Neodymium Magnets: Applications and Properties

Chapter One – Understanding Neodymium Magnets

Neodymium magnets, often abbreviated as Nd-Fe-B magnets, are highly powerful rare earth magnets crafted from an alloy that includes neodymium (Nd), iron (Fe), boron (B), and additional transition metals. They are renowned for their remarkable magnetic field intensity, reaching up to 1.4 teslas (T), which enables exceptional performance across numerous applications due to their significant magnetic flux density.

The manufacture of neodymium magnets involves two primary techniques: sintering and bonding. Since their debut in 1984, these magnets have dominated the market as the most prevalent type due to their impressive strength and efficiency.

In its pure state, neodymium is ferromagnetic, but it only becomes magnetized at temperatures that are exceedingly low. However, when alloyed with metals like iron, neodymium achieves magnetization at room temperature.

The category of rare earth magnets includes neodymium and samarium cobalt types. Before neodymium magnets revolutionized the industry, samarium cobalt magnets (SmCo) were predominant. However, neodymium magnets have largely replaced them due to the high costs associated with producing samarium cobalt magnets.

Despite being less potent than neodymium magnets, samarium cobalt magnets boast a greater tolerance for high temperatures and excellent corrosion resistance, making them ideal for tough environments and situations where robustness is a priority.

Chapter Two - What are the Properties of a Neodymium Magnet?

Neodymium magnets, often referred to as NdFeB magnets or rare earth magnets, are renowned throughout the magnet industry for their outstanding magnetic strength and compact size. As the strongest type of permanent magnet commercially available, neodymium magnets have revolutionized modern technology, powering everything from electric motors and wind turbines to headphones, medical devices, and magnetic separators. The exceptional strength of neodymium magnets results from the alignment of their atomic dipoles under a magnetic field, a phenomenon quantified in their magnetic hysteresis loop. Even after the external field is removed, a significant portion of this atomic alignment is retained within the neodymium magnet, making these magnets highly efficient for a wide range of applications.

Understanding the grades of neodymium magnets is vital for users who need to evaluate magnetic performance for specific industrial or consumer applications. Grades signify the maximum energy product of a magnet and are expressed in mega gauss oersteds (MGOe), which is a direct indicator of the peak values in the BH Curve—a critical factor in determining the strength and efficiency of neodymium magnets. Higher grades represent stronger magnets with greater magnetic field intensity and greater resistance to demagnetization.

The widely used "N" grading scale encompasses ratings from N30 to N52, and in advanced applications such as aerospace and advanced electronics, N55 magnets have become available, boasting a 6% increase in magnetic strength over N52. Letter suffixes such as SH (Super High), UH (Ultra High), and EH (Extra High) denote enhanced properties, specifically the coercivity (Hc) of the neodymium magnet, which measures its ability to maintain magnetization at elevated temperatures. Selecting the right grade and temperature performance is essential—higher coercivity ensures neodymium magnets resist demagnetization in high-temperature environments.

Previously, N52 stood at the pinnacle of neodymium magnet strength, but the development of N55 neodymium magnets, now regarded as the strongest rare earth magnets available, has further expanded possibilities for compact yet powerful designs. Industries such as renewable energy, electronics, and automotive manufacturing increasingly rely on premium grades like N52 and N55 when optimal magnetic flux and limited space are critical factors.

The chart below provides details on the most commonly used grades of neodymium magnets today to help users compare magnetic properties and select the best magnet for specific industrial or commercial applications.

Most Common Grades of Neodymium Magnets

Nxx	NxxM	NxxH	NxxSH	NxxUH	NxxEH
N30	N30M	N30H	N30SH	N28UH	N28EH
N33	N33M	N33H	N33SH	N30UH	N30EH
N35	N35M	N35H	N35SH	N33UH	N33EH
N38	N38M	N38H	N38SH	N35UH	N35EH
N40	N40M	N40H	N40SH	N38UH	N38EH
N42	N42M	N42H	N42SH	N40UH	N33VH
N45	N45M	N45H	N45SH		N33AH
N48	N48M	N48H
N50	N50M
N52

The approximate maximum working temperature for each neodymium magnet grade is provided below. Select the grade that matches your performance needs, as exceeding recommended temperature ratings can diminish magnetic strength or lead to irreversible demagnetization. The "XX" represents the maximum energy product in MGOe, a key factor when evaluating neodymium magnets for use in motors, sensors, medical equipment, and other advanced applications.

