Neodymium sintered magnets (Nd-Fe-B), NdFeB Magnet

From among the group of modern magnets of rare earth-metal (Re-M) type, neodymium sintered magnets (Nd-Fe-B) achieved the biggest market success. They owe their excellent magnetic properties to Nd2Fe14B compound, discovered in 1984. The very magnets are manufactured using methods of powder metallurgy, and thanks to pressing in a magnetic field, or plastic working in elevated temperature, they get anisotropic structure. Maximum energy density (BH)max (ca. 400 kJ/m3) of the magnets is very high. They also have high values of remanence induction Br, similar to those of alnico magnets; fields of their coercive force jHc are repeated dozens of times higher, which make possible to install them under strong demagnetizing fields. Compared with samarium-cobalt magnets they show a smaller range of working temperatures, and their magnetic properties depend, in a considerably greater measure, on temperature. Due to the contents of neodymium that shows big susceptibility to oxidation, the magnets are coated with thin anticorrosive layers. Ni, Zn, Ni-Zn lub Ni-Cu-Ni are the most often applied layers. It is also possible to coat the magnets with plate, gold, gold-nickel layers, apply phosphate coating or epoxidation.

The most important qualities of sintered neodymium magnet are: extremely high values of energy density (BH)max, very high values of coercive force jHc, and big values of remanence Br. Thanks to the above, they can be installed in the products for which miniaturization is required. Neodymium sintered magnets (Nd-Fe-B) are installed, above all, in motors, generators, electronic equipment (loudspeakers, microphones, alarms, and so on), mechanical toys, separators, servo-motors, holders (grips) and many other devices, where strong magnetic field is required, however in a range of not very high temperatures.

Magnetic properties typical for neodymium sintered magnets:

Symbol of
material

Remanence
(Br)

Coercive
force

(bHc)

Coercive
force

jHc)

Energy density
(BH) max.

Max.
working
temp. *

[NdFeB]

[kGs]

[kOe]

 [kOe]

[kJ/m3]

[MGsOe]

[oC]

N27 10,2-11,0 min. 9,6 min. 12,0 199-223

25-28

80

N30 10,8-11,5 min. 10,0 min. 12,0 223-247 28-31 80
N33 11,3-11,7 min. 10,5 min. 12,0 247-263 31-33 80
N35 11,7-12,1 min. 10,8 min. 12,0 263-286 33-36 80
N38 12,1-12,5 min. 11,3 min. 12,0 287-310 36-38 80
N40 12,5-12,8 min. 11,6 min. 12,0 302-326 38-41 80
N42 12,8-13,2 min. 11,6 min. 12,0 318-342 40-43 80
N45 13,2-13,8 min. 11,0 min. 12,0 342-366 43-46 80
N48 13,7-14,2 min. 10,5 min. 11,0 366-390 46-49 80
N50 14,0-14,5 min. 10,5 min. 11,0 366-390 47-51 80
N52 14,3-14,8 min. 10,5 min. 11,0 380-412 49-53 80
N27M 10,2-11,0 min. 9,6 min. 14,0 199-223 25-28 100
N30M 10,8-11,5 Min. 10,0 Min. 14,0 223-247 28-31 100
N33M 11,3-11,7 min. 10,5 min. 14,0 247-263 31-33 100
N35M 11,7-12,1 min. 10,9 min. 14,0 263-286 33-36 100
N38M 12,1-12,5 min. 11,3 min. 14,0 287-310 36-38 100
N40M 12,5-12,8 min. 11,6 min. 14,0 302-326 38-42 100
N42M 12,8-13,2 min. 12,0 min. 14,0 318-342 40-44 100
N45M 13,2-13,8 min. 12,5 min. 14,0 334-366 42-46 100
N48M 13,7-14,2 min. 12,8 min. 14,0 358-390 46-49 100
N50M 14,0-14,5 min. 13,1 min. 14,0 374-406 47-51 100
N27H 10,2-11,0 min. 9,6 min. 17,0 199-223 25-28 120
N30H 10,8-11,3 min. 10,2 min. 17,0 220-247 30-31 120
N33H 11,3-11,7 min. 10,5 min. 17,0 247-263 31-33 120
N35H 11,7-12,1 min. 10,9 min. 17,0 263-287 33-36 120
N38H 12,1-12,5 min. 11,3 min. 17,0 287-310 36-38 120
N40H 12,5-12,8 min. 11,6 min. 17,0 302-326 38-41 120
N42H 12,8-13,2 min. 12,0 min. 17,0 318-342 40-43 120
N44H 13,0-13,7 min. 12,1 min. 17,0 326-358 41-45 120
N45H 13,2-13,6 min. 12,5 min. 17,0 342-374 43-47 120
N46H 13,2-13,8 min. 12,3 min. 17,0 342-374 43-47 120
N48H 13,7-14,3 min. 12,5 min. 17,0 366-390 46-49 120
N27SH 10,2-11,0 min. 9,6 min. 20,0 199-223 25-28 150
N30SH 10,8-11,3 Min. 10,2 Min. 20,0 220-247 30-31 150
N33SH 11,3-11,7 Min. 10,6 Min. 20,0  247-271

31-34

150

N35SH 11,6-12,1 min. 10,8 min. 20,0 247-263 31-33 150
N38SH 12,1-12,5 min. 11,4 min. 20,0 287-310 36-38 150
N40SH 12,5-12,8 min. 11,8 min. 20,0 302-326 38-41 150
N42SH 12,9-13,7 min. 12,0 min. 20,0 326-358 41-45 150
N45SH 13,3-13,5 min. 12,2 min. 20,0 345-360 44-46 150
N28UH 10,2-10,8 min. 9,6 min. 25,0 207-231 26-29 180
N30UH 10,8-11,3 min. 10,2 min. 25,0 223-247 28-31 180
N33UH 11,3-11,9 min. 10,7 min. 25,0 247-263 31-34 180
N35UH 11,7-12,3 min. 11,0 min. 25,0 263-295 33-37 180
N38UH 12,1-12,9 min. 11,6 min. 25,0 287-318 36-40 180
N40UH 12,5-13,2 min. 10,5 min. 25,0 289-334 38-42 180
N28EH 10,4-10,9 min. 9,8 min. 30,0 207-231 26-29 200
N30EH 10,9-11,7 min. 10,2 min. 30,0 223-255 28-32 200
N33EH 11,4-12,2 min. 10,7 min. 30,0 247-279 31-35 200
N35EH 11,8-12,5 min. 10,5 min. 30,0 263-295 33-37 200

*) Maximum working temperature depends on height/diameter ratio of the magnet, and also on the type of magnetic circuit in which the magnet is placed.

Other physical properties typical for neodymium sintered magnets:

Coefficient temp. of remanecence
TK (Br)

Coefficient temp. of coercive force TK (jHc)

Density
(d)

Vickers hardness 
(HV)

Resistivity(r)

Curie
Point(Tc)

[%/oC]

[%/oC]

[g/cm3]

[kG/mm2]

Ohm cm]

[oC]

- 0,10... - 0,12

- 0,6

7,4 - 7,6   

600

144

310 -340