IEC TR 62517:2009

IEC/TR 62517 ®
Edition 1.0 2009-04
TECHNICAL
REPORT
Magnetizing behaviour of permanent magnets

IEC/TR 62517:2009(E)
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IEC/TR 62517 ®
Edition 1.0 2009-04
TECHNICAL
REPORT
Magnetizing behaviour of permanent magnets

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
R
ICS 29.030 ISBN 978-2-88910-752-0
– 2 – TR 62517 © IEC:2009(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Effective magnetizing field strength .7
3 Initial magnetization state.8
4 Magnetizing behaviour of permanent magnets .8
4.1 General .8
4.2 Nucleation type magnets, sintered Ferrites, RE-Fe-B, SmCo .9
4.2.1 General .9
4.2.2 Initial magnetization curve after final heat treatment .9
4.2.3 Approach to saturation after final heat treatment .9
4.2.4 Coercivity mechanism of nucleation type magnets .11
4.2.5 Reversing the magnetization after magnetic saturation .12
4.3 Pinning type magnets, Sm Co .13
2 17
4.3.1 General .13
4.3.2 Initial magnetization curve .13
4.3.3 Approach to saturation .14
4.3.4 Coercivity mechanism of pinning type magnets.15
4.4 Single domain particle magnets.16
4.4.1 General .16
4.4.2 Single domain particle magnets based on magnetocrystalline
anisotropy .16
4.4.3 Alnico and CrFeCo magnets .16
5 Conclusions.17
Bibliography.19

Figure 1 – Principal magnetizing behaviour of RE-TM magnets after final heat
treatment .8
Figure 2 – Magnetizing behaviour of sintered Nd-Dy-Fe-B magnets .9
Figure 3 – Magnetizing behaviour of sintered Nd-Dy-Fe-B magnets with various
remanence B and coercivity H values after final heat treatment .11
r cJ
Figure 4 – Magnetizing behaviour of sintered Nd-Dy-Fe-B magnets with various
remanence B and coercivity H values after magnetic saturation in the reverse
r cJ
direction.12
Figure 5 – Magnetizing behaviour of sintered Sm Co magnets with a coercivity H of
2 17 cJ
about 800 kA/m.13
Figure 6 – Magnetizing behaviour of sintered Sm Co magnets with a coercivity H of
2 17 cJ
about 2 800 kA/m.14
Figure 7 – Magnetizing behaviour of sintered Sm-Co magnets with various remanence
B and coercivity H values, left: after final heat treatment and right: after magnetic
r cJ
saturation in the reverse direction .15
Figure 8 – Magnetization behaviour of bonded anisotropic HDDR RE-Fe-B magnets
compared to a sintered anisotropic RE-Fe-B magnet .16

TR 62517 © IEC:2009(E) – 3 –
Table 1 – The recommended internal magnetizing field strengths, H , to achieve
mag
complete saturation for modern permanent magnets, starting from the initial state after
the final heat treatment .18

– 4 – TR 62517 © IEC:2009(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MAGNETIZING BEHAVIOUR OF PERMANENT MAGNETS

FOREWORD
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62517, which is a technical report, has been prepared by IEC technical committee 68:
Magnetic alloys and steels.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
68/377/DTR 68/384/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

TR 62517 © IEC:2009(E) – 5 –
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

– 6 – TR 62517 © IEC:2009(E)
INTRODUCTION
The full performance of a permanent magnet can only be obtained if it is magnetized properly
to saturation. In IEC 60404-5 a definition of the saturation of a permanent magnet is given.
Accordingly, a magnet is defined as saturated at a magnetizing field strength H if a 50 %
higher field strength leads to an increase of (BH) or H of less than 1 %. However, such a
max cB
definition cannot explain the substantial differences in the magnetizing behaviour of modern
permanent magnets which is mainly determined by their coercivity mechanisms. Unfortunately
the variety of magnetizing behaviours cannot be accommodated by a simple recommendation
such as “magnetize with magnetizing field strengths of three to five times the coercivity H ”.
cJ
In particular for RE permanent magnets with high coercivity H this simplification would lead
cJ
to unacceptable overestimations of the required magnetizing field strengths.

