Did you know Neodymium is a generally used magnet you come across daily? It is used in headphones, computer hard disks, generators, and electric motors. Another important fact about this magnet type is its existence as the strongest permanent yet discovered.
Neodymium magnet is an alloy made from rare-earth metal. Neodymium, iron, and boron (NdFeB) are the primary metals with traces of praseodymium (Pr), Dysprosium (Dy), aluminum (Al), and niobium (Nb).
To find out more about the composition of this magnet, its properties, and its strength, continue reading, and I’ll surely share some valuable and worth-reading information. Let’s do it:
Constituents of NdFeB magnet
Also known as the rare earth magnet, NdFeB magnets are made of three prominent rate earth metals, Neodymium, iron, and boron. Physically, the structure of the Neodymium crystals is tetragonal crystalline.
As it is an alloy of metals, different companies constituted it commercially. General Motors and Sumitomo Special Metals developed the alloy independently, and the purpose of its creation was its use for commercial purposes.
History of Neodymium magnets
The history of the NdFeB magnet is just a few decades long. The motive behind creating this Neodymium magnet was to find an alternative for the high cost of raw material associated with the magnet widely used at that time, i.e., SmCo.
Although the effort to start this powerful magnet’s manufacturing process started simultaneously, the type of process adopted for this purpose differed. GM produced melt spun Nano crystalline Nd2Fe14B magnets, while Sumitomo developed sintered or full-density Nd2Fe14B magnets.
After two years of the initial effort from the two companies, GM patented its new isotropic patent and the related production process. The result of this process was the melt-spun powder to magnet manufacturers.
Hitachi bought the company to which the GM supplied melt spun isotope. Now Hitachi covers 600 patents related to Neodymium magnets. Because of these patents adopted by Hitachi, most rare energy metals are part of the Chinese market. Considering it, the Department of Energy USA is funding research to look for new rare earth metals.
One of the primary uses of these powerful magnets is in wind turbines. China’s company holds most of the patents to these metals, so the search for an alternative to these metals is of utmost priority.
Why Neodymium magnets are considered rare earth magnets?
The association of Neodymium to the rare earth magnet family is because of the presence of rare earth metals in its formation.
The rare in the description of this magnet doesn’t signify the scarcity of the metal. Neodymium is present in the Earth’s crust and is in abundance. So, what does the rare mean? It is associated with geochemical properties. All the rare earth metals, including Neodymium, are present in the dispersed form in the Earth’s crust; thus, finding it from the commercial perspective is highly expensive.
What gives strength to the NdFeB magnet?
Neodymium has magnetic properties of its own in its pure form. But the magnetism is only applicable at a specified temperature range below 19 K (−254.2 °C; −425.5 °F). However, it is imperative to add transition metals such as iron to give Neodymium magnetic properties at average room temperature.
Considering the magnet’s strength, several factors come into play, like structure.
The tetragonal crystal structure is vital in providing strength to the magnet, and this crystalline structure highlights its properties to magnetize along the crystal axis. When it is converted to the alloy form, the microcrystalline grains align with the other materials in the same direction, offering it strength.
With the strong magnetic field created, the lattice formed resists turning away from the existing direction to the other; thus, the compound has a high coercively and higher resistance to demagnetization.
Moreover, in the Neodymium magnet, the vital dipole moment due to 4 unpaired electrons also gives strength to the magnet. The unpaired electrons align on the same axis as the magnetic field, thus creating an even magnetic solid power.
Other factors contributing to the strength of the Neodymium magnets are the microstructure, alloy composition, and the manufacturing used to create these metals.
How are Neodymium magnets created?
Neodymium is an alloy of rare earth metals, so it has to be created with a combination of a few primary and secondary elements. The addition of the secondary elements in the making enhances specific properties of the magnet, including temperature tolerance, strength, anti-corrosion, and resistance to demagnetization.
There can be different forms of the magnet created using multiple other mechanisms. The general creation of these magnets includes melting the metals with a vacuum induction furnace. We use the strip casting method to cool the molten metal. With this rapid cooling method, the molten metals turn into flakes form.
To break down these flakes, a jet mill comes in handy. With the jet mill, the flakes are crushed into a fine powder.
