Neodymium magnet, also known as NdFeB magnet, is a tetragonal crystal system formed by neodymium, iron and boron (Nd2Fe14B).
In 1982, Masato Sagawa of Sumitomo Special Metals discovered neodymium magnets. The magnetic energy product (BHmax) of this magnet is greater than the samarium cobalt magnet, which is the largest magnetic energy product in the world at that time. Later, Sumitomo Special Metals successfully developed powder metallurgy process, and General Motors successfully developed melt-spinning process, which can prepare Ndfeb magnets. This magnet is today’s magnetic second only to the absolute zero holmium magnet permanent magnet, is also the most commonly used rare earth magnet. Ndfeb magnets are widely used in electronic products, such as hard drives, mobile phones, headphones and battery-powered tools.
Classifications of NdFeb Magnets
Magnets can be divided into “permanent magnets” and “non-permanent magnets”. Permanent magnets can be natural, also known as natural magnets, or they can be manufactured artificially. Non-permanent magnets, such as electromagnets, only exhibit magnetism under certain conditions.
NdFeB permanent magnets are divided into sintered NdFeB and bonded NdFeB. Bonded NdFeB has magnetic properties in all directions and is corrosion resistant. Sintered NdFeB, on the other hand, is prone to corrosion and requires coating on the surface, typically zinc plating, nickel plating, environmentally friendly zinc, environmentally friendly nickel, nickel-copper-nickel, environmentally friendly nickel-copper-nickel, etc. Sintered NdFeB magnets are generally magnetized axially or radially, depending on the required working surface.
In order to avoid corrosion damage, it is necessary to do protection treatment on the surface of permanent magnet materials, such as electroplating with gold, nickel, zinc, tin, and spraying epoxy resin on the surface.
Product Description
Each type of product is divided into several brands according to the maximum magnetic energy product size.
NdFeB magnetic material grades include: N35—N52, 35M—50M, 30H—48H, 30SH—45SH, 28UH—35UH, 28EH—35EH.
Grade example: 048021 means sintered NdFeB permanent magnet material with (BH) max of 366~398kj/m3 and Hcj of 800KA/m.
The brand name of sintered NdFeB permanent magnet material consists of three parts: the main name and two magnetic properties. The first part is the main name, which consists of the chemical symbol ND of the neodymium element, the chemical symbol FE of the iron element and the chemical symbol B of the boron element. The second part is the number before the line, which is the nominal value of the material’s maximum magnetic energy product (BH) max (unit: kj/m3). The third part is the number after the slash, the magnetic polarization intensity coercive force value (unit: One-tenth of KA/m), the value is rounded off.
Grade example: NdFeb380/800 means sintered NdFeB permanent magnet material with (BH) max of 366~398kj/m3 and Hcj of 800KA/MR.
NdFeB surface treatment:
- Phosphating;
- Inorganic salt passivation;
- Electroplating;
- Electrophoresis;
- Vacuum deposition;
There are three main performance parameters to determine the performance of a magnet:
- Remanence (Br): Remanence is the magnetic induction remaining in a magnetized material after the removal of an applied magnetic field. It is the magnetic flux density retained by the magnet when it is magnetized to saturation and then the external magnetic field is removed.
- Coercivity (Hc): Coercivity is the intensity of the reverse magnetic field that must be applied to a magnetized material to reduce the induction flux density (B) to zero after it has been magnetized to saturation.
- Energy product (BH): Energy product represents the magnetic energy density established in the gap space (between the two poles of the magnet), i.e., the static magnetic energy per unit volume of the gap. Since this energy is equal to the product of the magnetic induction (Bm) and the magnetic field intensity (Hm), it is called the energy product.
In addition, we have:
- Magnetic field: The space where a magnetic force is exerted by a magnet’s poles.
- Surface magnetic field: The magnetic induction strength at a specified position on the surface of a magnet.
Regarding magnetic properties:
- Diamagnetism: Diamagnetism is a property of some materials that causes them to create a weak repulsive force in response to an applied magnetic field.
- Paramagnetism: Paramagnetism refers to the magnetic state of some materials that can be influenced by an external magnetic field, causing them to exhibit a magnetization vector in the same direction as the external field. Such materials have positive magnetic susceptibility. The opposite phenomenon to paramagnetism is called diamagnetism.
- Ferromagnetism: Ferromagnetism refers to the magnetic state of some materials that exhibit spontaneous magnetization. Iron is the most well-known material with ferromagnetic properties. Some materials, when magnetized by an external magnetic field, can maintain their magnetization even after the external field is removed, which is known as spontaneous magnetization. All permanent magnets exhibit ferromagnetism or ferrimagnetism.
Magnet Applications
Sintered NdFeB permanent magnet materials have excellent magnetic properties and are widely used in electronics, electric machinery, medical equipment, toys, packaging, hardware machinery, aerospace and other fields. The more common ones include permanent magnet motors, speakers, magnetic separators, Computer disk drives, magnetic resonance imaging equipment instruments, etc.
Curie temperature
The Curie temperature is the point at which a magnet loses its permanent magnetism:
- NdFeB: 320°C–460°C.
- Ferrite: 260°C–465°C.
- Samarium Cobalt: 700°C–800°C.
Summary
Neodymium magnets are highly versatile, with unmatched strength and a broad range of applications, from electronics to aerospace. Their continued evolution ensures they remain integral in modern technology.
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