Neodymium magnets: a complete guide for beginners

From the industrial revolution to the present day, magnetism has been an essential force in technological development. Among the different types of magnets, neodymium magnets stand out for their incredible power and versatility. These small but powerful devices have changed how many industries operate, from automotive to electronics and medicine. They have even influenced art sectors such as modeling, where they are used to keep miniature bases steady on some surfaces, articulate the limbs of miniatures, or create detachable dioramas, among other things.

In this article, we will explore in detail what they are, how they are manufactured, their various applications, and everything you need to know about their properties and uses.

What is a neodymium magnet?

A neodymium magnet, NdFeB magnet, or rare earth magnet is a type of super-powerful permanent magnet made from an alloy of neodymium, iron, and boron (NdFeB). They are the most powerful commercially available and are used in a wide variety of applications due to their extraordinary magnetic strength in comparison to their size. They were developed in the 1980s by General Motors and Sumitomo Special Metals, and have since revolutionized the magnetic industry.

They stand out for their high remanence and coercivity, which means that they maintain their magnetism for long periods and are difficult to demagnetize. However, their fragility and susceptibility to corrosion require them to be coated by Ni, zinc, or epoxy to improve their durability. They are used in electric motors, generators, hard drives, medical equipment, and more.

How are neodymium magnets made?

The manufacturing process is complex and involves several stages. First, the base materials (neodymium, iron, and boron) are mixed in precise proportions to obtain the optimal combination that gives future pieces the highest magnetization. Then, the resulting alloy is cooled in a special oven, without oxygen and with a special gas to prevent the metals from oxidizing. When the alloy has cooled and hardened, it is ground into a very fine powder to ensure that the elements are evenly distributed for a better structure of the neodymium magnet, and then compacted into the mold that will give the magnet its shape. To compact it, a magnetic field is used in a special press for this purpose. This is the key to making it denser, which translates into more atoms of the three materials in each piece.

Then, all these pieces undergo a sintering process, that is, they are heated almost to the point of melting, which causes the particles to stick to each other, making the product more compact and resistant to sintering and heat in general. Now, it goes through a magnetization process to activate its magnetic properties, placing the pieces in a very strong external magnetic field that aligns the neodymium, iron, and boron atoms creating a permanent magnet. The final strength is determined by the magnetic field used.

Finally, they are protected with a layer of nickel, zinc, chromium or epoxy resin to prevent water, oxygen, and other agents from corroding the magnet or damaging it in other ways.

What is a Nd magnet​ used for?

Neodymium magnets have a wide variety of applications due to their extreme power and durability. One of their most common uses is in high-performance electric motors, such as those used in electric vehicles, drones, and industrial tools. They are also found in renewable energy generators, advanced electronic devices, in the medical industry, toys or scientific experiments. Specifically, they are used in:

• Automotive. They are essential in sensors, electric motors, alternators and regenerative braking systems in hybrid and electric vehicles. They are also used in automatic door closers and sound systems.

• Pumps, fans, turbines, and renewable energy generators with wind turbines.

• Electronic devices. In hard drives, mobile phones, headphones, speakers, microphones, among others. They improve sound quality and storage performance.

• Lighting systems. They are used to hold and adjust lighting panels without the need for screws or adhesives. In LED lamps and directional spotlights, they allow for quick changes in orientation and mounting.

• Metallurgical industries. They are used in systems for collecting metal particles, lifting magnets for handling heavy parts, and in the manufacture of magnetic tools.

• Construction. In construction, the Nd magnet​ is used to fix metal panels, level structures, and precisely align prefabricated elements.

• Medical devices. They are used in magnetic resonance imaging (MRI), insulin pumps, and rehabilitation devices, enabling more advanced diagnoses and treatments.

• Magnetic lifters. They allow heavy loads to be handled without physical contact, reducing wear and improving efficiency in warehouses and factories.

• Magnetic levitation. Used in maglev trains and in scientific experiments to create frictionless forwarders.

• Magnetic motors. Found in high-performance, low-friction motors used in robotics, power tools, and electric vehicles.

• Food industries. The Nd magnet​ is used in metal detectors and magnetic separators to eliminate metal particles from food during processing, guaranteeing food safety.

• Plastics industries. In these industries, NdFeB magnets are used in magnetic separators that remove metallic impurities from recycled plastic. They are also useful in molds and magnetic clamping systems to facilitate manufacturing processes.

