Methods of measurement of the magnetic properties of permanent magnet (magnetically hard) materials in an open magnetic circuit using a superconducting magnet

IEC TR 63304:2021(E) describes the general principle and technical details of the methods of measurement of the DC magnetic properties of permanent magnet materials in an open magnetic circuit using a superconducting magnet (SCM).
This method is applicable to permanent magnet materials, such as those specified in IEC 60404-8-1, the properties of which are presumed homogeneous throughout their volume.
There are two methods:
– the SCM-Vibrating Sample Magnetometer (VSM) method;
– the SCM-Extraction method.
This document also describes methods to correct the influence of the self-demagnetizing field in the test specimen on the demagnetization curve measured in an open magnetic circuit. The magnetic properties are determined from the corrected demagnetization curve.
NOTE These SCM-methods can determine the magnetic properties of permanent magnet materials with coercivity higher than 2 MA/m. The methods of measurement in a closed magnetic circuit specified in IEC 60404-5 can lead to significant measurement error due to saturation effects in the pole pieces of yoke for the magnetic materials with coercivity higher than 1,6 MA/m (see IEC 60404-5).

General Information

Status
Published
Publication Date
25-Apr-2021
Current Stage
PPUB - Publication issued
Completion Date
26-Apr-2021
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IEC TR 63304
Edition 1.0 2021-04
TECHNICAL
REPORT
Methods of measurement of the magnetic properties of permanent magnet
(magnetically hard) materials in an open magnetic circuit using a
superconducting magnet
IEC TR 63304:2021-04(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 63304
Edition 1.0 2021-04
TECHNICAL
REPORT
Methods of measurement of the magnetic properties of permanent magnet
(magnetically hard) materials in an open magnetic circuit using a
superconducting magnet
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20; 29.030 ISBN 978-2-8322-9714-8

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 63304:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 9

2 Normative references ...................................................................................................... 9

3 Terms and definitions ...................................................................................................... 9

4 General principle ........................................................................................................... 11

4.1 Principle of the method ......................................................................................... 11

4.2 Superconducting magnet (SCM)............................................................................ 12

4.3 Magnetic field strength sensor (H sensor) ............................................................. 13

4.4 Magnetic dipole moment detection coil (M coil) ..................................................... 13

4.5 Specimen rod and moving device .......................................................................... 14

4.6 Measuring devices and the data processing device ............................................... 14

5 Test specimen ............................................................................................................... 14

6 Preparation of measurement .......................................................................................... 15

6.1 Measurement of volume of the test specimen ........................................................ 15

6.2 Initial magnetization of the test specimen to saturation ......................................... 15

7 Determination of magnetic polarization .......................................................................... 15

7.1 Measurement of the magnetic dipole moment ....................................................... 15

7.2 Determination of magnetic polarization ................................................................. 16

8 Measurement of magnetic field ...................................................................................... 17

9 Calibration of the magnetic dipole moment detection coil (M coil) .................................. 17

10 Determination of demagnetization curve ........................................................................ 17

11 Demagnetizing field correction ....................................................................................... 18

11.1 General ................................................................................................................. 18

11.2 Method A: Method using a demagnetizing factor determined by the shape of

the test specimen only .......................................................................................... 20

11.3 Method B: Method using a demagnetizing factor determined by the shape

and the magnetic susceptibility of the test specimen ............................................. 20

11.4 Method C: Method using an inverse analysis considering the spatial

distribution of the self-demagnetizing field strength in the test specimen ............... 21

12 Determination of principal magnetic properties .............................................................. 21

12.1 Remanent magnetic polarization J ....................................................................... 21

12.2 Maximum energy product (BH) ........................................................................ 22

max

12.3 Coercivity (H and H ) ...................................................................................... 22

cJ cB

13 Reproducibility ............................................................................................................... 22

14 Test report ..................................................................................................................... 22

Annex A (informative) SCM-Magnetometer method .............................................................. 24

Annex B (informative) Effects of the test specimen dimensions ............................................ 26

Annex C (informative) Superconducting magnets (SCMs) .................................................... 27

Annex D (informative) Magnetic dipole moment detection coils (M coils) .............................. 29

Annex E (informative/normative) Details of the demagnetizing field correction ..................... 31

E.1 General ................................................................................................................. 31

E.2 Symbols ................................................................................................................ 31

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IEC TR 63304:2021 © IEC 2021 – 3 –
E.3 Method using a demagnetizing factor determined by the shape and magnetic

susceptibility of the test specimen (Method B)....................................................... 32

