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2.6.6 Magnetic properties of materials

Many magnetic properties of materials are expressed in terms of the magnetic field strength H, magnetic flux density B and the magnetic polarization J. The SI units of H and B are, respectively, ampere per metre (A m−1) and tesla (T).

The relation between the quantities expressed in SI units is:

              B= μ0 H + J

in which µ0 is 4π × 10−7 H m−1, the magnetic constant (permeability of free space). The absolute permeability, μ( = B/H) and the volume susceptibility κ (= J/μ0H), are thus related by the equation:

            μ = μ0(1 + κ)

The mass susceptibility χ is equal to κ/ρ, where ρ is the density. The relative permeability μr = μ/μ0 is the permeability of the material relative to that of a vacuum and is the value given in the tables.

In ferromagnetic materials as H is increased steadily from zero the permeability changes and is at first relatively small, its value being defined as the initial permeability, then reaches a maximum value, and finally decreases towards μ0 as the polarization tends towards a limiting value (Bμ0H). The flux density remaining when H is reduced to zero is the remanent flux density and the negative H needed to reduce B to zero is the coercive force. The remanent flux density and coercive force for a cycle which proceeds to saturation are called the remanence, Br, and the coercivity, HcB. In an open magnetic circuit the variation of J with H is usually measured and the coercivity is then denoted by HcJ.

When a ferromagnetic material is taken through a cycle of magnetization there is a loss of energy as heat due to the combined effects of hysteresis, induced eddy currents and domain wall motion. The hysteresis loss per unit volume, Qh = H dB, has been shown empirically to vary as B1.6max over a limited range of peak flux density of up to about 1 T for high saturation materials, and 0.5 T for low saturation materials. This relationship, known as the Steinmetz law, is nevertheless only approximate. Some indication of the second loss, namely the eddy current power loss, may be calculated from standard formulae once certain relevant physical parameters are known. In their present forms, however, these formulae are only approximate. The total power losses that will be dissipated in laminar material when an alternating flux is developed in it has a direct bearing on the efficiency that can be realized in equipment such as transformers and electric motors and should therefore be known accurately. Accordingly the power losses of representative forms of typical materials are measured and some of these are given in Table (3) in terms of power loss per unit mass.

Many magnetic properties of ferromagnetic materials depend greatly on previous history, state of strain, temperature, size, perfection and orientation of crystals, and the effect of small traces of impurity may be enormous.

When heated, ferromagnetic materials become paramagnetic at a temperature known as the (ferromagnetic) Curie point.

Ferrimagnetic materials (ferrites) have all of the above characteristics of ferromagnetic materials. However, due to their high resistivity, soft (low coercivity) ferrites are widely used in high frequency applications, in which case the following parameters are also of interest:


(a) 

Power loss density—this is another name for specific total power loss, but for ferrite materials the loss is usually expressed per unit volume.

(b)  

Loss factor—the performance of ferrites at low field strengths is often indicated by the expression tan δ where δ is the loss angle, i.e. the phase angle between B and H. However, information regarding power losses is usually given in the form of loss factors normalized to unit permeability, μ, since this facilitates the calculation of loss coefficients of gapped ferrite cores. Hence the loss factor is:

         tan δ   =  tan δh   + tan δe   + tan δr
         μ μ μ μ

where tan δh, tan δe and tan δr are the loss angles for the hysteresis, eddy current and residual losses respectively, all of which are present to a greater or lesser extent and combine to give the total loss, tan δ.

