Overview of Neodymium Magnets

Neodymium magnets belong to the category of permanent magnets, crafted using an alloy of Neodymium (Nd), Iron (Fe), and Boron (B), forming the Nd2Fe14B crystalline structure. Frequently referred to as “Neo magnets” or “NdFeB magnets,” these terms serve as shorthand for “Neodymium” and “Neodymium Iron Boron,” respectively, highlighting their composition. Neodymium magnets are also commonly recognized as rare earth magnets, reflecting the rare earth materials in their composition.

Based on production methods, Neodymium magnets are classified into sintered, bonded, and hot-pressed types, each offering distinct characteristics for specific industrial needs. Among these, the term “Neodymium magnets” is most commonly associated with sintered magnets, which dominate the global market due to their unmatched magnetic strength and efficiency. Neodymium magnets remain the strongest permanent magnets available, widely utilized across various industries for their superior performance and versatility.

Neodymium Magnets-Main

How Are Neodymium Magnets Made?

The production of Neodymium magnets starts with creating an alloy through vacuum melting followed by the strip-casting (SC) technique. The resulting alloy strips are initially broken into coarse particles using a hydrogen decrepitation process. These particles are then finely ground into a powder with particle sizes between 3 and 7 microns using a jet-milling process.

Next, the fine powder is placed into molds and subjected to pressing while a magnetic field aligns the particles. The resulting compacted material, known as the green body, is sintered in a vacuum furnace at approximately 1100°C to achieve solidification. Following sintering, the magnets are machined into their final shapes, surface-treated for durability, and magnetized to activate their magnetic properties.

Preloader
  • Weighing

    Weighing

  • Melting and Strip Casting

    Melting and Strip Casting

  • Hydrogen Decrepitation

    Hydrogen Decrepitation

  • Jet Milling

    Jet Milling

  • Pressing

    Pressing

  • Sintering

    Sintering

  • Machining

    Machining

  • Surface Treatment

    Surface Treatment

  • Magnetization

    Magnetization

  • Packaging and Shipping

    Packaging and Shipping

Magnetic Properties of Neodymium Magnets

Neodymium magnets are categorized using a grading system that typically includes the letter “N” followed by a number and sometimes additional letters. The “N” stands for Neodymium, while the number represents the magnet’s maximum energy product (BH)max, measured in Mega-Gauss Oersted (MGOe).

Suffix letters indicate the magnet’s intrinsic coercivity and maximum operating temperature. For instance, grades with “M” (Medium), “H” (High), “SH” (Super High), “UH” (Ultra High), “EH” (Extreme High), or “AH” (Abnormal High) require minimum intrinsic coercivity values of 14, 17, 20, 25, 30, and 35 kOe, respectively. Corresponding maximum operating temperatures are 100°C, 120°C, 150°C, 180°C, 200°C, and 220°C.

Notably, some grades lack a suffix, such as the widely recognized N35 and N52. These grades have an intrinsic coercivity of at least 12 kOe and a maximum operating temperature below 80°C. Additionally, grain boundary diffused Neodymium magnets are distinguished by a “G” prefix, highlighting their unique manufacturing process.

Grade of Neodymium Magnets-updated
Magnetic Properties Chart of Neodymium Magnets
Grade Remanence