TR 62517 © IEC:2009(E) – 7 –
MAGNETIZING BEHAVIOUR OF PERMANENT MAGNETS

1 Scope
It is within the scope of this technical report to describe the magnetizing behaviour of
permanent magnets in detail. Firstly, in Clause 3 the relationship between the applied
magnetic field strength and the effectively acting internal field strength is reviewed. In Clause
4 the initial state prior to magnetization is discussed. Then, in the main Clause 5, the
magnetizing behaviour of all common types of permanent magnets is outlined. The clause is
subdivided according to the dominant coercivity mechanisms, namely the nucleation type for
sintered Ferrites, RE-Fe-B and SmCo magnets, the pinning type for carbon steel and
Sm Co magnets and the single domain type for nano-crystalline RE-Fe-B, Alnico and Cr-
2 17
Fe-Co magnets. Finally, the recommended magnetizing field strengths for modern permanent
magnets are compiled in a comprehensive table.
2 Effective magnetizing field strength
For magnetization of permanent magnets, the internal magnetic field strength H in the
int
magnet is the critical parameter. The internal field strength is determined by the applied field
strength H and the self-demagnetizing field strength H of the magnet or the magnet
appl demag
assembly. The self-demagnetizing field strength depends on the dimensions of the magnet or
the load line of a magnet assembly and the polarization of the magnet material, see equation
(1):
H = H – H = H – N·J/μ (1)
int appl demag appl 0
N denotes the demagnetization coefficient and J the polarization of the magnet material.
Most advanced magnets are magnetized by a short pulse field, achieved by discharging a
capacitor bank through a copper coil. The duration of the field pulse must last sufficiently
long, in order to overcome the eddy currents at the surface of the magnets, in particular for
large blocks. In general, a pulse duration of 5 ms to 10 ms is sufficient for complete
penetration. The penetration depth λ , see equation (2), depends on the electrical resistance
ρ, the permeability μ of the magnet material and the frequency f of the field pulse [1] :
ρ
λ = K ⋅ (2)
μ ⋅ f
K denotes a constant.
Preferably, magnets will be magnetized after assembly, since handling of unmagnetized
magnets is easier and prevents contamination by ferromagnetic particles. In addition chipping
of magnet-edges due to the mutual attraction of magnet parts is avoided.
___________
The composition Sm Co is used as the generic name for a series of binary and multiphase alloys with
2 17
nd
transition elements such as Fe, Cu and Zr replacing Co, see also IEC 60404-8-1; 2 edition 2001.
The figures in brackets refer to the Bibliography.

– 8 – TR 62517 © IEC:2009(E)
3 Initial magnetization state
For nucleation type ferrite, SmCo5 and REFeB magnets, the initial state prior to magnetizing
is usually the state after the final heat treatment, i.e. after sintering. This state shows no net
remanent magnetization and is often called the thermally demagnetized, or virgin, state.
Ferrite and REFeB magnets, once magnetized, may be reset to the initial state by heating
them to above the Curie temperature. This will return them to the thermally demagnetized
state without permanent loss of properties. SmCo magnets can be reset to the initial state
only by repeating the full final heat treatment. To prevent chemical changes which can lead to
surface damage and permanent loss of properties, rare earth magnets shall be protected in
an inert atmosphere during this procedure.
For anisotropic Alnico and CrFeCo magnets, where heat treatment in a magnetic field and
tempering are involved, some residual magnetization may remain in the magnets. These
magnets may be completely demagnetized from any degree of magnetization by applying a
slowly reducing alternating magnetic field. The same holds for any pinning or single domain
type magnet such as Sm Co and rapidly quenched or HDDR-treated REFeB magnets.
2 17
4 Magnetizing behaviour of permanent magnets
4.1 General
The magnetizing behaviour of permanent magnets is closely related to their coercivity
mechanisms, therefore they need to be discussed. Modern permanent magnets may be
divided into three groups with respect to their coercivity mechanism. The principal
magnetization behaviour for these groups, the nucleation type, the pinning type and the single
domain particle type is illustrated in Figure 1.