(c)

IEC hysteresis coefficient ηB—in considering recommendations for standard forms of loss expression, the International Electrotechnical Commission agreed the following relationship for the hysteresis coefficient, ηB,

       ηB tan δh
μBmax

(d)

Temperature factor—the permeability of a magnetic material may change for a variety of reasons, the most obvious being the change of temperature. Over a limited temperature range the relationship between the reversible change in magnetic permeability, Δμ, and the corresponding change in temperature, Δθ, is given by the temperature coefficient, TC:


   

TC

Δμ

μΔθ

As with the loss factor, it is usual to normalize the values to unit permeability which gives the loss factor:


    loss factor =  Δμ

·

μ2Δθ

(e)

Disaccommodation factor—the permeability of a magnetic material can also change with time after magnetization. This phenomenon is often called disaccommodation. If the permeabilities μ1 and μ2 correspond to times t1 and t2 then the disaccommodation is given by:

   

μ1μ2

 × 100%

μ1

As with the loss and temperature factors, the disaccommodation factor is normalized to unit permeability and is given by:


   

disaccommodation factor = 

μ1μ2

 × 100%.

μ12




Apart from changes in their magnetic permeability, some materials have other responses to changes in magnetic field strength. All conducting materials exhibit the Hall effect, of which there are two forms. In the transverse Hall effect a voltage is developed in a direction at right angles to a current passing through the material when a magnetic field is applied in a mutually perpendicular direction. The relationship between the current flowing through the material Ix, the output voltage, Vy, the thickness of the material, tz, and the applied magnetic field strength, Hz, is given by:

             Vy = (KH Ix μ0 Hz) /tz

where KH is the transverse Hall coefficient of the material. It has been found that some semiconducting materials have sufficiently high Hall coefficients to produce convenient, small size and low cost magnetic sensors. Indium arsenide having a Hall coefficient of 0.75 Vm/TA is a widely used material.

The same conditions that produce the transverse Hall effect also give rise to a voltage in the direction of the current and this is sometimes called the longitudinal Hall effect but more usually magnetoresistance. Until recently only small changes in resistance have been observed (up to 2% for the widely used Ni80Fe20 material at room temperature) but the so-called giant magnetoresistance (GMR) has been observed in multilayers of Fe/Cr (50% change in resistance) and Co/Cu (120% change in resistance). However, strong magnetic field strengths (≈ 800 kA/m) and a temperature of 4.2 K are required to observe GMR in a multilayer. In all cases the magnetoresistance of a material is a complex function of the applied magnetic field strength, temperature, material type and thickness.

Since the properties may vary considerably from specimen to specimen due to chemical composition and state of heat treatment, the values given are only to be regarded as typical of the materials mentioned. A range of values is indicated by a dash.


Symbols used in tables:

   B   = magnetic flux density
   Br  = remanence
   H   = magnetic field strength
   HcB = induction coercive force, coercivity
   HcJ = magnetization coervice force, coercivity
   J    = magnetic polarization
   Js   = (Bμ0H)s = saturation polarization
   Qh  = hysteresis loss per unit volume per cycle
   μr   = relative magnetic permeability
   μi   = initial relative magnetic permeability



(1) Magnetic susceptibilities of paramagnetic and diamagnetic materials

Values are mass susceptibility per kilogram, χ, at 20°C.

 

× 10−8

spacer  

× 10−8

spacer  

× 10−8

 

 

 

 

 

 

 

 

Common elements

 

 

 

 

 

 

 

Hydrogen   .  .  .  .  .

−2.49

 

Aluminium  .  .  .  .  .

+0.82

 

Germanium  .  .  .  .  .

−0.15

Oxygen.  .  .  .  .  .  .

+133.6    

 

Copper      .  .  .  .  .

  −0.107

 

Silicon   .  .  .  .  .  .  .

−0.16

Helium    .  .  .  .  .  .

−0.59

 

Silver      .  .  .  .  .  .

−0.25

 

Arsenic    .  .  .  .  .  .

−0.39

Neon   .  .  .  .  .  .  .

−0.41

 

Gold       .  .  .  .  .  .

−0.19

 

Indium  .  .  .  .  .  .  .

−0.14

Argon .  .  .  .  .  .  .

−0.60

 

Platinum  .  .  .  .  .  .

+ 1.22

 

Antimony .  .  .  .  .  .

−1.09

Krypton    .  .  .  .  .

