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rare earth permanent magnets, sintered neodymium iron boron, NdFeB magnetsSintered NdFeB magnets, i.e. sintered neodymium iron boron magnets, are those permanent magnetic materials that based on a Nd-Fe-B tetragonal crystal structure, and they are manufactured through a powder metallurgy (PM) process. They contain three basic elements neodymium, iron and boron. The neodymium element can be substituted by a portion of other rare earth elements (REEs) including praseodymium (Pr), dysprosium (Dy), terbium (Tb), cerium (Ce), etc. The iron element can be substituted by a portion of cobalt (Co) element to increase the magnets’ Curie temperature (Tc), thermal stability and corrosion resistance. In order to control the microstructure and the microchemistry so as to meet required performance, it also adds a small portion of other metal elements including aluminium (Al), copper (Cu), niobium (Nb), gallium (Ga), etc.

Almost at the same time in the early 1980s, NdFeB magnets were invented by M. Sagawa’s and J. J. Croat’s teams through a powder metallurgical process and a melt-spinning technique, respectively. Due to their outstanding magnetic properties (high remanence Br: 1.1-1.5 T, middle high coercivity Hcj: 800-3000 kA/m3 and high maximum energy product (BH)max: 220-430 kJ/m3) together with competitive cost, sintered NdFeB magnets are widely applied in direct current (DC) motors, servo motors, stepper/stepping motors, synchronous motors, linear motors, voice coil motors (VCMs), wind turbines and generators, magnetic resonance imaging (MRI), electric power steering (EPS), magnetic separation, etc.

>> Sintered NdFeB Magnets’ Grades and Their Magnetic Properties

Grade Br Hcb Hcj (BH)max Tw
kGs T kOe kA/m kOe kA/m MGOe kJ/m3 ºC
N52 14.2-14.8 1.42-1.48 ≥10.5 ≥836 ≥11 ≥876 50-53 398-422 ≤80
N50 13.9-14.4 1.39-1.44 ≥10.8 ≥859 ≥12 ≥955 48-51 382-406
N48 13.6-14.1 1.36-1.41 ≥11.6 ≥923 46-49 366-390
N45 13.2-13.7 1.32-1.37 ≥11.6 ≥923 43-46 342-366
N42 12.8-13.3 1.28-1.33 ≥11.4 ≥907 40-43 318-342
N40 12.4-12.9 1.24-1.29 ≥11.4 ≥907 38-41 302-326
N38 12.1-12.6 1.21-1.26 ≥11.2 ≥891 36-39 286-310
N35 11.7-12.2 1.17-1.22 ≥10.8 ≥859 33-36 263-286
N33 11.3-11.8 1.13-1.18 ≥10.5 ≥836 31-34 247-271
N30 10.8-11.3 1.08-1.13 ≥10.0 ≥796 28-31 223-247
N50M 13.9-14.4 1.39-1.44 ≥13.0 ≥1035 ≥13 ≥1035 48-51 382-406 ≤100
N48M 13.6-14.1 1.36-1.41 ≥12.8 ≥1019 ≥14 ≥1114 46-49 366-390
N45M 13.2-13.7 1.32-1.37 ≥12.5 ≥995 43-46 342-366
N42M 12.8-13.3 1.28-1.33 ≥12.0 ≥955 40-43 318-342
N40M 12.4-12.9 1.24-1.29 ≥11.6 ≥923 38-41 302-326
N38M 12.1-12.6 1.21-1.26 ≥11.3 ≥899 36-39 286-310
N35M 11.7-12.2 1.17-1.22 ≥10.9 ≥867 33-36 263-286
N33M 11.3-11.8 1.13-1.18 ≥10.5 ≥836 31-34 247-271
N30M 10.8-11.3 1.08-1.13 ≥10.0 ≥796 28-31 223-247
N50H 13.9-14.4 1.39-1.44 ≥13.0 ≥1035 ≥16 ≥1273 48-51 382-406 ≤120
N48H 13.6-14.1 1.36-1.41 ≥12.8 ≥1019 ≥17 ≥1353 46-49 366-390
N45H 13.2-13.7 1.32-1.37 ≥12.5 ≥995 43-46 342-366
N42H 12.8-13.3 1.28-1.33 ≥12.0 ≥955 40-43 318-342
N40H 12.4-12.9 1.24-1.29 ≥11.6 ≥923 38-41 302-326
N38H 12.1-12.6 1.21-1.26 ≥11.3 ≥899 36-39 286-310
N35H 11.7-12.2 1.17-1.22 ≥10.9 ≥867 33-36 263-286
N33H 11.3-11.8 1.13-1.18 ≥10.5 ≥836 31-34 247-271
N30H 10.8-11.3 1.08-1.13 ≥10.0 ≥796 28-31 223-247
N48SH 13.6-14.1 1.36-1.41 ≥12.8 ≥1019 ≥20 ≥1592 46-49 366-390 ≤150
N45SH 13.2-13.7 1.32-1.37 ≥12.5 ≥995 43-46 342-366
N42SH 12.8-13.3 1.28-1.33 ≥12.0 ≥955 40-43 318-342
N40SH 12.4-12.9 1.24-1.29 ≥11.6 ≥923 38-41 302-326
N38SH 12.1-12.6 1.21-1.26 ≥11.3 ≥899 36-39 286-310
N35SH 11.7-12.2 1.17-1.22 ≥10.9 ≥867 33-36 263-286
N33SH 11.3-11.8 1.13-1.18 ≥10.5 ≥836 31-34 247-271
N30SH 10.8-11.3 1.08-1.13 ≥10.0 ≥796 28-31 223-247
N42UH 12.8-13.3 1.28-1.33 ≥12.2 ≥971 ≥25 ≥1990 40-43 318-342 ≤180
N40UH 12.4-12.9 1.24-1.29 ≥11.8 ≥939 38-41 302-326
N38UH 12.1-12.6 1.21-1.26 ≥11.5 ≥915 36-39 286-310
N35UH 11.7-12.2 1.17-1.22 ≥11.1 ≥883 33-36 263-286
N33UH 11.3-11.8 1.13-1.18 ≥10.7 ≥851 31-34 247-271
N30UH 10.8-11.3 1.08-1.13 ≥10.2 ≥812 28-31 223-247
N40EH 12.4-12.9 1.24-1.29 ≥11.8 ≥939 ≥30 ≥2388 38-41 302-326 ≤200
N38EH 12.1-12.6 1.21-1.26 ≥11.5 ≥915 36-39 286-310
N35EH 11.7-12.2 1.17-1.22 ≥11.1 ≥883 33-36 263-286
N33EH 11.3-11.8 1.13-1.18 ≥10.7 ≥851 31-34 247-271
N30EH 10.8-11.3 1.08-1.13 ≥10.2 ≥812 28-31 223-247
N35AH 11.7-12.2 1.17-1.22 ≥11.1 ≥883 ≥35 ≥2786 33-36 263-286 ≤230
N33AH 11.3-11.8 1.13-1.18 ≥10.7 ≥851 31-34 247-271
N30AH 10.8-11.3 1.08-1.13 ≥10.2 ≥812 28-31 223-247
N28AH 10.4-10.9 1.04-1.09 ≥9.8 ≥780 26-29 207-231
Note:
∗ The data in the above table were samples’ results tested at the temperature of 20 °C.
∗ The temperature coefficients of Br and Hcj are α(Br): -0.09~-0.12 %/ºC and β(Hcj): -0.40~-0.60 %/ºC, respectively.
∗ The above data are only for reference, magnets can be tailored according to customers’ personalized requirements.