Maximum Working Temperature of Each Neodymium Magnet Grade

Neodymium Grade	Max Temp
Nxx 12000 Oe	80 C/175 F
NxxM 14000 Oe	100 C/212 F
NxxH 17000 Oe	120 C/248 F
NxxSH 20000 Oe	150 C/302 F
NxxUH 25000 Oe	180 C/356 F
NxxEH 30000 Oe	200 C/392 F
NxxVH 35000 Oe	230 C/446 F
NxxAH 35000 Oe	230 C/446 F

The Properties of Neodymium Magnets

Remanence

Remanence, or residual magnetism, is a critical property of neodymium magnets (NdFeB magnets) and greatly influences their utility in various applications. When neodymium is exposed to a strong magnetic field, its atomic dipoles become aligned. Even after this external field is removed, a substantial portion of the alignment endures, resulting in powerful, long-lasting magnetization. Technically, remanence refers to the residual magnetic flux density—measured in teslas (T)—that remains when the external field decreases from saturation to zero. High remanence means increased magnetic flux density, an essential parameter in magnetic assemblies, electric motors, and magnetic coupling devices.

The remanence of neodymium magnets varies according to their manufacturing process. Sintered neodymium magnets, made using powder metallurgical techniques, typically exhibit remanence values from 1.0 to 1.4 T, making them some of the most powerful permanent magnets available. By comparison, bonded neodymium magnets offer a more flexible form factor but have lower remanence, usually around 0.6 to 0.7 T. This makes sintered neodymium the preferred choice for high-strength, compact magnet applications.

Coercivity

Coercivity, the measure of a magnet's resistance to demagnetization, plays a vital role in the performance and durability of neodymium magnets. After magnetization, these rare earth magnets retain their magnetic field even in the absence of an external magnetic influence. However, when subjected to an opposing magnetic field or elevated temperatures, a certain threshold, known as the coercive force (Hc), needs to be exceeded to demagnetize the magnet.

Coercivity in neodymium magnets is typically quantified in oersteds (Oe) or ampere turns per meter (A/m). Sintered neodymium magnets offer exceptional coercivity, with a range of 750 Oe to 2000 Oe, while bonded neodymium magnets fall within 600 Oe to 1200 Oe. Enhanced grades like SH, UH, and EH are engineered for environments where strong resistance to demagnetization and elevated working temperatures are required, commonly found in sectors such as aerospace or automotive engineering.

Energy Product

The magnetic energy product, commonly referred to as (BH)_max, is a primary metric for evaluating the power of neodymium magnets. It represents the maximum product of magnetic flux density (B) and magnetic field strength (H), expressed in units such as Mega Gauss Oersteds (MGOe). Higher (BH)_max values equate to stronger magnetic fields and higher efficiency in magnetic circuits, making neodymium magnets the preferred solution for high-performance motor applications, advanced magnetic assemblies, and miniaturized components where space-saving is essential.

Magnetic flux density (B) is measured in teslas (SI) or gauss (CGS), with common applications utilizing magnets with values up to 6000 Gauss. For precise measurement in engineering and manufacturing environments, a gaussmeter or teslameter is used. The linear demagnetization curve of neodymium magnets ensures predictable, stable performance over the magnet’s lifecycle.

Permanent magnets like neodymium types maintain their B field both within the magnet and in the surrounding area, which can be crucial for magnetic sensing, separation, or actuation. For intricate magnetic designs, advanced simulation software aids in calculating precise flux densities and magnetic field distributions based on magnet geometry, orientation, and material properties.

When selecting a neodymium magnet for your project, it’s important to compare energy products and flux density needs against application demands, factoring in size constraints, environmental conditions, and essential safety considerations.