Br

 Coercivity

Hcb

 Intrinsic Coercivity

Hcj

 Max. Energy Product

(BH)max

 Max. Working Temperature
T kGs kA/m kOe kA/m kOe kJ/m3 MGOe ℃
N35 1.17-1.22 11.7-12.2 ≥868 ≥10.9 ≥955 ≥12 263-287 33-36 80
N38 1.22-1.25 12.2-12.5 ≥899 ≥11.3 ≥955 ≥12 287-310 36-39 80
N40 1.25-1.28 12.5-12.8 ≥923 ≥11.6 ≥955 ≥12 302-326 38-41 80
N42 1.28-1.32 12.8-13.2 ≥923 ≥11.6 ≥955 ≥12 318-342 40-43 80
N45 1.32-1.37 13.2-13.7 ≥876 ≥11.0 ≥955 ≥12 342-366 43-46 80
N48 1.37-1.42 13.7-14.2 ≥892 ≥11.2 ≥955 ≥12 366-390 46-49 80
N50 1.39-1.44 13.9-14.4 ≥836 ≥10.5 ≥955 ≥12 374-406 47-51 80
N52 1.42-1.47 14.2-14.7 ≥836 ≥10.5 ≥876 ≥11 390-422 49-53 80
N55 1.46-1.52 14.6-15.2 ≥716 ≥9.0 ≥876 ≥11 414-446 52-56 60
N30M 1.08-1.13 10.8-11.3 ≥796 ≥10.0 ≥1114 ≥14 223-247 28-31 100
N33M 1.13-1.17 11.3-11.7 ≥836 ≥10.5 ≥1114 ≥14 247-271 31-34 100
N35M 1.17-1.22 11.7-12.2 ≥868 ≥10.9 ≥1114 ≥14 263-287 33-36 100
N38M 1.22-1.25 12.2-12.5 ≥899 ≥11.3 ≥1114 ≥14 287-310 36-39 100
N40M 1.25-1.28 12.5-12.8 ≥923 ≥11.6 ≥1114 ≥14 302-326 38-41 100
N42M 1.28-1.32 12.8-13.2 ≥955 ≥12.0 ≥1114 ≥14 318-342 40-43 100
N45M 1.32-1.37 13.2-13.7 ≥995 ≥12.5 ≥1114 ≥14 342-366 43-46 100
N48M 1.37-1.43 13.7-14.3 ≥1019 ≥12.8 ≥1114 ≥14 358-390 45-49 100
N50M 1.40-1.45 14.0-14.5 ≥1035 ≥13.0 ≥1114 ≥14 374-406 47-51 100
N52M 1.43-1.48 14.3-14.8 ≥1050 ≥13.2 ≥1114 ≥14 398-422 50-53 100
N35H 1.17-1.22 11.7-12.2 ≥868 ≥10.9 ≥1353 ≥17 263-287 33-36 120
N38H 1.22-1.25 12.2-12.5 ≥899 ≥11.3 ≥1353 ≥17 287-310 36-39 120
N40H 1.25-1.28 12.5-12.8 ≥923 ≥11.6 ≥1353 ≥17 302-326 38-41 120
N42H 1.28-1.32 12.8-13.2 ≥955 ≥12.0 ≥1353 ≥17 318-342 40-43 120
N45H 1.32-1.36 13.2-13.6 ≥971 ≥12.2 ≥1353 ≥17 342-366 43-46 120
N48H 1.36-1.42 13.6-14.2 ≥1027 ≥12.9 ≥1353 ≥17 358-390 45-49 120
N50H 1.40-1.45 14.0-14.5 ≥1035 ≥13.0 ≥1353 ≥17 374-406 47-51 120
N33SH 1.13-1.17 11.3-11.7 ≥844 ≥10.6 ≥1592 ≥20 247-271 31-34 150
N35SH 1.17-1.22 11.7-12.2 ≥876 ≥11.0 ≥1592 ≥20 263-287 33-36 150
N38SH 1.22-1.25 12.2-12.5 ≥907 ≥11.4 ≥1592 ≥20 287-310 36-39 150
N40SH 1.25-1.28 12.5-12.8 ≥939 ≥11.8 ≥1592 ≥20 302-326 38-41 150
N42SH 1.28-1.32 12.8-13.2 ≥971 ≥12.2 ≥1592 ≥20 318-342 40-43 150
N45SH 1.32-1.37 13.2-13.7 ≥979 ≥12.3 ≥1592 ≥20 342-366 43-46 150
N48SH 1.36-1.42 13.6-14.2 ≥995 ≥12.5 ≥1592 ≥20 358-390 45-49 150
N33UH 1.13-1.17 11.3-11.7 ≥852 ≥10.7 ≥1990 ≥25 247-271 31-34 180
N35UH 1.17-1.22 11.7-12.2 ≥860 ≥10.8 ≥1990 ≥25 263-287 33-36 180
N38UH 1.22-1.25 12.2-12.5 ≥876 ≥11.0 ≥1990 ≥25 287-310 36-39 180
N40UH 1.25-1.28 12.5-12.8 ≥915 ≥11.5 ≥1990 ≥25 302-326 38-41 180
N42UH 1.28-1.32 12.8-13.2 ≥971 ≥12.2 ≥1990 ≥25 318-342 40-43 180
N30EH 1.08-1.13 10.8-11.3 ≥812 ≥10.2 ≥2388 ≥30 223-247 28-31 200
N33EH 1.13-1.17 11.3-11.7 ≥820 ≥10.3 ≥2388 ≥30 247-271 31-34 200
N35EH 1.17-1.22 11.7-12.2 ≥836 ≥10.5 ≥2388 ≥30 263-287 33-36 200
N38EH 1.22-1.25 12.2-12.5 ≥915 ≥11.5 ≥2388 ≥30 287-310 36-39 200
N28AH 1.02-1.09 10.2-10.9 ≥780 ≥9.8 ≥2786 ≥35 199-231 25-29 230
N30AH 1.08-1.13 10.8-11.3 ≥812 ≥10.2 ≥2786 ≥35 215-247 27-31 230
N33AH 1.13-1.17 11.3-11.7 ≥852 ≥10.7 ≥2786 ≥35 247-271 31-34 230
  • The above-mentioned data of magnetic properties are given at room temperature.
  • The max working temperature of magnet is changeable due to length-diameter ratio, coating thickness and other environment factors.
Additional Magnetic Properties of Neodymium Magnets
Parameters Unit Reference Range
Temperature Coefficient of Br / α(Br) %/℃ -0.08 ~ -0.13
Temperature Coefficient of Hcj/ β(Hcj) %/℃ -0.35 ~ -0.80
Curie Temperature / Tc ℃ 310-380
Recoil Permeability / μrec – 1.05

Physical Properties of Neodymium Magnets

Beyond their magnetic and chemical characteristics, the long-term operational stability of Neodymium magnets is heavily influenced by their physical properties, including mechanical, electrical, and thermal attributes.

