Hard Ferrite Magnets

Also known as ceramic magnets, they are mainly Strontium based (SrFe2O3), manufactured with strontium carbonate additives. The process consists in milling the raw materials compound hexaferrite into single crystals approximating a single domain in size.

Then the powder is wet or dry pressed in a die under the influence of a magnetic field. Their good coercive force results from high crystal anisotropy of Strontium iron oxide. However, isotropic parts can also be produced where a simple and easy multi-pole magnetization is required. Nowadays, Ferrite is the cheapest available magnetic material. The most common shapes are simple, such as blocks, cylinders, rings and arcs. The dimensional tolerances from the mould are quite wide and it must be ground, usually on the magnetization axis, to obtain tight mechanical tolerances. Very hard and brittle, Ferrite is not conductive and has high resistance against corrosion, acids, salts, lubricants and gases.

Ferrite
quality category

Remanence
(Br)

Coercivity force(HcB)

Coercivity force(HcJ)

Energy product
(BHmax)

Max. operating temperature

 

mT

KGs

kA/m

KOe

kA/m

KOe

kJ/m³

MGOe

°C

HF 10


200-220

2.0-2.2

125-145

1.57-1.82

210-250

2.64-3.14

6.5-8

0.8-1.0

250

HF 25


360-370

3.6-3.7

135-150

1.70-1.88

140-170

1.76-2.14

22.5-25.3

2.8-3.2

250

HF 30


380-385

3.8-3.85

190-210

2.40-2.64

200-220

2.50-2.77

26-28

3.4-3.7

250

HF 33


410-420

4.1-4.2

220-235

2.77-2.95

225-240

2.83-3.01

31,5-33

4.0-4.2

250

HF 35


400-410

4.0-4.1

175-190

2.20-2.45

180-200

2.26-2.51

30-32

3.8-4.0

250

HF 30BH


380-390

3.8-3.9

223-235

2.80-2.95

230-245

2.90-3.08

27-30

3.4-3.8

250

The specific density of isotropic hard ferrites (HF10) is at 4,5-4,7 g/cm³, while the density of anisotropic hard ferrites is at 4,8-4,9 g/cm³


Temperature coefficient of remanence Br: -0,2 %/°C (for 20 °C to 100 °C)


Temperature coefficient of coercivity (HcJ): 0,3 %/°C (for 20 °C to 100 °C)


Curie temperature: 450 °C

 

A complete overview of the available magnet systems can be found in our Technical Data Sheet for hard ferrite magnets.