Curie Temperature

The Curie temperature, or Curie point, indicates the critical temperature at which a neodymium magnet loses its ferromagnetic properties and becomes paramagnetic. At temperatures approaching 320°C (608°F), the molecular alignment that causes magnetism rapidly disperses, causing the magnet to lose its effective magnetic field. Understanding the Curie temperature is particularly important when selecting magnets for high-temperature environments, including electric vehicle drive trains, wind turbines, and other heavy-duty applications subjected to thermal stress.

In neodymium magnets, increased temperatures can initially cause an increase in coercivity, but as the Curie temperature nears, a sharp decrease in both magnetic strength and coercivity occurs. Prolonged exposure to temperatures beginning at 80°C (176°F) can result in a gradual and eventually irreversible loss of magnetic properties, so careful grade selection and proper thermal management are vital for optimal performance and longevity.

Magnet experts often recommend using high-coercivity neodymium grades (e.g., SH, UH, EH) for environments where elevated temperatures are expected, ensuring that magnetic assemblies for critical industrial, automotive, and electronic systems remain stable over their intended lifespan.

How to Choose the Right Neodymium Magnet for Your Application

Choosing the ideal neodymium magnet involves considering multiple performance factors:

• Required magnetic strength and grade for your application (N35 to N55)
• Operating and maximum exposure temperatures
• Coercivity demands for demagnetization resistance
• Physical size, shape, and available mounting options
• Corrosion resistance, especially for humid or challenging environments
• Compliance with safety standards and regulatory requirements

For specific requirements, consulting with a trusted neodymium magnet manufacturer or supplier can help ensure the perfect match for your project, enabling you to achieve optimal performance, durability, and cost-effectiveness while minimizing risk of failure. Whether you need strong holding force, miniaturization, or specialized thermal characteristics, today’s high-performance neodymium magnets offer a solution for virtually every high-tech application.

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Chapter Three – How are Neodymium Magnets Made?

Neodymium magnets are produced through two primary methods: sintering and bonding. The final characteristics of the magnets depend on the manufacturing process used, with sintering generally providing superior properties compared to bonding.

How Neodymium Magnets are Made

Sintering

Melting

To create neodymium magnets, Neodymium, Iron, and Boron are carefully measured and placed in a vacuum induction furnace to form an alloy. Additional elements like cobalt, copper, gadolinium, and dysprosium may be included to enhance specific properties such as corrosion resistance. The alloy is heated using electrical eddy currents in a vacuum environment to prevent contamination. The composition of the neodymium alloy can vary depending on the manufacturer and the grade of the magnet.

Powdering

The molten metal is solidified into blocks, which are then processed through jet milling in a nitrogen and argon environment to produce a fine micron-sized powder. This neodymium powder is subsequently loaded into a hopper for compression.

Pressing

The powder is compacted into a mold that is slightly oversized compared to the final shape using a technique called upsetting, conducted at approximately 725°C. The extra size of the mold accommodates for material contraction during the sintering phase. During this compaction process, the material is subjected to a magnetic field and then placed into a secondary mold to be shaped further, ensuring that the magnetization aligns with the pressing direction. Some techniques involve using fixtures that generate magnetic fields during pressing to better orient the particles.

Prior to removing the pressed magnet, it is exposed to a demagnetizing pulse to ensure it remains in a demagnetized state, resulting in a "green" magnet that is fragile and exhibits suboptimal magnetic characteristics.

Sintering

Sintering, also known as frittage, consolidates and shapes the green magnet by applying heat below its melting point, thus imparting the final magnetic characteristics. This process is conducted under strict control in an inert, oxygen-free environment to prevent oxidation, which could impair the magnet's performance. The material is heated up to 1080°C, just shy of its melting point, to encourage the particles to bond together.

A rapid cooling process, or quenching, is then employed to quickly lower the temperature of the magnet. This helps to minimize the formation of phases that could degrade the alloy's magnetic properties.

Machining

After sintering, the magnets are shaped to precise specifications using diamond or wire cutting tools for grinding.

