Neodymium Magnet

A neodymium magnet (also known as NdFeB, NIB or Neo magnet) is the most widely used type of rare-earth magnet. It is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd₂Fe₁₄B tetragonal crystalline structure. Developed independently in 1984 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet available commercially. Because of different manufacturing processes, they are divided into two subcategories, namely sintered NdFeB magnets and bonded NdFeB magnets. They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as electric motors in cordless tools, hard disk drives and magnetic fasteners. Our company mainly focused on manufacturing sintered neodymium magnet.

History

General Motors (GM) and Sumitomo Special Metals independently discovered the Nd₂Fe₁₄B compound almost simultaneously in 1984. The research was initially driven by the high raw materials cost of SmCo permanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd₂Fe₁₄B magnets, while Sumitomo developed full-density sintered Nd₂Fe₁₄B magnets. GM commercialized its inventions of isotropic Neo powder, bonded neo magnets, and the related production processes by founding Magnequench in 1986 (Magnequench has since become part of Neo Materials Technology, Inc., which later merged into Molycorp). The company supplied melt-spun Nd₂Fe₁₄B powder to bonded magnet manufacturers. The Sumitomo facility became part of the Hitachi Corporation, and has manufactured but also licensed other companies to produce sintered Nd₂Fe₁₄B magnets.

Current Status and Trends

Based on the control of much of the world’s rare-earth mines, China is currently the world’s largest producer of rare earth permanent magnets. In recent years, its output has basically remained above 90% of the global total. In the past ten years, the global output of rare earth NdFeB has increased from 120,000 tons to the current annual output of 250,000 tons. In the next five years, as the demand for new energy vehicles, wind power and electronic products continues to grow, the output of rare earth permanent magnets may increase to 500,000 tons. Relying on the advantages of China’s magnetic material industry and our company’s continuous research and development over the years, our magnet production process has been continuously optimized. Some new products such as Radially Oriented Ring Magnets will gradually open up new market prospects in the future.

Properties

(See more parameters)

Grade

Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets. For sintered NdFeB magnets, there is a widely recognized international classification. Their values range from 28 up to 52. The first letter N before the values is short for neodymium, meaning sintered NdFeB magnets. Letters following the values indicate intrinsic coercivity and maximum operating temperatures (positively correlated with the Curie temperature), which range from default (up to 80 °C or 176 °F) to AH (230 °C or 446 °F).

Magnetic properties

Some important properties used to compare permanent magnets are:

Remanence (Br), which measures the strength of the magnetic field.
Coercivity (Hcj), the material’s resistance to becoming demagnetized.
Maximum energy (BHmax), the density of magnetic energy, characterized by the maximum value of magnetic flux density(B) times magnetic field strength (H).
Curie temperature (TC), the temperature at which the material loses its magnetism.

Temperature effects

Neodymium has a negative coefficient, meaning the coercivity along with the magnetic energy density (BHmax) decreases with temperature. Neodymium-iron-boron magnets have high coercivity at room temperature, but as the temperature rises above 100 °C (212 °F), the coercivity decreases drastically until the Curie temperature (around 320 °C or 608 °F). This fall in coercivity limits the efficiency of the magnet under high-temperature conditions such as in wind turbines, hybrid motors, etc. Dysprosium (Dy) or terbium (Tb) is added to curb the fall in performance from temperature changes, making the magnet even more expensive.

Production

Sintered Nd-magnets are prepared by the raw materials being melted in a furnace, cast into a mold and cooled to form ingots. The ingots are pulverized and milled; the powder is then sintered into dense blocks. The blocks are then heat-treated, cut to shape, surface treated and magnetized. (See more process)

Machinery Process

Neodymium material is brittle and prone to chipping and cracking, so it does not machine well by conventional methods. Machining the magnets will generate heat, which if not carefully controlled, can demagnetize the magnet. Many shapes that would be easy to manufacture in a steel or aluminum part are not necessarily feasible in a neodymium magnet. Complex shapes or shapes with thin cross sections might not be possible. The neodymium magnet shape should fit within the boundaries of a 220 x 220 x 80mm box, with the magnetization direction in the 80mm direction.

(See more available dimensions)

Surface Treatment

Sintered Nd₂Fe₁₄B tends to be vulnerable to corrosion, especially along grain boundaries of a sintered magnet. This type of corrosion can cause serious deterioration, including crumbling of a magnet into a powder of small magnetic particles, or spalling of a surface layer. This vulnerability is addressed in many commercial products by adding a protective coating to prevent exposure to the atmosphere. Nickel plating or two-layered copper-nickel plating are the standard methods, although plating with other metals, or polymer and lacquer protective coatings, are also in use.

(See more coating types)

Magnetization

Neodymium magnets are formed with a preferred magnetization direction. They are pressed in the presence of a magnetic field that orients the magnetic domains in one direction. The magnets are actually magnetized later in the process, long after they are formed. Once a magnet is made, it can only be magnetized in that “preferred” direction.
Magnets can be supplied in the magnetized or non-magnetized state. For the delivery of magnetized parts we have various packaging methods available.

(See more magnetization types)

Applications

Neodymium magnets have replaced alnico and ferrite magnets in many of the myriad applications in modern technology where strong permanent magnets are required, because their greater strength allows the use of smaller, lighter magnets for a given application.

Some examples are: Servomotors Lifting and compressor motors Synchronous motors Spindle and stepper motors Electrical power steering Drive motors for hybrid and electric vehicles Electric generators for wind turbines Hard Disk Drives Automotive Engineering and Sensors NMR-Analysis Equipment and MRI-Tomographs Electroacoustics Magnetic Couplings Magnetic Separation Permanent Magnet Bearings Holding Systems Switches and Relays Measuring Instruments

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