>> Sintered NdFeB Magnets’ Shapes, Magnetization Direction and Size Range

Shape Graphic Description Magnetization Direction Size Range
Disc/Cylinder disc neodymium magnets size range Disc/Cylinder neodymium magnets Axially Magnetized Axially Magnetized D: 1-100 mm
T: 0.3-100 mm
Disc/Cylinder neodymium magnets Diametrically Magnetized Diametrically Magnetized D: 1-100 mm
T: 0.3-100 mm
Ring ring neodymium magnets size range ring neodymium magnets Axially Magnetized Axially Magnetized OD: 1.5-100 mm
ID: 0.5-90 mm
T: 0.5-60 mm
ring neodymium magnets Diametrically Magnetized Diametrically Magnetized OD: 1.5-100 mm
ID: 0.5-90 mm
T: 0.5-60 mm
ring neodymium magnets Radially Magnetized Radially Magnetized OD: 20-200 mm
ID: 10-180 mm
T: 0.5-60 mm
Block/Rectangular block neodymium magnets size range block neodymium magnets Thickness Magnetized Thickness Magnetized L: 1-160 mm
W: 0.5-100 mm
T: 0.3-100 mm
Arc/Segment arc/segment neodymium magnets size range arc/segment_neodymium_magnets_Diametrically_magnetization Diametrically Magnetized OD-ID≥1 mm
L: 1-160 mm
W: 3-100 mm
H: 1-80 mm
arc/segment neodymium magnets Radially Magnetized Radially Magnetized OD-ID≥1 mm
L: 1-80 mm
W: 3-40 mm
H: 1-10 mm
Note:
∗ Other shapes of sintered NdFeB magnets can also be tailored according to customers’ specific requirements.

>> Sintered NdFeB Magnets’ Coating Types

Coating Thickness (μm) SST (hr) PCT (hr) Tw (ºC)
Zn (Zinc) 5-15 >24 - ≤160
C-Zn (Colored Zinc) 5-15 >48 - ≤160
Electroless Nickel 10-30 >96 >72 ≤230
NiCuNi (Nickel Copper Nickel) 10-20 >48 >48 ≤230
NiCu + Black Nickel 10-20 >48 >72 ≤230
NiCuNi + Tin 10-25 >48 >48 ≤160
NiCuNi + Gold 10-25 >48 >48 ≤230
NiCuNi + Silver 10-25 >48 >48 ≤160
Epoxy 10-30 >72 >48 ≤160
Teflon 10-20 >96 - ≤230
Everlube 10-20 >96 >72 ≤230
Parylene 0.2-5 >96 - ≤230
Note:
∗ Salt spray test (SST) was conducted at 35 ºC with 5% NaCl solution.
∗ Pressure cooker test (PCT) was conducted at 120 ºC, 2 atm and 100% RH.

>> Some Physical Properties of Sintered NdFeB Magnets

Parameter Unit Value
Density (ρ) g/cm3 7.4-7.7
Curie Temperature (Tc) ºC 310-370
Recoil Permeability (μrec) - 1.05
Vickers Hardness (HV) MPa 500-600
Bending Strength (σbb) MPa 200-400
Compressive Strenght (σbc) MPa 1000-1100
Tensile Strength (σb) MPa 80-90
Resistivity (ρ) μΩ·m 1.4-1.6
Thermal Conductivity (λ) W/(m·K) 8-10
Young's Modulus (E) GPa 150-200
Thermal Expansivity ∥ Magnetization (α) 10-6/ºC 3-4
Thermal Expansivity ⊥ Magnetization (α) 10-6/ºC 1-3
Note:
∗ The above data are only for reference, specific magnets maybe have different values.