−0.41

 

Mercury  .  .  .  .  .  .

−0.21

 

Tellurium  .  .  .  .  .  .

−0.39

Xenon    .  .  .  .  .  .

−0.40

 

Bismuth   .  .  .  .  .  .

−1.70

 

Gallium  .  .  .  .  .  .  .

−0.30

Nitrogen   .  .  .  .  .

−0.54

 

Sulphur   .  .  .  .  .  .

−0.62

 

Phosphorus .  .  .  .  .

−1.13

Sodium     .  .  .  .  .

+0.75

 

Lead   .  .  .  .  .  .  .

−0.15

 

 

 

Potassium .  .  .  .  .

+0.65

 

Uranium .  .  .  .  .  .

+2.19

 

 

 

 

 

 

 

 

 

 

 

Common compounds

 

 

 

 

 

Common materials

 

H2O     .  .  .  .  .  .

−0.90

 

NiSO47H2O   .  .  .

+20.1   

 

Araldite  .  .  .  .  .  .

−0.63

NO      .  .  .  .  .  .

+59.3   

 

NiSO4K2SO47H2O

+13.9   

 

P.V.C    .  .  .  .  .  .

−0.75

CO2     .  .  .  .  .  .

−0.59

 

CuSO45H2O  .  .  .

+ 7.7  

 

Perspex .  .  .  .  .  .

−0.5  

NH3     .  .  .  .  .  .

−1.38

 

MnSO44H2O .  .  .

+81.2   

 

Polyethylene   .  .  .

+0.2  

HCl      .  .  .  .  .  .

−0.75

 

FeSO4(NH4)2   .  .

 

 

 

 

H2SO4    .  .  .  .  .

−0.50

 

   SO46H2O   .  .  .

+40.6   

 

 

 

NaCl    .  .  .  .  .  .

−0.64

 

 

 

 

 

 

NiCl2   .  .  .  .  .  .

 

 

 

 

 

 

 

    (anhydrous)  .  .

+78.5   

 

 

 

 

 

 

    (in solution)  .  .

+43.0   

           

 

 

 

 

 

 

 

 




(2) Feebly magnetic steels and cast irons


Material

Approx.%
composition
(Balance iron)

Condition

μr
for H = 5 kA/m*

ρ

μΩ m

 

 

 

 

 

Aluminium silicon bronze

see BS 2872

as cast

1.001

   CA 12

and BS 2874

 

 

 

Aluminium nickel bronze

see ISO 428

as cast

1.2–1.4

   CA3

 

 

 

High tensile brass CZ114

see BS 2872, BS 2874

as cast

1.05  

   or HT1

and ISO 426

 

 

 

Austenitic stainless steels

 

 

 

   AISI type:

 

 

 

 

301

     Ni 7.8, Cr 17.6

   Austenized

1.003

0.68

 

 

   19.5% cold reduction

1.15  

 

 

 

   55% cold reduction

14.8      

 

302

     Ni 9.0, Cr 18.4

   Austenized

1.003

0.70

 

 

   20% cold reduction

1.008

 

 

 

   44% cold reduction

1.050

 

 

 

   68% cold reduction

1.59  

 

304

     Ni 10.7, Cr 19.0

   Austenized

1.004

0.72

 

 

   13.8% cold reduction

1.005

 

 

 

   32% cold reduction

1.04  

 

 

 

   65% cold reduction

1.55  

 

305

     Ni 11.7, Cr 17.9

   Austenized

1.003

 

 

   18.5% cold reduction

1.004

 

 

 

   52.5% cold reduction

1.05  

 

310

     Ni 20.7, Cr 24.3

   Austenized

1.002

0.94

 

 

   64.2% cold reduction

1.002

 

316

     Ni 13.4, Cr 17.5

   Austenized

1.003

0.74

 

 

   81% cold reduction

1.007

 

321

     Ni 10.3, Cr 18.3, Ti 0.68

   Austenized

1.003

0.72

 