As I already highlighted, there are a few changes in the methods of creating a Neodymium magnet that gives different forms of the magnet that we know today! So, I’ll highlight the process involved in each of them.
Sintered Magnets
Neodymium, iron, and boron are the primary metals in the production process that are melted in a furnace. With the addition of different primary metals, the manufacturers adjust the chemical composition of the magnet to ensure the right Curie point, coercivity, and flux density.
After the completion of the melting process, it is cooled and turned into the form of flakes. With the help of a jet mill, the flakes are broken into fine powder.
The fine powder is pressed into a shaped mold in the sintered magnet category. The magnetic energy used to heat the powder is the shaped mold again, resulting in dense blocks forming. The magnet produced as a result of this process is anisotropic. It means that the magnetism direction of this magnet aligns with the particle structure, and such a condition is achieved by applying the external magnetic field.
Once the direction of the magnetic is locked through the magnetic field and the material is demagnetized, the sintering stage comes from where the name of this particular magnet type is derived. In this process, the dense block of magnet formed ta the last step is heated in an oxygen-free environment at a temperature close to its melting point.
The purpose of this step is to fuse the magnetic particles. It is then rapidly cooled to a specific temperature, resulting in more strength and hardness. It is then reheated and cooled again. Once these steps have been applied to the metals, they can be converted into the appropriate shapes according to the intended usage. Diamond-plated cutting tools and electrical discharge machining help in the process.
If you have been wondering about the reason for heating and rapid cooling involved in the process, then you must know that it is not just another step in the process; instead, the performance of rapid cooling eliminates the areas of poor magnetism and the final product you get is the sintered magnet.
Bonded Magnets
One of the things different between the bonded magnets and the other magnets type is the raw material. Although rare-earth metals are the bonded magnet’s significant constituents, there is an additional binder in the process.
In this process, the NdFeB alloy is converted into powder form and mixed with a polymer. Although it is an essential part of the raw material in many products, its use as a standalone magnet isn’t worth enough.
One reason for its lower strength and magnetic properties is that it contains lesser Neodymium and higher iron. There are multiple methods for creating bonded magnets, amongst which injection molding is one.
In this method, a thermoplastic compound is used. It is injected into a mold with a magnetic NdFeB powder as a magnetic agent and then cooled. Once it takes the shape of the mold, it is ready to use. The entire exercise aims to add more magnetic properties to the raw material and convert it to the right shape.
Extrusion, calendaring, and compression bonding are a few other methods of performing this technique and the creation of bonded magnets.
Usually, such magnets are part of toys, brushless motors, speakers, and buzzers.
Protective Coating
Neodymium magnets can break and oxidize quickly, making them vulnerable to the environment. Not all neodymium magnet types are used as raw materials, so they have to be made more robust than their original form, which means they need a protective layer.
The coating is often made of the metals like nickel and copper. Another exciting thing is that a single layer of coating wouldn’t be enough. Three layers are electroplated on the magnet to give it the right cover and protection.
The coating application ensures that the magnet’s life can be prolonged. Another thing to note while applying the protective coating is that the electroplating process must initiate before the magnet is magnetized; otherwise, the magnetic field of the magnet will disrupt electroplating, and the desired results wouldn’t be achieved.
Nickel-copper-nickel mixture is the most common electroplating mixture, but PTFE polymers can also be applied as the protective layer.
The process of adding a protective coating is a bit different for the bonded magnets. In this process, these magnets are provided with an Electrophoresis Coating (“E-coating”) or Spray Coating process.
Using E-coating is preferred because it has a uniform thickness and works well in multiple scenarios, thus not hindering the overall utility of the bonded magnets. Spray coating works well with smaller magnets but isn’t appropriate for larger ones.
Properties of neodymium magnet
Neodymium magnet has some distinct properties. Let’s have a quick overview of these properties to know the powerful rare earth magnet in detail:
Grades
Magnets are categorized according to their grades. The grade depends upon the maximum energy product produced by the magnet, and it is calculated as the magnetic flux output per unit volume.
A higher answer to this calculation indicates a stronger magnetic field, while a lower one indicates a weaker magnet. All these calculations with different combinations are conducted in advance as the international classification. Considering the Neodymium magnet, the international classification categorizes the values between 28 to 52.