E.4 Method using an inverse analysis considering the spatial distribution of the

self-demagnetizing field strength in the test specimen (Method C) ........................ 34

Annex F (informative) Result of the international round robin test of magnetic

properties of permanent magnets using the SCM-VSM and SCM-Extraction methods ........... 39

F.1 General ................................................................................................................. 39

F.2 Protocol of the RRT .............................................................................................. 39

F.3 Result of the RRT ................................................................................................. 40

F.4 Reproducibility of the measurements .................................................................... 43

Bibliography .......................................................................................................................... 45

Figure 1 – Demagnetization curve J(H) ................................................................................. 10

Figure 2 – Schematic diagrams of the test apparatus ............................................................ 11

Figure 3 – Schematic diagrams of the first order gradiometer coil ......................................... 13

Figure 4 – Relationship between magnetic polarization and self-demagnetizing field ............ 18

Figure 5 – Schematic diagram of the demagnetizing field correction ..................................... 19

Figure 6 – Conceptual diagram of the procedure of Method C ............................................... 21

Figure A.1 – Schematic diagram of the test apparatus for the SCM-Magnetometer

method ................................................................................................................................. 24

Figure A.2 – Schematic diagrams of the test apparatus for the method in a closed

magnetic circuit in accordance with IEC 60404-5 .................................................................. 25

Figure B.1 – Effects of test specimen dimensions on magnetic properties [B , H , H

r cJ cB

and (BH) ] for Nd-Fe-B sintered magnets with different coercivities ................................. 26

max

Figure C.1 – Typical cross-sectional structure of the ceramic SCM ....................................... 28

Figure D.1 – Schematic diagram of the second order gradiometer coil for the SCM-

VSM method ......................................................................................................................... 29

Figure D.2 – Schematic diagram of the dependence of induced voltage on the position

of the test specimen in the SCM-Extraction method .............................................................. 30

Figure E.1 – Axes of a cuboid magnet ................................................................................... 32

Figure E.2 – Conceptual diagram of the procedure of Method C............................................ 35

Figure E.3 – Flowchart of the procedure of Method C ........................................................... 36

Figure E.4 – Comparison of the demagnetization curves corrected using demagnetizing

field correction Methods A, B and C ...................................................................................... 38

Figure F.1 – Comparison of J measured by the laboratories ................................................. 40

Figure F.2 – Comparison of H measured by the laboratories ............................................. 41

Figure F.3 – Comparison of (BH) measured by the laboratories ...................................... 41

max

Figure F.4 – Comparison of hysteresis loops measured by the laboratories .......................... 43

Figure F.5 – Relative standard deviation of J , H and (BH) .......................................... 44

r cJ max

Table 1 – Features of the demagnetizing field correction methods in comparison with

Method B .............................................................................................................................. 20

Table 2 – Reproducibility of the magnetic properties ............................................................. 22

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– 4 – IEC TR 63304:2021 © IEC 2021

Table C.1 – Performance of SCMs ........................................................................................ 27

Table F.1 – Nominal values of coercivity ............................................................................... 39

Table F.2 – Participating laboratories and their employed measuring methods ...................... 40

Table F.3 – Comparison of magnetic properties measured by the laboratories ...................... 42

Table F.4 – Comparison of the reproducibility ....................................................................... 44

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IEC TR 63304:2021 © IEC 2021 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHODS OF MEASUREMENT OF THE MAGNETIC PROPERTIES OF
PERMANENT MAGNET (MAGNETICALLY HARD) MATERIALS IN AN OPEN
MAGNETIC CIRCUIT USING A SUPERCONDUCTING MAGNET
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC TR 63304 has been prepared by IEC technical committee 68: Magnetic alloys and steels.

It is a Technical Report.
The text of this Technical Report is based on the following documents:
DTR Report on voting
68/675/DTR 68/680/RVDTR

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this Technical Report is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.
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– 6 – IEC TR 63304:2021 © IEC 2021

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under webstore.iec.ch in the data related to the

specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 8 ----------------------
IEC TR 63304:2021 © IEC 2021 – 7 –
INTRODUCTION

Permanent magnet materials with high coercivity e.g. Nd-Fe-B magnets, have been used in

industry and its usage increases rapidly to meet demands to improve energy saving and to

increase efficiency of electromagnetic applications, e.g. traction motors for Electric Vehicle (EV)

and Hybrid Electric Vehicle (HEV).