 

   16.5% cold reduction

1.018

 

 

 

   41.5% cold reduction

1.40  

 

347

     Ni 10.7, Cr 18.4, Co 0.95

   Austenized

1.004

0.73

 

 

   13.5% cold reduction

1.007

 

 

   40% cold reduction

1.06  

 

 

 

   60% cold reduction

1.25  

 

 

 

 

 

 




(3) Soft (low coercivity) materials

Material
(approx. % composition , balance iron)

B/T for
H/
(A m−1) =

Relative
permeability μ
r

Js

T

HcB

A m−1

Br

T

Curie
point

°C

Resistivity

10−8 Ωm

Specific total
loss for
J
= 1.5 T,

 

f = 50Hz

W/kg

 

Specific
apparent power
for J
= 1.5 T,

 

f = 50Hz

VA/kg

 

1000

5000

Initial

μi

1000

Maximum

μr

1000

 

 

 

 

 

 

 

 

 

 

 

 

Ferromagnetic elements

 

 

 

 

 

 

 

 

 

 

 

    Iron, high purity (single

 

 

 

 

 

 

 

 

 

 

 

        crystals in preferred direction)  .  .

2.01

2.01

1500

2.16

  12

770

10

    Armco iron      .  .  .  .  .  .  .  .  .  .  .

1.55

1.72

0.25

      7

2.16

  80

1.3

770

11

    Cast iron (annealed)     .  .  .  .  .  .  .

0.60

0.86

1.70

400

 

 

 

    Swedish iron (annealed)     .  .  .  .  .

1.52

1.72

2.16

  70

770

    Nickel      .  .  .  .  .  .  .  .  .  .  .  .  .  .

0.45

0.55

  0.615

400

358

  9

    Cobalt      .  .  .  .  .  .  .  .  .  .  .  .  .  .

0.21

0.70

1.76

950

1115  

  9

 

 

 

 

 

 

 

 

 

 

 

 

Steels (solid)

 

 

 

 

 

 

 

 

 

 

 

   Carbon steel (annealed) 1% C  .  .  .

0.75

1.54

2.00

600

   Constructional steels:

 

 

 

 

 

 

 

 

 

 

 

      0.3% C, 1% Ni

1.32

1.68

2.10

250

      0.4% C, 3% Ni, 1.5% Cr  .  .  .  .

0.75

1.67

2.05

500

   Mild steel, 0.1% C    .  .  .  .  .  .  .

1.46

1.74

2.15

150

10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Steels (sheet)†

 

 

 

 

 

 

 

 

 

 

 

    Grain oriented silicon steels with

 

 

 

 

 

 

 

 

 

 

 

    preferred magnetic properties in

 

 

 

 

 

 

 

 

 

 

 

    direction of rolling of the parent strip

 

 

 

 

 

 

 

 

 

 

 

    (d.c. magnetization):

 

 

 

 

 

 

 

 

 

 

 

    Unisil-H, 103-27-P5, (27MOH) 2.9% Si

1.93

2.00

93

2.00

    6

745

45

1.00 (J = 1.7T)

1.38 (J = 1.7T)

    Unisil,089-27-N5,(27M4)

 

           097-30-N5, (30M5)

3.1%Si

           111-35-N5, (35M6)

 

1.86

1.96

75

2.00

    7

745

48

0.84

1.16

1.86

1.96

59

2.00

    7

745

48

0.89

1.32

1.84

1.94

58

2.00

    7

745

48

1.00

1.39

    Non-oriented silicon steels:

 

 

 

 

 

 

 

 

 

 

 

    SURA   300-35-A5, (CK-37)    2.9% Si

1.46

1.65

  8

2.00

  40

745

48

2.95

28

                 400-50-A5, (CK-40)    2.4% Si

1.48

1.69

  7

2.03

  40

748

44

3.60

19

                 800-65-A5, (DK-70)    1.6% Si

1.53

1.73

  5

2.08

  70

758

34

6.50

14

    Non-oriented, non-silicon steel:

 

 

 

 

 

 

 

 

 

 

 

    Newcor 1000-65-D5  .  .  .  .  .  .  .