Plating and coating

Neodymium is highly susceptible to oxidation and corrosion, which can impair its magnetic properties. To safeguard against this, the magnets are coated with materials such as plastic, nickel, copper, zinc, or tin.

Magnetization

Even though the magnet has a specific direction of magnetization, it remains unmagnetized until it is briefly subjected to a powerful magnetic field generated by a wire coil surrounding it. This magnetization process utilizes capacitors and high voltage to create a strong current.

Final Inspection

Digital measuring projectors are used to check the dimensions, while x-ray fluorescence technology is employed to verify the thickness of the coating. Additional tests are performed to assess the coating's quality and durability. The BH curve is analyzed using a hysteresis graph to ensure that the magnet achieves full magnetization.

Bonding

Bonding, also known as compression bonding, involves pressing a blend of neodymium powder and an epoxy binder. This mixture consists of 97% magnetic material and 3% epoxy.

The blend is either compressed in a press or extruded and then cured in an oven. This method allows for the creation of magnets in intricate shapes and configurations due to the pressing or extrusion process. Compression bonding results in magnets with precise tolerances and eliminates the need for further processing.

Compression bonded magnets are isotropic and can be magnetized in any direction, which includes multi-polar configurations. The epoxy binding makes the magnets strong enough to be milled or lathed but not be drilled or tapped.

Radial Sintered

Radially oriented neodymium magnets represent the latest advancement in magnet technology. Although the technique for creating radially aligned magnets has been known for years, it was previously not cost-effective. Recent technological advancements have optimized the production process, making these magnets more accessible to manufacture.

There are three primary methods for producing radially aligned neodymium magnets: anisotropic pressure molding, hot pressing with backward extrusion, and radial rotating field alignment.

The sintering process plays a crucial role in ensuring the magnet's structure is free from weak points.

A distinctive feature of radially oriented magnets is their magnetic field direction, which extends around the magnet's perimeter. In this arrangement, the south pole is located on the inner side of the ring, while the north pole is positioned on the outer edge.

Radially oriented neodymium magnets exhibit anisotropic properties, with magnetization extending from the center of the ring outward. This radial magnetization enhances the magnet's strength and allows for various configurations.

These radially aligned neodymium ring magnets find applications in synchronous motors, stepping motors, and DC brushless motors across industries such as automotive, computing, electronics, and communications.

Chapter Four - What are the applications for neodymium magnets?

Since their introduction in the early 1980s, neodymium magnets have become the most prevalent type among various magnets. They are utilized in numerous everyday items, including disk drives and magnetic components in cars and airplanes. Neodymium magnets can be manufactured in a range of sizes while maintaining their original magnetic strength.

Applications of Neodymium Magnets

Magnetic Separation Conveyors

In the demonstration shown below, the conveyor belt is equipped with neodymium magnets arranged with alternating poles facing outward. This configuration provides a strong magnetic grip. Objects that are not magnetic will fall off, while ferromagnetic materials are attracted and collected in a bin.

Hard disk drives

Hard drives contain tracks and sectors filled with magnetic cells. These cells are magnetized to store data when information is written to the drive.

Water Treatment

Neodymium magnets are employed in water treatment systems to help mitigate scaling caused by hard water, which contains high levels of calcium and magnesium. In magnetic water treatment, water flows through a magnetic field that aims to capture and reduce scale buildup. While this technology has not yet been universally accepted as fully effective, there have been some promising results.

Reed Switches

A reed switch is an electrical switch operated by a magnetic field. They have two contacts and metal reeds in a glass envelope. The contacts of the switch are open until activated by a magnet.

Reed switches are employed in various mechanical systems as proximity sensors, such as in doors and windows for burglar alarms and tamper-proofing. In laptops, reed switches trigger sleep mode when the lid is closed. Additionally, pedal keyboards for pipe organs utilize reed switches enclosed in glass to shield the contacts from dirt, dust, and debris.

Sewing Magnets

Neodymium sew-in magnets are commonly used for magnetic clasps on purses, clothing, and folders or binders. These sewing magnets are sold in pairs, with one magnet being positive (+) and the other negative (–).

