Ferrite magnets

From among all types of magnets, ferrite magnets are most often manufactured in the world. They are made from barium ferrite (BaFe12O19), or strontium ferrite (SrFe12O19), as isotropic or anisotropic materials. The manufacturing methods of those magnets are similar to production processes of other ceramic materials. When manufacturing anisotropic magnets, pressing is carried out within the magnetic field that orients grains according to the axes of easy magnetization, along the lines of field forces. When manufacturing isotropic ferrite magnets, no outside magnetic field is applied in the course of pressing. That is why anisotropic magnets reach much higher values of the basic magnetic parameters (about four times bigger energy density (BH)max, and about twice higher remanence Br).

Ferrite magnets

The values of remanence Br of ferrite magnets are about 2,3 times smaller than those of other types of magnets (Nd-Fe-B, Sm-Co and Alnico magnets), and therefore to obtain high density magnetic flux applied are magnets of big cross-sections and of circuits that concentrate magnetic field. The values of energy density (BH)max of ferrite magnets approximate those of Alnico magnets. However, ferrite magnets have repeatedly higher (about. 3,8 times) values of coercive force jHc, which enables their application in relatively strong demagnetizing fields. Moreover, although the temperature stability of magnetic parameters is poor (low), their maximum working temperature Tmax is high (lower only when compared with alnico magnets). However, be careful when applying them in low temperatures, for their coercive force jHc gets quickly reduced when the temperature drops. In many applications a ferrite magnet constitutes an advantageous compromise between economic and technical requirements.

Magnetic properties typical for ferrite magnets:

Symbol of
material

 

Remanence
(Br)

Coercive force
(bHc)

Coercive force
(jHc)

Energy
density
(BH)max

[mT]

[kGs]

[kA/m]

[kOe]

[kA/m]

[kOe ]

[kJ/m3]  

[MGsOe] 

F10T
(izotrope)

200-235

2,00-2,35

125-160

1,57-2,01

210-280

2,64-3,52

6,5-9,5 

0,82-1,19

F20

320-380

3,20-3,80

135-190

1,70-2,39

140-195

1,76-2,45

18,0-22,0

2,26-2,76

F25

360-400

3,60-4,00

135-170

1,70-2,14

140-200

1,76-2,51

22,5-28,0

2,83-3,52

F30

370-400

3,70-4,00

175-210

2,20-2,64

180-220

2,26-2,77

26,0-30,0

3,27-3,77

F30BH

380-400

3,80-4,00

230-275

2,89-3,46

235-290

2,95-3,65

27,0-32,5

3,39-4,08

F35

410-430

4,10-4,30

220-250

2,77-3,14

225-255

2,83-3,21

31,5-35,0

3,96-4,40


Other physical properties typical for ferrite magnets:

Temperature
coefficient of
remanence TK (Br)
Temperature
coefficient of
coercive force TK (jHc)
Density
(d)
Resistivity
(r)
Curie
point
(Tc)

[%/oC]

[%/oC]

[g/cm3]

[Ohm cm]

[oC]

-0,19

0,40

4,0 - 5,1

104 - 108

450