ASTM A894/A894M-00(2011)e1
(Test Method)Standard Test Method for Saturation Magnetization or Induction of Nonmetallic Magnetic Materials (Withdrawn 2017)
Standard Test Method for Saturation Magnetization or Induction of Nonmetallic Magnetic Materials (Withdrawn 2017)
ABSTRACT
This test method deals with the standard practice of measuring saturation magnetization or induction of nonmetallic magnetic materials using a vibrating sample magnetometer, which could be commercially purchased from a manufacturer or constructed with normal machine shop facilities. The test specimen shall preferably be in the form of an isotropic sphere, the size of which shall depend on the measuring apparatus. Details concerning equipment setup and calibration, the measurement procedure, and the governing equations for numerical calculations are all discussed thouroughly.
SCOPE
1.1 This test method covers the measurement of saturation magnetization of magnetic materials using a vibrating sample magnetometer.
1.2 Explanation of symbols and abbreviated definitions appear in the text of this test method. The official symbols and definitions are listed in Terminology A340.
1.3 The values stated in either customary (absolute (or practical) cgs-emu) units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with this method.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
WITHDRAWN RATIONALE
This test method covered the measurement of saturation magnetization of magnetic materials using a vibrating sample magnetometer.
Formerly under the jurisdiction of Committee A06 on Magnetic Properties, this test method was withdrawn in April 2017. This standard is being withdrawn without replacement due to its limited use by industry.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: A894/A894M − 00 (Reapproved 2011)
Standard Test Method for
Saturation Magnetization or Induction of Nonmetallic
Magnetic Materials
This standard is issued under the fixed designationA894/A894M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Updated 6.3 and 6.3.2 editorially in October 2011.
1. Scope 3. Summary of Test Method
3.1 The magnetic induction B, magnetic field strength H,
1.1 This test method covers the measurement of saturation
and magnetization M in a material are related by the following
magnetization of magnetic materials using a vibrating sample
equation (1):
magnetometer.
B 5 H14πM ~cgsunits!
1.2 Explanation of symbols and abbreviated definitions
B 5 µ H1M SIunits
~ ! @ #
o
appear in the text of this test method. The official symbols and
definitions are listed in Terminology A340. 3.1.1 In this test method, cgs units are given in parentheses
( ) and SI units in square brackets [ ].
1.3 The values stated in either customary (absolute (or
3.2 The magnetization M is the magnetic moment per unit
practical) cgs-emu) units or SI units are to be regarded
volume of material. In a ferromagnetic or ferrimagnetic
separately as standard. Within the text, the SI units are shown
material, M increases with the applied magnetic field H, but at
in brackets. The values stated in each system are not exact
sufficiently high values of H, M approaches a constant maxi-
equivalents;therefore,eachsystemshallbeusedindependently
mum value called the saturation magnetization M (emu/cm )
s
of the other. Combining values from the two systems may
or[A/m].ThecorrespondingvalueofB−H =4πM (gauss)or
s
result in nonconformance with this method.
B−µ H=µ M [tesla] is called the saturation induction.Itis
o o s
1.4 This standard does not purport to address all of the sometimes given the label B .
s
safety concerns, if any, associated with its use. It is the
3.3 If a sphere of isotropic magnetic material is placed in a
responsibility of the user of this standard to establish appro-
uniform magnetic field, the sphere becomes uniformly magne-
priate safety and health practices and determine the applica-
tized in a direction parallel to the applied field. The magnetic
bility of regulatory limitations prior to use.
field in the space outside the sphere is exactly that of a
magneticdipolelocatedatthecenterofthesphereandoriented
2. Referenced Documents
parallel to the magnetization of the sphere.The strength of this
magnetic dipole is equal to the total magnetic moment of the
2.1 ASTM Standards:
sphere, which is given by:
A340Terminology of Symbols and Definitions Relating to
m 5 Mv emu or A·m
~ ! @ #
Magnetic Testing
where:
3 3
v = is the volume of the sphere, (cm)or[m ].
This test method is under the jurisdiction of ASTM Committee A06 on
Section 4 describes an apparatus that provides an indication
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
or reading proportional to the strength of this dipole field and
Methods.
therefore proportional to the magnetization M of the sample. If
Current edition approved Oct. 1, 2011. Published December 2011. Originally
approved in 1970 as F133. Redesignated as A894. Last previous edition approved
the proportionality constant between this reading and the
in 2005 as A894/A894M–00(2005). DOI: 10.1520/A0894_A0894M-00R11E01.
magnetic moment can be established, and if the volume of the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the back of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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A894/A894M − 00 (2011)
sample is known, the magnetization of the sample is deter- effects of any time-varying fields other than those caused by
mined. Then if the sample can be shown to be magnetically theoscillationofthesample.Foradiscussionofthedesignand
saturated, the saturation magnetization is determined. placement of these coils, see Refs 3 and 4. The coils typically
contain hundreds or thousands of turns to increase the ampli-
4. Apparatus
tude of the induced voltage. The signal may be amplified by a
tuned amplifier whose gain is maximum at the frequency of
4.1 The equipment used for the measurement is called a
oscillation, or preferably by a lock-in amplifier operated at the
vibrating sample magnetometer (2) and is illustrated schemati-
oscillation frequency. The coils may be connected in series or
cally in Fig. 1. The sample is attached to the end of a
as parallel inputs to a differential amplifier; the latter has some
nonmagnetic, nonconducting rod, and placed in a uniform
practical advantages. The output of the tuned amplifier will be
transverse magnetic field generated by an electromagnet or
an ac voltage, while the output of the lock-in amplifier will be
solenoid. The sample and rod are oscillated or vibrated in a
a dc voltage.