Denture Magnets

Magnets embedded in a patient's jaw can help secure dentures in place. To protect the magnets from corrosion caused by saliva, they are coated with stainless steel plating. Additionally, a layer of ceramic titanium nitride is applied to prevent abrasion and minimize exposure to nickel.

Magnetic Doorstops

Magnetic doorstops are mechanical devices designed to keep a door open. When the door swings open and makes contact with the magnet, it remains in place until it is manually pulled away from the magnet.

Jewelry Clasp

Magnetic jewelry clasps consist of two halves sold as a pair. Each half features a magnet encased in a non-magnetic housing. A metal loop on each half allows attachment to the chain of a bracelet or necklace. The housings are designed to interlock, which prevents side-to-side or shearing movement between the magnets, ensuring a secure connection.

Speakers

Speakers transform electrical energy into mechanical energy or motion. This motion compresses air and converts it into sound energy or sound pressure levels. An electric current passing through a wire coil generates a magnetic field within a permanent magnet attached to the speaker. The voice coil interacts with this magnetic field, causing the cone to move back and forth. This movement creates pressure waves in the air, which we perceive as sound.

Anti-Lock Brake Sensors

In anti-lock braking systems, neodymium magnets are embedded within copper coils in the brake sensors. The system manages wheel acceleration and deceleration by adjusting the brake line pressure. Control signals, generated by the system's controller and sent to the brake pressure modulating unit, are derived from wheel speed sensors.

As the sensor ring's teeth pass by the magnetic sensor, they cause changes in the magnetic field's polarity, generating a frequency signal that corresponds to the axle's angular velocity. This signal is then used to determine the wheels' acceleration.

Chapter Five – What should you consider when using neodymium magnets?

Neodymium magnets, being among the most powerful and strongest magnets available, can pose significant risks if not handled properly. It is crucial to manage these magnets with care to avoid potential harm. Below are descriptions of some of the negative effects associated with neodymium magnets.

Negative Effects of Neodymium Magnets

Bodily Injury

Neodymium magnets are capable of snapping together with great force, potentially pinching skin or causing serious injuries. They can attract from several inches to even feet apart, and if a finger is caught between them, it can result in severe harm or fractures. Due to their immense strength, the force between neodymium magnets can be unexpectedly intense compared to other types of magnets.

Magnet Breakage

Neodymium magnets are brittle and can easily peel, chip, crack, or shatter if they collide with force, potentially sending sharp metal fragments flying at high speeds. Although they are made from metal and have a shiny appearance, their hardness makes them quite fragile. It is important to wear eye protection when handling neodymium magnets to prevent injury from these flying fragments.

Keep Away from Children

Neodymium magnets are not toys and should not be handled by children. Small magnets pose a choking hazard, and if multiple magnets are swallowed, they can attract to each other through the intestinal walls, leading to severe health problems that necessitate immediate emergency surgery.

Danger to Pacemakers

A magnetic field strength of ten gauss can affect pacemakers or defibrillators, as neodymium magnets generate powerful magnetic fields. These fields can interfere with pacemakers, implantable cardioverter-defibrillators (ICDs), and other implanted medical devices, potentially causing them to deactivate when exposed to magnetic fields.

Magnetic Media

The intense magnetic fields produced by neodymium magnets can damage magnetic media, including floppy disks, credit cards, magnetic ID cards, cassette tapes, and video tapes. They can also adversely affect older electronic devices such as televisions, VCRs, computer monitors, and CRT displays. Therefore, neodymium magnets should be kept away from electronic appliances to avoid potential damage.

GPS and Smartphones

Magnetic fields can disrupt the operation of compasses, magnetometers, and the internal compasses found in smartphones and GPS devices. The International Air Transport Association (IATA) and U.S. federal regulations govern the shipping of magnets to ensure safe handling and transportation.