• Furniture industry. They are used in the furniture industry to create magnetic closures on cupboard doors, drawers, and display cabinets. They are also used in screwless fastening systems, allowing for a cleaner, more minimalist design.

• Magnet fishing. It is a recreational activity where the Nd magnet​ is used to retrieve metal objects from rivers, lakes, and seas.

• Hobby and modeling. They are popular in the construction of models, action figures, miniature trains, RC body magnets, and other projects to facilitate the assembly of bases or movement trays and other detachable elements.

Why are neodymium magnets so strong?

Their incredible strength is due to their atomic structure and the combination of a specific amount of neodymium, iron, and boron. This allows for a strong alignment of the magnetic dipoles, which generates an extremely powerful magnetic field. In addition, they have a high remanence, which means they retain their magnetism for long periods without needing an external energy source.

Another key factor is their high coercivity, which allows them to resist demagnetization even in adverse conditions. Their power far exceeds that of a permanent magnet of another type, such as ferrite or alnico, making it the preferred choice for applications where high magnetic strength is required in a compact size.

How long do neodymium magnets last?

They can last decades if they are kept in the right conditions. Under normal use, they lose less than 1% of their magnetism in 100 years, which makes them practically permanent for most applications. Their longevity depends on factors such as the temperature to which they are exposed, the presence of humidity and mechanical shocks that can fracture them.

However, if they are subjected to high temperatures above their Curie point (around 310-400 °C, depending on the grade), they can lose their magnetism irreversibly. They can also deteriorate if they do not have a suitable coating, as exposure to moisture can cause oxidation and structural degradation.

Are neodymium magnets safe?

NdFeB magnets are not toxic, but they can be dangerous if not handled correctly. Due to their high magnetic force, they can pinch the skin or cause serious injury. If two of these pieces get too close, they can be attracted with considerable force and break into sharp fragments that can cause injury.

In addition, they come in various sizes, from one millimeter to several centimeters, the most common, so they represent a significant risk for ingestion, especially in children. If a person swallows two or more pieces, they can join together inside the digestive system, causing blockages or serious intestinal perforations. For this reason, some of these products have been restricted or regulated in many countries.

Other frequently asked questions about Nd magnet​s

• What are neodymium magnets made of?

They are usually a mixture of neodymium, iron and boron, with a final coating of another element to protect it from corrosion and oxidation, keeping it away from moisture and oxygen in the air.

• Do neodymium magnets rust?

Yes, they are highly susceptible to oxidation and corrosion. To prevent this, they are usually coated by one or more layers of Ni, copper, epoxy resin and other components. This coating protects them from oxidation and possible impacts. However, if it becomes damaged or worn, the magnet will be unprotected and may rust.

• Can the Nd magnet​ damage cell phones?

Yes, they can affect some electronic components that are sensitive to magnetic fields, interfering with the readings of the digital compass and the phone's magnetic sensors. In addition, they can damage other devices that work with magnetic elements such as credit cards or hard drives, if placed too close.

• Can you bring neodymium magnets on a plane?

Yes, but with limitations. They are regulated by IATA regulations, so depending on the quantity and size they can be classified as dangerous goods. They must be packed according to the specifications of these regulations to guarantee interference with navigation instruments. It is always advisable to consult with the airline before forwarding them.

• Do rare earth magnets wear out?

They do not wear out with use, but they can lose strength if exposed to high temperatures, strong shocks, or corrosion if the protective layer is damaged.

• What temperature do they, lose their magnetism?

Above 80 °C some NdFeB magnet can start to lose magnetism. Neodymium sheets and magnetic tapes, from 85 ºC. If they exceed 310-400 °C (depending on the type), demagnetization is irreversible. A ferrite magnet, on the other hand, withstands temperatures of up to 250 ºC without demagnetizing.

• Are all magnets neodymium​?

No, there are other types such as ferrite (ceramic), alnico and samarium-cobalt:

• Ferrite (ceramic). It is composed of iron oxides and other metals. It is less powerful but more economical and resistant to corrosion, which is why they are used in speakers, electric motors, and magnetic locks.

• Alnico. These are made from aluminum, nickel, and cobalt, and are highly resistant to extreme temperatures. They are used in measuring instruments, sensors, and industrial motors.