Following are the primary grades of sintered NdFeB magnets.
- N30 – N55
- N30M – N50M
- N30H – N50H
- N30SH – N48SH
- N30UH – N42UH
- N28EH – N40EH
- N28TH – N35TH
The N in the grading above indicates a neodymium magnet, and the letter after the numbers indicate intrinsic coercivity and maximum operating temperatures.
Physical and mechanical properties
In this section, I have highlighted the values associated with the different physical properties of the Neodymium magnets:
| Property | Neodymium |
| Remanence (T) | 1–1.5 |
| Coercivity (MA/m) | 0.875–2.79 |
| Recoil permeability | 1.05 |
| Temperature coefficient of remanence (%/K) | −(0.12–0.09) |
| Temperature coefficient of coercivity (%/K) | −(0.65–0.40) |
| Curie temperature (°C) | 310–370 |
| Density (g/cm3) | 7.3–7.7 |
| Thermal expansion coefficient (parallel)(1/K) | (3–4)×10−6 |
| Thermal expansion coefficient, (perpendicular) (1/K) | (1–3)×10−6 |
| Flexural strength (N/mm2) | 200–400 |
| Compressive strength (N/mm2) | 1000–1100 |
| Tensile strength (N/mm2) | 80–90 |
| Vicker |
Magnetic properties
Certain concepts and terms are used to describe the strength of the magnet, and I’ll discuss them with an explanation of each of these terms so you can understand them better.
- Remanence (Br) – measures the strength of the magnetic field.
- Coercivity (Hci) – its resistance to being demagnetized.
- Maximum energy product (BHmax) is the density of magnetic energy. The calculation of the maximum energy product is based on the magnetic flux density and time’s its magnetic strength
- Curie Temperature (TC) is the temperature where magnetic properties no longer remain
These magnets have higher remanence and coercivity based on these magnetic properties. However, the Curie temperature is lower. The changes in the form of secondary metals added into the alloy formation stage help increase the curie temperature of the Neodymium magnets.
Corrosion
The sintered variety of the magnet is highly prone to corrosion. Usually, the boundaries of the magnet are expected to witness this phenomenon. This corrosion can be seen in the crumbling of the magnet into powder or the erosion of a surface layer.
A protective layer of nickel is added to the magnet to protect these magnets from corrosion. It keeps the neodymium magnet in its real shape for a longer time. Besides, it makes the magnet available to be used directly with environmental factors, which otherwise wouldn’t be possible.
Temperature resistance
The Neodymium magnets cannot withstand extremely high temperatures because of the negative temperature coefficient. In extreme temperatures, the lack of temperature resistance limits its efficiency.
Terbium and Dysprosium are added to the alloy to make it more efficient. It enhances the temperature tolerance of the magnet but simultaneously increases the cost significantly, making it problematic for commercial usage.
Hazards
The strong magnetic force can create hazards, which are not often cared for when people are close to the other magnet types.
- Pinching: neodymium magnets over a few cubic centimeters can pinch the skin when it comes in between two magnets. You can expect effects as strong as broken bones.
- Eye injuries: two magnets striking with force can cause enough force to shatter each other. The small pieces broken and spread in the environment can create eye injuries
- Mistake swallow: engulfing the neodymium metal pieces by children is another cause of concern. A few injuries and deaths have been reported where swallowing two or more pieces of Neodymium magnet resulted in pinching of the digestive tract.
- Erase the magnetic data: even from a significant distance, you can expect these magnets to erase the magnetic data stored in the floppy disk, credit cards, and CRT monitors.
- Health risks: People working close to the machines with these strong Neodymium magnets can cause serious health risks.
- Fire: as these magnets are capable of chipping, striking these chips can cause a fire. The interaction of the flying chips creates sparks like a lighter flint. If the environment is capable of catching fire, it can cause severe damage to the property, people, and environment around it.
The robust nature of these magnets requires the users to be very careful when around them or using them for different commercial purposes.
Where can Neodymium Magnet use?
Neodymium magnets have a wide range of applications. Usually, they are used in modern technology. There are a few industries where the alternate magnets were in use, but after the discovery of neodymium magnets, these magnets are considered to be the best available utility.