However, there is no standard method which can determine all the magnetic properties of the

permanent magnet materials with coercivity H higher than 2 MA/m. The method specified in

IEC 60404-5, which is a method of measurement in a closed magnetic circuit, can lead to

significant measurement errors for measurement of H ≥ 1,6 MA/m due to magnetic saturation

in parts of the pole faces of the yoke (see IEC 60404-5).

In order to solve the problem, several methods of measurement in an open magnetic circuit

using a superconducting magnet (SCM) without a yoke have been developed. The methods

using a SCM have been considered to be candidates for solution to accurate measurement of

high performance permanent magnets.

The method using a conventional SCM made of metallic superconducting coil has not been

used widely for industrial applications due to costs for using expensive liquid helium, limited

speed of variation of magnetic field strength, and the difficulty to deal with test specimens of

industrial size.

However, nowadays these problems have been solved thanks to the development of a ceramic

SCM made of ceramic high temperature superconducting coil. This method has enabled the

higher speed of variation of magnetic field strength without using precious resource of liquid

helium (see Annex C). Furthermore, test apparatus using the ceramic SCM which can treat test

specimens of industrial size have been commercialized globally for industrial use.

However, results of measurement in an open magnetic circuit are different from those of

measurement in accordance with IEC 60404-5, particularly in terms of the squareness of

demagnetization curves. This is caused by the influence of the self-demagnetizing field in the

test specimen, which is opposed to magnetization. This is particular to the measurement in an

open magnetic circuit. Therefore, a correction of the influence of self-demagnetizing field

(demagnetizing field correction) on the demagnetization curve measured in an open magnetic

circuit is indispensable.

This document describes three methods of measurement in an open magnetic circuit using a

superconducting magnet (SCM), as follows:
a) SCM-Vibrating Sample Magnetometer (VSM) method;
b) SCM-Extraction method;
c) SCM-Magnetometer method.

In these methods, a test specimen is placed in a detection coil placed in a uniform magnetic

field generated by a SCM. For methods a) and b), the magnetic dipole moment of the test

specimen is detected by voltage induced in the detection coil due to a vibration and an

extraction of the test specimen, respectively. For the method c), a variation of magnetic

polarization of a stationary test specimen is detected by voltage induced in the detection coil

due to a variation of the magnetic field strength applied to the test specimen.

The reproducibility of measurements of the methods a) and b) has been confirmed by an

international round robin test (RRT) that was comparable with that of IEC 60404-5 (see

Annex F). However, the reproducibility of the method c) has not been confirmed by a RRT yet.

Therefore, the method c) is described separately in Annex A.
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– 8 – IEC TR 63304:2021 © IEC 2021

There is another method of the measurement in an open magnetic circuit, i.e. the pulsed field

magnetometer (PFM), which is described in IEC TR 62331 [1] . The PFM is different from the

methods described in this document. The PFM measures a steep AC magnetic response of a

test specimen in a pulsed current magnetic field. Consequently, additional correction is

indispensable due to the influence of eddy currents in the test specimen and the magnetic

viscosity of the magnetic materials.

A demagnetization curve should be measured by decreasing the magnetic field strength with a

sufficiently slow speed during the reversal of the polarization to avoid significant magnetic

viscosity and eddy current effects in accordance with IEC 60404-5. In the case of adopting a

conventional metallic SCM made of metallic superconducting coil, the speed of variation of the

magnetic field is too slow so that it takes an hour to obtain a demagnetization curve because

of a limit of variation rate of the magnetic field to maintain the coil in a superconducting state.

The problem has been solved by adopting a newly developed ceramic SCM made of ceramic

high temperature superconducting coil so that a demagnetization curve can be measured within

several minutes (see Annex C).

A new method of the demagnetizing field correction has been developed (see Annex E). It is a

finite element method (FEM) considering the spatial distribution of self-demagnetizing field

strength in the test specimen. The squareness of the corrected demagnetization curve is

comparable with that measured in accordance with IEC 60404-5.
___________
Numbers in square brackets refer to the Bibliography.
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IEC TR 63304:2021 © IEC 2021 – 9 –
METHODS OF MEASUREMENT OF THE MAGNETIC PROPERTIES OF
PERMANENT MAGNET (MAGNETICALLY HARD) MATERIALS IN AN OPEN
MAGNETIC CIRCUIT USING A SUPERCONDUCTING MAGNET
1 Scope

This Technical Report describes the general principle and technical details of the methods of

measurement of the DC magnetic properties of permanent magnet materials in an open

magnetic circuit using a superconducting magnet (SCM).

This method is applicable to permanent magnet materials, such as those specified in

IEC 60404-8-1, the properties of which are presumed homogeneous throughout their volume.

