its basic shape and demagnetization difficulty. The demagnetization curve, i.e., the second quadrant, defines the parameters Br, bHc, jHc, µr, and (BH)max.
The different parts of the demagnetization curve include
| Normal Distribution | Describes the neodymium magnet’s performance. |
|---|---|
| Intrinsic Curve | Mean the neodymium magnet’s properties when there’s no air gap between poles. |
| Load Line | Also known as the operating line, you draw it from zero to the Permeance Coefficient of your neodymium magnet. |
| Operating Point | The intersection of the Load Line and the Normal Curve. |
What are the Melting Point and Boiling Point of Neodymium Magnets?
Neodymium on its own has a melting point of 1861°F (degrees Fahrenheit). However, neodymium magnets comprise several other materials. They didn’t melt down completely when we exposed them to 2,500°F (enough to melt steel). So you will require more than 2,500°F to melt neodymium magnets to the boiling point.
Neodymium magnets react differently to temperatures high enough to melt them down. For instance, neodymium magnets behave like steel and melt into liquid.
Ferrite or Ceramic magnets, on the other hand, don’t like heat, and they would blast into pieces as soon as they get hot. However, if you do manage to melt a ferrite magnet, it would harden faster than a neodymium magnet would.
Effective Methods to Prevent High-Temperature Demagnetization of Neodymium Magnets
High temperature is one of the top causes of demagnetization in permanently magnetized materials like neodymium, samarium cobalt, and Alnico magnets. You can prevent high-temperature demagnetization of neodymium magnets if you:
- Keep them away from heat at all costs.
- Don’t expose them to heat above their MaxOpTemp.
- Avoid heating neodymium magnets up to their curie temperature.
Examples of Neodymium Magnets that Can Withstand High Temperatures
There are several grades of high-temperature neodymium magnets. They have different magnetic strength and magnetic coercivity levels, i.e., the neodymium magnet’s ability to resist Degaussing.
We use a popular lettering system to grade neodymium magnets when dealing with permanent magnets. The following letters indicate their highest working temperatures:
| Grade | MaxOpTemp |
|---|---|
|
TH/AH |
This is currently the highest neodymium magnet grade available. Any neodymium magnet that has TH or AH after the grade number, i.e., N52AH, will typically have a MaxOpTemp of 220°C to 230°C or 428°F to 446°F. |
|
EH |
The EH grade comes immediately after the TH/AH rating. With a difference of 20-30°C in max working temperature, a neodymium magnet with this rating will have a max operating temperature of up to 200°C or 392°F. |
|
UH |
The UH grade goes down to 180°C or 356°F max operating temperature. |
|
SH |
The SH grade is the starting point for neodymium magnets under the high-temperature class. These neodymium magnets typically have a MaxOpTemp of 150°C or 302°F. |
About High-temperature Demagnetization
High-temperature demagnetization is when neodymium magnets lose their magnetic abilities after exposure to very high temperatures. It happens faster if the heat is more than their maximum operating temperature.
It may occur in a lab, under controlled conditions, or in the field, where there is no control over the process.
Principle
- Below the max operating temperature, the magnetic force of the neodymium magnet and temperature share an inverse relationship; as one decreases, the other increases. However, the magnetic force will return after the neodymium magnet cools down.
- A neodymium magnet will lose its magnetic force if heated within the MaxOpTemp and the CurieTemp. Some magnetism will rehabilitate when cooled, but it will not function like it used to.
- Suppose a neodymium magnet is heated to the Curie temperature or heated for a long time above the MaxOpTemp. In that case, it will permanently and irreversibly demagnetize.
- If a neodymium magnet is demagnetized after losing its magnetization, it cannot restore its performance to what it was.
High-temperature Demagnetization Equipment
To demagnetize neodymium magnets using heat, you can use any equipment capable of generating very high heat levels. These include
- A Furnace.
- A Foundry.
- An Oxyacetylene torch.
- An oven.
How Long will High-temperature Demagnetization Take?
How long it will take to demagnetize a neodymium magnet using heat varies, depending on the grade, the size, the composition of the alloy, and the amount of heat supplied to it.
However, if you heat a neodymium magnet to its Curie temperature, it will suffer permanent demagnetization immediately.
Can Neodymium Magnets be Re-magnetized After Being Demagnetized at High Temperatures?
It is possible to re-magnetize a neodymium magnet that has suffered an irreversible loss due to high-temperature demagnetization. However, recovery is impossible if the neodymium magnet loses its magnetic force permanently.
Where to Get Quality Neodymium Magnets?
You can safely procure quality, ISO 9001:2015 certified neodymium magnets from ROBO Magnetic.
With over a decade and a half of experience in the industry, we are one of China’s leading producers and suppliers of neodymium magnets to the international market. Contact our team to discuss your requirements and how we can assist you.