direction perpendicular to the field. This oscillating drive may
4.1.3 If a superconducting solenoid is used to provide the
be produced by attaching the end of the sample rod to a
magnetic field, it is usually most convenient to have the
loudspeaker cone or a similar electromagnetic oscillator and
direction of sample vibration parallel rather than perpendicular
driving the loudspeaker coil with an appropriate ac current.
to the field. The operation of the instrument is basically
Alternatively, the rod may be oscillated by a mechanical crank
unchanged,andalltheprovisionsofthisstandardapplytoboth
or cam driven by a small motor. The frequency and amplitude
cases.
oftheoscillationmustbeheldconstant,eitherbythemechani-
cal design of the apparatus or by an appropriate feedback
4.2 One version of the vibrating sample magnetometer uses
system.Theoperatingfrequencyisusuallychosenintherange
a second set of coils placed outside the magnetizing field and
30to100Hz,andtheamplitudeisusuallychosentobe0.01to
a standard sample comprising a small permanent magnet
0.1 cm [0.1 to 1 mm]. The operating frequency should not be
attached to the sample rod (see Fig. 2). In this case, the signal
an integer multiple of the power frequency to avoid pickup of
from the permanent magnet can be balanced against the signal
spurious signals.
from the sample, so that the apparatus is operated in a null
4.1.1 One or more coils are placed symmetrically with
mode. Alternatively, the output from the second set of coils
respect to the sample, oriented so that the moving dipole field
may simply be used to monitor or control the amplitude of the
of the sample produces a changing magnetic flux in the coils.
The resulting ac voltage in the coils is amplified and measured
and is proportional to the dipole moment of the sample and
therefore to the magnetization of the sample.
4.1.2 Various coil orientations are possible. In general, the
coil positions and coil connections are chosen to cancel the
FIG. 2Ref, Reference Standard (Permanent Magnet); C , C , Mea-
1 2
FIG. 1S, Sample; R, Mounting Rod; D, Oscillating Drive Mecha- suring Coils; M, Null-Indicating Meter; Res, Calibrated Variable
nism; P, Magnet Pole Pieces; C, Measuring Coils Resistor. Other Parts as in Fig. 1
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A894/A894M − 00 (2011)
samplevibration.Avariablegapcapacitor,withoneplatefixed k 5 M v /S emu/V or A·m /V
~ ! @ #
ref ref ref
and one attached to the sample rod, can be used to control the
An unknown sample of volume v is measured with all
amplitude of vibration in place of a second set of coils plus a
experimental conditions held constant, giving signal S. Then
magnet.
the magnetization of the unknown sample is given by:
4.3 An advantage of the vibrating sample magnetometer is
M 5 kS/v emu/cm or @A/m#
~ !
that the sample temperature may be easily raised or lowered
with simple heaters or refrigerators. Some precautions are
6.1.2 Iftheimageeffectissignificant, kmustbedetermined
necessary in this case, but they are not a part of this test
as a function of the applied field H.Any variation in k will be
method.
a function only of H, not of the magnetization of the sample or
4.4 Vibrating sample magnetometers are commercially of the standard. However, the size of the standard and of the
available from several manufacturers in various countries, or
unknown sample should be similar, especially if neither is
can be constructed with normal machine shop facilities.
spherical.
6.1.3 Nickel is the most commonly used standard sample. It
5. Test Specimen
can be obtained in high purity, resists oxidation and corrosion,
5.1 The test specimen shall preferably be in the form of an
and has a saturation magnetization lower than that of iron and
isotropic sphere. The size of the sphere will depend on the
cobalt but higher than that of ferrites. The saturation magneti-
measuring apparatus to be used, but for the usual instrument
zation of nickel at 20°C and 10-kOe [800-kA/m] applied field
3 3
thesizewillbe0.5cm[5mm]orlessindiameter.Methodsfor
maybetaken (10)as492 62emu/cm [(492 62)×10 A/m].
producing small spherical samples are given in Refs (5-8).
The temperature coefficient of magnetization is−0.05% per
5.1.1 Forthesampletobeisotropic,thecrystalsizeorgrain
°C, and the field coefficient is about+0.2% per kOe from 5 to
size of the sample material must be small compared to the
15 kOe [+2.5% per MA/m from 0.4 to 1.2 MA/m].
sample size. Furthermore, the crystals should be of random
6.2 Moment from Coil—The standard sample may be re-
orientation. If the sample is not isotropic, it is still possible to
placed by a coil of known dimensions and number of turns
measure the saturation magnetization, but the field required to
carrying a known dc current. Such a coil produces a dipole
reach saturation will depend on the direction in which the field
field the same as that produced by a spherical sample. The
is applied to the sample, and there will in general be a torque
magnitude of the equivalent moment is given by:
acting on the sample which may be large enough to interfere
2 2 2
with the measurement.
m 5 πr ni/10 emu or m 5 πr ni @A·m #
~ !
5.1.2 The same measuring technique can be applied to
where:
highly anisotropic samples such a
...
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