Samarium - cobalt (Sm-Co) magnets

Samarium-cobalt magnets (Sm-Co) classified to the group of modern magnets of the type called rare-earth element-metal (Re-M), the first mass-produced magnets.

They are manufactured using a method of powder metallurgy, as a rule, anisotropic magnets. At present, such magnets are manufactured on the basis of two intermetallic compounds SmCo5 (plastics S18, S20), or Sm2Co17 (plastics S22, S24, S26, S28, S30), whereas Sm2Co17 type of magnets are characterised by bigger values of remanence Br and slightly better temperature stability.

SmCo magnets

The values of energy density (BH)max of Sm-Co magnets are over five times bigger than those of ferrite or alnico magnets, whereas those of coercive force jHc are over twice bigger towards ferrite magnets. Their susceptibility to oxidation that vehemently increases over 250 °C makes that their maximum working temperature Tmax is much lower than that of Curie point Tc. This is the main reason restricting the range of application of such magnets.

Among the qualities of samarium-cobalt magnets one can mention, first of all, high temperature stability of magnetic parameters (similar to that of alnico magnets), considerable values of energy density (BH)max, coercive force jHc, as well as remanence Br.

One ought also to take notice of very high corrosion resistance of SmCo magnets in the scope of allowable working temperatures, which owing to high values of coercive force jHc can be used in strong demagnetizing fields.

Samarium-cobalt magnets are installed in small motors and generators, measuring instruments and check apparates, various types of converters and sensors, as well as many other devices that require stable magnetic field in variable temperatures (-60 - 250 °C). Application of Sm-Co magnets having high values of both of magnetic energy density and coercive force enables miniaturization of the devices that so far were manufactured using ferrite and alnico magnets.


Magnetic properties typical for samarium-cobalt magnets:

Symbol of
material

Remanecence
(Br)

Coercive
force
(bHc)

Coercive
force
(jHc)

Energy
density
(BH)max

[T]

[kGs]

[kA/m]

[kOe]

[kA/m]

[kOe]

[kJ/m3]

[MGsOe]

S16

0,81-0,85 8,1-8,5 620-660 7,8-8,3 1194-1830 15-23 110-127

14-16

S18

0,85-0,90 8,5-9,0 660-700 8,3-8,8 1194-1830 15-23 127-143

16-18

S20

0,90-0,94 9,0-9,4 680-725 8,5-9,1 1194-1830 15-23 150-167

19-21

S22

0,92-0,96 9,2-9,6 710-750 8,9-9,4 1194-1830 15-23 160-175

20-22

S24

0,96-1,0 9,6-10,0 730-770 9,2-9,7 1194-1830 15-23 175-190

22-24

S24GH

0,95-1,02 9,5-10,2 700-750 8,7-9,4 min.1990 min.25 175-191

22-24

S26GH

1,02-1,05 10,2-10,5 750-780 9,4-9,8 min.1990 min.25 191-207

24-26

S28GH

1,03-1,08 10,3-10,8 756-796 9,5-10,0 min. 1990 min. 25 207-220

26-28

S30GH

1,08-1,1 10,8-11,0 788-835 9,9-10,5 min. 1990 min. 25 220-240

28-30

S24G*

0,95-1,02 9,5-10,2 700-750 8,7-9,4 min. 1443 min. 18 175-191

22-24

S26G*

1,02-1,05 10,2-10,5 750-780 9,4-9,8 min. 1443 min. 18 191-207

24-26

S28G*

1,03-1,08 10,3-10,8 756-796 9,5-10,0 min. 1443 min. 18 207-220

26-28

S30G*

1,08-1,1 10,8-11,0 788-835 9,9-10,5 min. 1443 min. 18 220-240

28-30

S26M

1,02-1,05 10,2-10,5 750-780 9,4-9,8 955-1273 12-16 191-207

24-26

S28M

1,03-1,08 10,3-10,8 756-796 9,5-10,0 955-1273 12-16 207-220

26-28

S30M

1,08-1,1 10,8-11,0 788-835 9,9-10,5 955-1273 12-16 220-240

28-30

S28L

1,02-1,08 10,2-10,8 413-716 5,2-9,0 438-796 5,5-10,0 207-220

26-28

S30L*

1,08-1,15 10,8-11,5 413-716 5,2-9,0 438-796 5,5-10,0 220-240

28-30

*) Former S24, S26, S28 and S30

Other physical properties typical for samarium-cobalt magnets:

Symbol of
material

Coefficient of
remanecence
temperature
TK (Br)

Coefficient of
coercive
temperature
TK (jHc)

Density

Vickers
hardness

Resistivity

Curie
Temp.

Max.
working
temp.

[%/oC]

[%/oC]

[g/cm3]

[Hv]

[Ohm cm]

[oC]

[oC]

S16, S18, S20, S22, S24

-0,05

-0,3

8,0-8,2

450-500

5-6 x 10-5

700-750

250

S24GH, S26GH, S28GH

-0,03

-0,2

8,3-8,5

550-600

8-9 x 10-5

min. 800

350

S24G, S26G, S28G, S30G

-0,03

-0,2

8,3-8,5

550-600

8-9 x 10-5

min. 800

300

S26M, S28M, S30M

-0,03

-0,2

8,3-8,5

550-600

8-9 x 10-5

min. 800

300

S28L, S30L

-0,03

-0,2

8,3-8,5

540-600

8-9 x 10-5

min.800

250