1.59

1.75

8

2.15

50

770

12

7.00

9.6

 

 

 

 

 

 

 

 

 

 

 

 

Amorphous iron–boron alloys

 

 

 

 

 

 

 

 

 

 

 

(metallic glass)

 

 

 

 

 

 

 

 

 

 

 

    Metglas‡   2605 S-3 .  .  .  .  .  .  .

1.58

  8

0.7

405

125

0.15 (J = 1.7T)

0.20 (J = 1.0T)

    Metglas†   2605 SC  .  .  .  .  .  .  .

1.61

  5

1.1

370

125

 

 

 

 

 

 

 

 

 

 

 

 

 

 




Material
(approx. % composition , balance iron)

Flux density B/T for H/(A m−1) =

Relative permeability μr

Js

T

HcB

A m−1

Br

T

Curie
point

°C

Resistivity

10−8 Ωm

1.0


10


50


100


1000


50 000


Initial

μi

1000

Maximum

μr

1000

 

       

 

 

 

 

 

 

 

 

 

Nickel iron alloys

       

 

 

 

 

 

 

 

 

 

  Supermumetal§

 

  Nilomag 771

  70–80% Ni with small

  Mumetal plus§

  amounts of other

 

  Mumetal§

  elements

  EPC 20

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.45

0.72

0.76

0.78

200

400

0.77

0.55

0.5  

350

55

 

 

 

 

 

 

 

 

 

 

 

 

 

0.30

0.70

0.75

0.77

  80

300

0.77

0.8 

0.45

350

55

 

 

 

 

 

 

 

 

 

 

 

 

 

0.18

0.60

0.72

0.75

  60

240

0.77

1.0  

0.45

350

55

 

 

 

 

 

 

 

 

 

 

 

 

 

  Nilomag 641        65% Ni + small
                           amount of other
                           elements, oriented

0.4–1.0

200–400

1.4  

4    

1.35

590

48

  Nilomag 471

 

  Super Radiometal§

 

 

  50% Ni + small

  Radio metal 4550§

  amounts of

 

 

  other elements

 
  Satmumetal§  
  HCR alloy§

+oriented structure

       

 

 

 

 

 

 

 

 

 

0.03

1.02

1.25

1.4

1.62

2–11

50–120

1.6

4–12

0.4–1.2

530

43

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.01

0.48

1.05

1.18

1.62

3–6

20–50

1.6

12–24

0.4–1.0

530

50

 

 

 

 

 

 

 

 

 

 

 

 

 

0.20

1.15

1.3  

1.35

65

240

1.5

2.0

0.7

550

60

0.3  

1.46

1.50

1.55

0.5–1.0

50–100

1.6

10

1.5

525

40

  Radio metal 36§

35% Ni 

0.15

0.72

0.90

1.2  

2

15

1.3

12

  0.35

180–270

80

  Hyperm 36

36% Ni

 

constant permeability alloy

1.75

6

  R2799§  30% Ni, temperature

0.1  

  0.45

70

85

 

compensating alloy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cobalt-iron alloys§

 

 

 

 

 

 

 

 

 

 

 

 

 

   Permendur 24  24% Co

0.002

0.02

0.05

1.45

2.34

0.25

2.0

2.35

  950

  1.65

980

20

   Permendur 49  49% Co

0.01  

0.13

0.33

1.85

2.34

1.0  

  7

2.35

  140

1.5

980

47

   Supermendur   49% Co, 2% V

2.05

2.1  

2.3  

2.34

70

2.35

    20

2.1

980

40

   Hisat 50         49% Co, 0.3% Ta

1.5  

1.8  

2.3  

2.44

18

2.44

    40

1.8

980

10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Other alloys

 