Mechanical properties are assessed through compressive strength, tensile strength, and bending strength. These factors significantly impact both the machinability of Neodymium magnets and their durability in long-term applications.

Electrical properties are evaluated by measuring electrical resistivity. Neodymium magnets exhibit relatively low resistivity, making them susceptible to eddy current losses when used in rotating machinery.

Thermal properties are commonly defined by the coefficient of thermal expansion. The dimensional changes caused by thermal expansion can induce stresses between the magnet and its assembly materials due to mismatched expansion rates. These stresses may lead to mechanical damage and a decline in magnetic performance over time.

Physical Properties Chart of Neodymium Magnets
Items Parameters Unit Reference Range
Regular Physical Properties Density / ρ g/cm3 7.40-7.80
Electrical Properties Electrical Resistivity / ρ μΩ·m 1.4
Mechanical Properties Vickness Hardness / HV – 550-650
Compressive Strength MPa 1050
Tensile Strength / σ MPa 80
Bending Strength / σ MPa 290
Thermal Properties Thermal Conductivity / k W/(m·K) 6-8
Coefficient of Thermal Expansion / α 10-6/K C⊥: -1.5, C∥: 6.5.

Surface Treatment of Neodymium Magnets

Surface treatment is an essential step in ensuring the durability and corrosion resistance of Neodymium magnets. These magnets feature a multi-phase microstructure primarily composed of the Nd2Fe14B main phase, along with Nd-rich and B-rich phases. The Nd-rich phase is highly prone to oxidation and forms a galvanic couple with Nd2Fe14B grains in humid conditions, accelerating corrosion. While adding substitutional elements can improve stability, it often compromises magnetic performance. To address this, a protective barrier layer is applied to shield the magnets from corrosion.

Surface treatment methods for Neodymium magnets are categorized into wet and dry processes:

  • Wet Processes: These involve treating the magnet surfaces using pure water, inorganic, or organic solutions. Common techniques include phosphating, electroplating, electroless plating, spray coating, and dip coating.
  • Dry Processes: These methods involve physical or chemical treatments without direct immersion in solutions. Typical examples are physical vapor deposition (PVD) and chemical vapor deposition (CVD).

These processes provide essential protection, enhancing the longevity and reliability of Neodymium magnets in various applications.

Classification of Surface Treatments for Neodymium Magnets
Coating Thickness

(μm)

 Color SST

(hrs)

 PCT

(hrs)

 Characteristics
BW-Zn 5-8 Bright blue ≥24 – Suitable protection for most products.
Color-Zn 5-8 Shining color ≥48 – Suitable protection for most products.
Ni-Cu-Ni 10-30 Bright silver 24-72 24-72 Excellent resistance to salt spray and humidity, ideal for clean environments.
Black Ni 10-30 Dark silver 48-72 48-72 Resistance to salt spray.
Ni-Cu-Ni-Au/Ag 10-30 Golden/Silver 24-72 24-72 Offers excellent decorative performance.
Ni-Cu-Ni-Sn 10-30 Silver ≥72 ≥48 Resistance to salt spray.
Ni-Cu-Ni-Cr 10-30 Silver ≥48 ≥48 Resistance to salt spray and abrasion.
Phosphate 1-3 Dark grey – – Temporary protection.
Epoxy resin 10-30 Black/Grey ≥96 ≥48 Resistance to salt spray.
Ni-Cu-Epoxy resin 10-30 Black/Grey ≥96 ≥48 Resistance to salt spray.
Parylene – – ≥24 ≥24 Excellent humidity, salt spray, corrosive vapors, and solvents resistance. Free of pore.
Everlube 5-10 Golden/Black ≥96 ≥120 Excellent resistance to salt spray and humidity.
Teflon – Black 48-72 48-72 Resistance to salt spray and abrasion.
Note: corrosion resistance is also influenced by the magnet’s geometry and dimensions.

Magnetization Directions of Neodymium Magnets

Permanent magnets, including Neodymium magnets, must undergo a magnetization process before being used in specific applications. This process involves applying an external magnetic field in a specified direction until the magnet reaches magnetic saturation. Due to their high coercivity, Neodymium magnets require a stronger external magnetic field compared to other magnets, making fast impulse magnetization the preferred method.

An impulse magnetization system consists of two primary components: the magnetizer and the magnetizing fixture. The magnetizer is a device that stores electrical energy in a capacitor, which is then rapidly discharged into the magnetizing fixture. The magnetizing fixture, also called a magnetizing coil or yoke, generates the required magnetic field strength and ensures proper magnetization patterns or directions.

As anisotropic magnets, Neodymium magnets have a preferred direction of magnetization, allowing for the creation of various pole configurations, provided they align with the magnet’s orientation direction.