Sm Co magnet,
Sm Co magnet,
22 1717
H = 800 kA/m
H = 800 kA/m
cJcJ
Sintered
sintered
anisotropic
Nd-Fanisotropice-B
1,0 1,0
1,0 magnet 1,0
Nd-Fe-B
magnet
rapidly
solidified
0,5 0,5
0,5
0,5
Nd-Fe-B
Rapidly
soribbonlidified
Nd-Fe-B
ribbon
Sm Co magnet,
2 17
Sm Co magnet,
2 17
H = 2070 kA/m
cJ
H = 2 070 kA/m
cJ
0,0,0 0 0,0
0,0
0 500 1 000 0 1 000 2 000 3 000
0 500 1000
0 1000 2000 3000
Field strength H in kA/m Field strength H in kA/m
field strength H in kA/m
IEC  523/09 IEC  524/09
field strength H in kA/m
(a)     (b)
a) Nucleation-type anisotropic RE-TM magnets, for instance sintered Nd-Fe-B or SmCo
magnets, or single domain particle type isotropic nanocrystalline RE-TM magnets, for
instance rapidly solidified Nd-Fe-B ribbons
b) Pinning-type RE-TM magnets, for instance Sm Co magnets with coercivities H of
2 17 cJ
800kA/m or 2 070 kA/m, respectively.
Figure 1 – Principal magnetizing behaviour of RE-TM magnets after final heat treatment
Polarization in T
polarization in T
Polarization in T
polarization in T
TR 62517 © IEC:2009(E) – 9 –
4.2 Nucleation type magnets, sintered Ferrites, RE-Fe-B, SmCo
4.2.1 General
The commercially very important sintered Ferrites, RE-Fe-B and SmCo magnets are
nucleation type materials. In the following discussion, the magnetization behaviour of
nucleation type magnets will be discussed using anisotropic sintered RE-Fe-B magnets as an
example.
4.2.2 Initial magnetization curve after final heat treatment
For nucleation type magnets such as sintered Ferrites and Rare Earth Transition Metal (RE-
TM) magnets based on Nd-Fe-B or SmCo , the grains contain multiple magnetic domains
after final heat treatment. The magnetic domains are separated by domain walls which can
move easily within the grains, so that the polarization increases steeply, even in small
magnetizing fields, see Figure 1 a) [2]. For sintered RE-Fe-B magnets, a polarization of about
95 % of the saturation polarization results even after magnetizing with a small magnetizing
field strength of about 200 kA/m.
4.2.3 Approach to saturation after final heat treatment
The polarization decreases, once a low magnetizing field is removed, since no significant
coercivity H has been developed. In the multidomain grains, the domain walls are free to
cJ
move back toward their original positions, to minimize the magnetic stray field energy, see
Figure 2.
-1
Magnetizing field strength H in kA/m
mag
magnetizing field strength H in kA m :
1,5
mag
1,5
1 600
1,1,00
0,5
0,5
375375 300 300
0,0,0 0
–1 500 –1 000 –500 0 500
-1500 -1000 -500 0 500
-1
magnetic field strength in kA m
Magnetic field strength in kA/m

IEC  525/09
Figure 2 – Magnetizing behaviour of sintered Nd-Dy-Fe-B magnets

Polarization J in T
polarization J in T
– 10 – TR 62517 © IEC:2009(E)
The demagnetization curves J(H) were measured on different samples, each in the state after
the final heat treatment, after magnetization by the indicated field strengths H . For
mag
complete magnetization an applied field of 2 000 kA/m is recommended.
Magnetization by a field strength of about 500 kA/m saturates some grains, resulting in some
coercivity. Such grains do not contain domain walls anymore. Since most of the grains are still
multidomain, the J(H) demagnetization curves of such partially magnetized magnets show a
very poor squareness, see Figure 2.
To saturate a nucleation type magnet after final heat treatment, all domain walls within every
single grain must be removed. To achieve this, the internal field strength must become
positive at every point in the material, since strong local demagnetizing stray fields can occur
at the grain edges [3,4]. The magnitude of the local stray fields can be estimated from the
following equation:
H = – N ·J/μ (3)
local eff 0
J denotes the polarization of the magnet material and N presents an effective
eff
demagnetization coefficient, which depends on the local microstructure. In practice, N can
eff
be of the order of two [4]. As a result, perfect saturation requires a magnetizing field strength
of at least twice the saturation polarization J (divided by μ ) of the magnet material [4,5]. For
s 0
the RE-Fe-B magnet shown in Figure 2, complete magnetization requires a strong internal
field strength of more than 1 600 kA/m. In that case, nearly every grain is saturated: hardly
any grains contain small reversed domains.
In conclusion, the internal magnetizing field strength for complete saturation of anisotropic
nucleation type permanent magnets after final heat treatment can be written as
H ≈ 2·J /μ (4)
mag s 0
where J denotes the saturation polarization of the magnet material. The factor 2 describes
s
the effect of the local stray fields as discussed above. It is worth mentioning that the
magnetizing field strength required to saturate such magnets does not depend on the
coercivity H at all, but instead it increases with increasing remanent polarization, see Figure
cJ
3 and Reference [6].
TR 62517 © IEC:2009(E) – 11 –
B/μ H = –1,17
Br = 1,40 T
H = 1 180 kA/m
cJ
Br = 1,35 T
H = 1 500 kA/m
cJ
Br = 1,27 T
H = 1 790 kA/m
cJ
Br = 1,21 T
H = 2 440 kA/m
cJ
0 500 1 000 1 500 2 000 2 500
External magnetizing field strength  (kA/m)
IEC  526/09
Figure 3 – Magnetizing behaviour of sintered Nd-Dy-Fe-B magnets with various
remanence B and coercivity H values after final heat treatment
r cJ
The open circuit flux was measured with a Helmholtz coil after each magnetizing pulse and
related to the remanent flux density after saturation with 4 780 kA/m.
However, the magnetizing
...