 

 

 

 

 

 

 

 

 

 

 

 

   Heusler alloy   61% Cu, 26% Mn, 13% Al 

 0.01

0.25

0.45

0.48

550

330

   Isoperm         30% Ni, 11% Cu

 

constant permeability alloy

0.06

0.065

   Perminvar       40% Ni, 25% Co

 

constant permeability alloy

0.30

1.5   

1.55

100

715

19

   Nickel copper  70% Ni, 30% Cu

0.07

0.15

10–100

         

 

 

 

 

 

 

 

 

 




Material

Initial
relative
permeability

μi

Frequency
range

MHz

Loss factor
at maximum
frequency

10−6

Temperature
factor

10−6 /°C

Flux
density
B/T for
H/(A m−1)
=800

Power loss
density for
B = 0.2T,
f = 16 kHz

mW/cm3

IEC
hysteresis
coefficient

ηB

Disaccommodation
factor

10−6

Curie
point

°C

Resistivity

Ωm

 

 

 

 

 

 

 

 

 

 

 

Carbonyl iron powder cores

 

 

 

 

 

 

 

 

 

 

    type 100

30

0.1–2     

700

20

    type 500

12

1–10

250

12

    type 900

10

1–50

600

12

    type 901

  5

10–100

1500  

12

Magnetic iron oxide powder cores

 

 

 

 

 

 

 

 

 

 

    type 910

  4

20–300

500
(at 100 MHz)

40

Iron flake cores

 

 

 

 

 

 

 

 

 

 

   used for interference
   suppression, relative
   initial permeability
   falls rapidly with
   frequency

90 at 1 kHz

65 at 150 kHz

Ferrite cores

 

 

 

 

 

 

 

 

 

 

   (a) for radio, TV and

 

 

 

 

 

 

 

 

 

 

        low power uses:

 

 

 

 

 

 

 

 

 

 

        nickel zinc,

 

 

 

 

 

 

 

 

 

 

           type F13

650

0.05–1

130

180

  300

           type F14

220

  0.1–2

  50

270

1000

           type F16

125

       1–10

100

270

1000

           type F22

  19

       5–40

500

500

1000

       manganese zinc,

 

 

 

 

 

 

 

 

 

 

           type F10

5000

0.01–0.1

  12

180

0.5

           type F8

1500

0.05–0.5

  80

180

1  

           type F11

  600

0.1–1

  50

220

5  

   (b) perminvar, high

 

 

 

 

 

 

 

 

 

 

        frequency low power

 

 

 

 

 

 

 

 

 

 

        uses

 

 

 

 

 

 

 

 

 

 

            type F25

    50

5–40

300 

450

1000

            type F29

    12

10–200

1000   

500

1000

  (c) manganese zinc for

 

 

 

 

 

 

 

 

 

 

        high power uses

 

 

 

 

 

 

 

 

 

 

            type F6

1500 

0.45

150

180

1

            type F5

2000 

0.48

  75

200

1

   (d) manganese zinc, high

 

 

 

 

 

 

 

 

 

 

        stability, low loss,

 

 

 

 

 

 

 

 

 

 

        telecommunications

 

 

 

 

 

 

 

 

 

 

        uses

 

 

 

 

 

 

 

 

 

 

           type P10

2000

12*  

0–2

2.5

8

150

  1

           type P11

2200

5*

0.5–1.5

0.8

5

150

  1

           type P12

2200

3*

0.4–1.0

0.4

3

150

  1

 

 

 

 

 

 

 

 

 

 

 




(4) Permanent magnet (magnetically hard) materials
     
(a) Typical alloys in the Al–Ni–Co series (cast material):

Material

Approx. composition
(balance iron)

%

Remanence
Br

T

(BH)max

kJ m −3

 

Coercivity

 

Curie
point

°C

Maximum
operating
temperature

°C

Resistivity

μΩ m

HcB

kA m −1

HcJ

kA m −1

 