Nickel Allergy

If you have a nickel allergy, your immune system treats nickel as a harmful substance and produces chemicals to combat it, leading to symptoms such as redness and skin rashes. Nickel allergies are more prevalent in women and girls, with about 36 percent of women under 18 affected. To prevent an allergic reaction, it is best to avoid neodymium magnets that are coated with nickel.

Demagnetization

Neodymium magnets maintain their effectiveness up to 80°C (175°F). However, the temperature at which they start to lose their magnetic properties can vary depending on the grade, shape, and specific application of the magnets.

Flammable

Neodymium magnets should not be drilled or machined, as the dust and powder generated during grinding are flammable.

Corrosion

Neodymium magnets are coated or plated to protect them from environmental damage. However, they are not waterproof and can rust or corrode if exposed to wet or moist conditions.

Chapter Six – What are the standards and regulations for using neodymium magnets?

Despite their powerful magnetic fields, neodymium magnets are very brittle and require careful handling. Various industrial monitoring agencies have established regulations for their handling, manufacture, and shipping. Below is a brief overview of some of these regulations.

Standards and Regulations for Neodymium Magnets

American Society of Mechanical Engineers

The American Society of Mechanical Engineers (ASME) sets standards for Below-The-Hook Lifting Devices. ASME Standard B30.20 covers the installation, inspection, testing, maintenance, and operation of lifting devices, including lifting magnets where the operator positions and guides the load. ASME Standard BTH-1 is applied in conjunction with ASME B30.20 to provide additional guidelines.

Hazard Analysis and Critical Control Points

Hazard Analysis and Critical Control Points (HACCP) is an internationally recognized preventive risk management system focused on food safety. It addresses biological, chemical, and physical hazards by requiring the identification and control of risks at specific points in the production process. HACCP also provides certification for equipment used in food facilities, including separation magnets that have been specifically identified and certified for use in the food industry.

United States Department of Agriculture

Magnetic separation equipment has been approved by the United States Department of Agriculture Agricultural Marketing Service as being in compliance for use with two food processing programs:

• Dairy Equipment Review Program
• Meat and Poultry Equipment Review Program

Certification is based on the following two standards or guidelines:

• Sanitary Design and Fabrication of Dairy Processing Equipment
• Sanitary Design and Fabrication of Meat and Poultry Processing Equipment which meet NSF/ANSI/3-A SSI 14159-1-2014 Hygiene Requirements

Restriction of Use of Hazardous Substances

The Restriction of Hazardous Substances (RoHS) regulations restrict the use of lead, cadmium, polybrominated biphenyl (PBB), mercury, hexavalent chromium, and polybrominated diphenyl ether (PBDE) flame retardants in electronic equipment. Because neodymium magnets can pose hazards, RoHS has established standards for their handling and use.

International Civil Aviation Organization

Magnets are classified as dangerous goods for shipments outside the Continental United States to international destinations. For air transport, any packaged material must have a magnetic field strength of 0.002 Gauss or more at a distance of seven feet from any point on the surface of the package.

Federal Aviation Administration

Packages containing magnets shipped by air must be tested to ensure they meet established standards. The magnetic field strength must be less than 0.00525 Gauss at a distance of 15 feet from the package. For powerful magnets, appropriate shielding is required. Due to potential safety hazards, there are numerous regulations and requirements governing the air shipment of magnets.

Restriction, Evaluation, Authorization of Chemicals

The Restriction, Evaluation, and Authorization of Chemicals (REACH) is an international regulation within the European Union that sets standards for hazardous materials. It provides guidelines and documentation for the proper use, handling, and manufacture of magnets, with a focus on their application in medical devices and electronic components.

Conclusion

• Neodymium (Nd-Fe-B) magnets, known as neo magnets, are common rare earth magnets composed of neodymium (Nd), iron (Fe), boron (B), and transition metals.
• The two processes used to manufacture neodymium magnets are sintering and bonding.
• Neodymium magnets have become the most widely used of the many varieties of magnets.
• The magnetic field of a neodymium magnet occurs when a magnetic field is applied to it and the atomic dipoles align, which is the magnetic hysteresis loop.
• Neodymium magnets can be produced in any size but retain their initial magnetic strength.

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