This is why I have divided this section into two separate sections:
Currently explored
The current magnet usage includes hard disks, e-cigarettes, loudspeakers, headphones, door catches, magnetic bearings, electric motors, electrical generators, wind turbines, decouplers, and many others.
New application
As the Neodymium magnet is considered the most potent magnet discovered till now, its applications are ever-evolving, with new research studies being conducted to analyze the strength of its capability to be used in different industries.
Some research worlds in this context include magnetic jewelry, children’s magnetic building sets, and other children’s toys. The strength of this magnetic type is high, which means the minimal use of these magnets will reduce the hazards that might come with the magnet’s power.
Apart from the general usage of these magnets in daily use, research is also being conducted in the medical sciences. An open magnetic resonance imaging (MRI) technique is being analyzed using a strong magnet to get the body image in the radiology department.
These magnets are also used in the digestive tract to control the anti-reflux in gastroesophageal reflux disease (GERD). Also, magnetic implants by biohackers in the fingertips have been done to field the magnetic force within the tips of the fingertips.
Difference between neodymium magnets and samarium magnets
Both Neodymium and samarium are types of rare earth magnets. However, both of them portray different qualities with a few similarities. By reviewing the similarities and differences between the properties of both these magnets:
Corrosion resistance:
Neodymium is a high-corrosion magnet that requires extra protection or coating over it, while samarium is highly resistant to corrosion and can work without requiring any additional steps.
Temperature tolerance:
Neodymium rare earth magnet is moderately resistant to the temperature, whereas samarium is highly resistant. The exact understanding of a Neodymium magnet’s ability to withstand temperature can be attributed to its grade.
Cost:
From the cost perspective, the cost of the Neodymium magnets is much lower than the available samarium variety.
Difference between Neodymium magnets and other regular magnets
The difference between Neodymium and regular metals is highlighted below to help you understand the strength of this particular metal type:
Metal composition:
The Neodymium rare earth metal is formed of Neodymium, Iron, and boron, whereas the composition of the regular magnets is iron oxide, barium, manganese, nickel, and zinc.
Energy and magnetic field:
The magnetic field generated by a Neodymium magnet is strong, with an overall high energy inherent in the metal. The other regular magnets have a weaker magnetic force with low energy.
High coercive force:
The coercive force exercised by the Neodymium magnet is high, and it is because of the strong magnetic field present in the metal, whereas regular metals have a weak coercive force.
Frequently Asked Questions (FAQs)
Why are Neodymium magnets coated?
Neodymium magnets have high corrosive properties, eroding the magnet’s sides when in use. An extra coating or protective layer is added during the formation process for its proper maintenance and long-term life. It helps make the Neodymium magnets better and easily usable when in direct contact with the environment.
Can Neodymium magnets become weak over time?
Yes, Neodymium magnets can lose their strength after some years. However, the decrease in their magnetic properties is not excessively high, and they only lose 1% of their power in 10 years. You can easily exact them to be functional for centuries with this capacity.
What is the strong magnet in the world?
Without any doubt, Neodymium is the strongest magnet in the world.
Why are Neodymium magnets in hype?
The hype of the Neodymium magnets is associated with their strength; they are the strongest and commercially viable magnet yet discovered.
Can Neodymium magnets be used in children’s toys?
Although these magnets are strong, they can be sued in children’s toys and other household items in minute sizes.
Is the magnetic field created by a Neodymium magnet dangerous?
The magnetic field isn’t dangerous for humans; however, the interaction with the metals might be hazardous if not handled properly.
On the other hand, the magnetic field can be dangerous to different magnetic items like floppy disks and hard drives.
Where should you not put the Neodymium magnets?
The strength of the magnetic field makes them inappropriate to be used near media devices because the magnetic field created by these magnetics can destroy the data in them and even the electronics.
Conclusion
Neodymium magnets are the most powerful rare earth metals discovered yet. They are made from a combination of Neodymium, boron, and iron with an amalgamation of other secondary metals to give them different properties depending upon their application.
Because of its strength is used in different medical and renewable energy resources and has daily household utilities. Irrespective of its positives, serious hazards are involved with its usage that demands extreme care.