 

 

 

 

 

 

 

 

Alni

isotropic

Alnico 1

  Ni 25, Al 13, Cu 4

0.56

  10.0

46

49

760

550

0.63

 

 

 

 

 

 

 

 

 

Alnico

isotropic

Alnico 2

  Ni 19, Al 10, Co 12, Cu 6

0.73

  13.5

45

48

800

550

0.65

 

 

 

 

 

 

 

 

 

Alcomax III

anisotropic

Alnico 5

Ni 13.5, Al 8, Co 24, Cu 3

1.30

43

52

53

850

550

0.55

 

 

 

 

 

 

 

 

Alcomax III

semi-columnar

Alnico 5 DG

1.32

49

56

57

860

550

0.55

 

 

 

 

 

 

 

 

Columax

columnar

Alnico 5–7

1.35

60

59

60

860

550

0.55

Hycomax II      anisotropic

  Ni 14.5, Al 7, Co 29,

0.85

32

95

97

850

550

0.50

 

           Cu 4.5, Ti 5

 

 

 

 

 

 

 

Hycomax III

anisotropic

Alnico 8

 

Ni 14, Al 7.3, Co 34,

Cu 3, Ti 5.25

 

0.90

44

127  

129  

850

550

0.50

Alnico 9 columnar

1.05

80

124  

126  

850

550

0.50

 

 

 

 

 

 

 

 

 

Note: The isotropic and anisotropic alloys can also be prepared by sintering, in which case the magnetic properties can be up to 20% less than those for cast material.




(b) Rare-earth alloys:

Material

Type

Remanence
Br

T

(BH)max

KJ m−3

Coercivity

Curie
point

°C

Maximum
operating
temperature

°C

Resistivity

μΩ m

HcB

kA m −1

HcJ

kA m −1

Supermagloy, sintered

               

      —pressed axially

 

 Sm Co5

 

0.90

160

680

1500

725

150

0.70

 

 

 

 

 

 

 

 

      —pressed isostatically

0.95

176

720

1500

725

150

0.70

      —anisotropic

            Sm2Co17

1.05

210

760

700–2000

800

250

0.70

      —bonded

            Sm Co5 + binder

0.58

  56

380

760

*

    60*

10       

 

 

 

 

 

 

 

 

 

Neodure

Sintered

Neorem

anisotropic

 Nd Fe B

1.15–1.35

220–350

880–960

890–1700

300–320

150

1.50

Magnequench, isotropic

 

0.61

64

424

1200

*

    60*

180   

Bemag 5N

NIN 403

 bonded,

 Nd Fe B + binder

 

 

 

 

 

 

 

 injection moulded,

0.40

32

300

600

*

150

 anisotropic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 




(c) Ferrites:

Material

Approx. composition
(balance iron)

%

Remanence
Br

T

(BH)max

kJ m−3

Coercivity

Curie
point

°C

Maximum
operating
temperature

°C

Resistivity

μΩ m

HcB

kA m−1

HcJ

kA m−1

                 

Feroba 1

 sintered isotropic

MMG D1

 
 

BaO + 5.9 (Fe2O3)

 
 
 
 

SrO + 5.9 (Fe2O3)

   

0.22

 8

135

220

450

350

104

 

 

 

 

 

 

 

 

Ferroba 2

 sintered anisotropic

 

 

 

 

 

 

 

Ferroxdure 300

0.39

28

176

184

450

350

104

Feroba 3

 

 

 

 

 

 

 

Ferroxdure 380

0.37

26

240

230

450

350

104

Ferroxdure 500

0.40

30

295

320

450

350

104

Flexam P5
MMG 01

 bonded isotropic

 

0.14

     3.2

  85

175

*

120*

106

Flexor 45

 bonded anisotropic

FXD SP106

 

0.25

   11.2

175

240

*

120*

106

 

 

 

 

 

 

 

 

 




A.E.Drake.

 

 

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