There are two methods:
– the SCM-Vibrating Sample Magnetometer (VSM) method;
– the SCM-Extraction method.

This document also describes methods to correct the influence of the self-demagnetizing field

in the test specimen on the demagnetization curve measured in an open magnetic circuit. The

magnetic properties are determined from the corrected demagnetization curve.

NOTE These SCM-methods can determine the magnetic properties of permanent magnet materials with coercivity

higher than 2 MA/m. The methods of measurement in a closed magnetic circuit specified in IEC 60404-5 can lead to

significant measurement error due to saturation effects in the pole pieces of yoke for the magnetic materials with

coercivity higher than 1,6 MA/m (see IEC 60404-5).
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60404-5, Magnetic materials – Part 5: Permanent magnet (magnetically hard) materials –

Methods of measurement of magnetic properties

IEC 60404-8-1, Magnetic materials – Part 8-1: Specifications for individual materials –

Magnetically hard materials

IEC 60050-121, International Electrotechnical Vocabulary – Part 121: Electromagnetism

IEC 60050-151, International Electrotechnical Vocabulary – Part 151: Electrical and magnetic

devices

IEC 60050-221, International Electrotechnical Vocabulary – Chapter 221: Magnetic materials

and components
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050-121,

IEC 60050-151, IEC 60050-221 and the following apply.
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– 10 – IEC TR 63304:2021 © IEC 2021

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
demagnetization curve

part of a hysteresis loop in which the magnetic polarization goes from the remanent magnetic

polarization to zero when the applied magnetic field strength varies monotonically, as illustrated

in Figure 1
Key
J saturation magnetic polarization, in T
J remanent magnetic polarization, in T
H coercivity relating to the magnetic polarization, in A/m
Figure 1 – Demagnetization curve J(H)

Note 1 to entry: A demagnetization curve can be measured from near magnetic saturation.

[SOURCE: IEC 60050-121:1998, 121-12-72, modified – magnetic flux density is replaced by

magnetic polarization and Note 1 to entry and Figure 1 have been added]
3.2
magnetic dipole moment
vector quantity given by the volume integral of the magnetic polarization

[SOURCE: IEC 60050-221:1990, 221-01-07, modified – the symbol j is changed to m which is

used industrially and the note has been removed]
3.3
M coil
detection coil for magnetic dipole moment
3.4
J coil
detection coil for magnetic polarization
---------------------- Page: 12 ----------------------
IEC TR 63304:2021 © IEC 2021 – 11 –
4 General principle
4.1 Principle of the method

Figure 2 illustrates schematic diagrams of typical test apparatuses. The test apparatus consists

of a superconducting magnet (SCM), a moving device, a specimen rod, a magnetic field sensor

(hereafter H sensor), a magnetic dipole moment detection coil (hereafter M coil), measuring

devices and a data processing device (PC). The measurement is carried out in an open

magnetic circuit to enable the determination of magnetic properties of permanent magnet

materials with coercivity higher than 2 MA/m.

The axis of the DC magnetic field generated by the SCM is vertical and coaxial with the M coil

and the specimen rod. The moving test specimen is placed in a zone where the magnetic field

strength is uniform with a tolerance of ±1 % at the centre of the SCM. The H sensor is placed

in a zone where the influence of the magnetic dipole moment of the test specimen can be

ignored.

A test specimen is firmly attached on the specimen rod so that the direction of magnetization is

parallel to the axis of the specimen rod, and then placed in the test apparatus as shown in

Figure 2.
a) The SCM-VSM method b) The typical SCM-Extraction method
Figure 2 – Schematic diagrams of the test apparatus

The test specimen is initially magnetized to saturation (see 6.2), and then a DC magnetic field

is applied to the test specimen in the direction opposite to that used for the initial magnetization.

The magnetic field strength is measured by the H sensor (see 4.3).
---------------------- Page: 13 ----------------------
– 12 – IEC TR 63304:2021 © IEC 2021

The magnetic dipole moment of the test specimen is detected by the voltage induced in the M

coil due to the movement of the test specimen (see 4.4). The magnetic polarization of the test

specimen is calculated from the magnetic dipole moment and the volume of the test specimen

(see 7.2). For calibration aspects, see Clause 9.
There are two methods different in modes of the movement of the test specimen:

a) the SCM-VSM method: the test specimen is vibrated with a small amplitude in the M coil;

b) the SCM-Extraction method: the test specimen is extracted through the M coil.
NOTE There is another method to determine the magne
...

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