• Samarium-cobalt. These super-powerful rare earth magnets are similar to neodymium magnets but with greater thermal and corrosion resistance. They are used in aerospace, military, and medical applications where powerful and long-lasting pieces are required.

• Flexible ones. These are made of plastic or rubber mixed with ferrite powder, which makes them flexible. They are used in magnetic tags, advertising, and fridge seals.

• Electromagnetic. Unlike permanent ones, these generate a magnetic field only when an electric current passes through them. These are the ones that are incorporated into industrial cranes, maglev trains, and medical devices such as magnetic resonance imaging.

• Can a Nd magnet​ conduct electricity?

A Nd magnet​ is not a good electrical conductor, although it does have some conductivity due to its metal content.

• How much are neodymium magnets?

It depends on their size and power, but they tend to be more expensive than ferrite ones due to the materials used in their manufacture. The smallest can cost a few cents or penies each (they usually come in packs) and the largest hundreds of euros.

• Is an Nd magnet​ food safe?

No, an NdFeB magnet is not considered food grade, it is not designed to come into direct contact with food, as it can release heavy metal particles if its coating is damaged.

For applications in the food industry, a super-powerful Nd magnet​ with specific coatings approved for food contact, such as food-grade stainless steel, is recommended to guarantee safety and prevent contamination.

• Are neodymium magnets illegal​?

No, although in some countries their sale is regulated to avoid accidents, especially in children's toys.

• Are they permanent?

Yes, NdFeB magnets are permanent, which means that they retain their magnetism indefinitely under normal conditions of use. They can only lose their strength if they are exposed to high temperatures, strong shocks, or intentional demagnetization employing an opposing magnetic field.

• Are NdFeB magnets radioactive?

No, they are not radioactive. Despite being a rare earth material, they do not emit radiation and are safe for use in industrial, medical, and domestic applications.

• Are neodymium magnets the strongest?

Yes, they are the strongest commercially available. They have a higher magnetic force than other types of magnet, such as ferrite or alnico, which makes them ideal for applications that require high power in a compact size.

• Can they be drilled?

Drilling or sawing neodymium magnets is not recommended, as they are fragile and can easily break during the process, as well as lose part of their protective coating. By the way, the heat generated by drilling can demagnetize them and this process would generate flammable dust. In the same way, they cannot be soldered, as the extreme heat of the soldering can demagnetize them and damage their structure.

• Can they pick up coins?

An Nd magnet​t can only attract coins containing ferromagnetic metals, such as iron or nickel. Many coins are made of other non-magnetic metals, such as copper or aluminum.

• Does Nd magnet​ remove security tags?

Some security tags use magnetic mechanisms, so they can interfere with them. However, tampering with security tags without authorization is illegal.

• Do they break easily?

Yes, despite their high magnetic strength, NdFeB magnets are fragile and can break or chip if it is hit or dropped on a hard surface.

• Do they have a north and south pole?

Yes, like any magnet, neodymium magnets have a north and a south pole. The orientation of these poles determines how they interact with other pieces and magnetic fields. Therefore, they also repel each other if they face the same pole (north with north or south with south) due to the nature of magnetic fields.

• How to glue neodymium magnets?

Strong adhesives such as epoxy or cyanoacrylate are recommended. Before sticking them to a surface, it is important to make sure it is dry and clean to achieve a long-lasting bond.

• How strong is neodymium magnet?

It depends on the size and grade of the piece. Some can support a few grams, while larger ones can lift tens or even hundreds of kilograms.

One of the clearest indicators of the power of an Nd magnet​ is its grade, which indicates the strength that its magnetic field can generate. This classification is represented by an “N”, followed by a number (for example, N35, N42, N52). The number refers to the “maximum energy product” of the piece, measured in Mega Gauss Oersteds (MGOe). Therefore, the higher the number, the stronger it is. For example, an N42 is stronger than an N35. There is a table with the standardized values for each grade of magnetic material, where you can consult the numerical values of: Remanence (Mr), Coercivity (Hci), and Maximum Energy Product (BHmax). Currently, the highest grade manufactured is N35, and the most common are N35, N38, N40, N42, N45, N48, N50, N52.

Although it is not common to find other grades on the market, there are custom neodymium magnets, but they tend to require more complex and costly manufacturing processes. In addition, it should be emphasized that size and shape are factors that influence their strength. On the other hand, depending on the manufacturing method and the products used, they may have a higher or lower resistance to heat, an important factor for several industries.