FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
VIBRATING SAMPLE MAGNETOMETER;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
TITLE OF THE INVENTION:
VIBRATING SAMPLE MAGNETOMETER
5
Field
[0001] The present disclosure relates to a vibrating
sample magnetometer.
10 Background
[0002] A vibrating sample magnetometer vibrates a
magnetic sample placed in a magnetic field at a constant
frequency and a constant amplitude, and measures
electromotive force induced in detection coils disposed
15 around the magnetic sample. Thus, the vibrating sample
magnetometer derives magnetic properties of the magnetic
sample based on a relational expression between
electromotive force and magnetic properties. Magnetic
properties of a magnetic sample deteriorate when an
20 external load is applied. Therefore, for a magnetic sample
that operates under pressure, it is necessary to measure
magnetic properties of the magnetic sample being subjected
to external force.
[0003] Patent Literature 1 discloses a vibrating sample
25 magnetometer that includes a means for applying pressure to
a measurement sample and a pressure measurement means for
measuring the applied pressure. The vibrating sample
magnetometer is configured such that the measurement sample
can be vibrated while being subjected to pressure.
30
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent Application
3
Laid-open No. 2018-84463
Summary of Invention
Problem to be solved by the Invention
5 [0005] When a strong magnetic field is externally
applied to a magnetic sample being subjected to external
pressure, deteriorated magnetic properties are slightly
restored. The technique disclosed in Patent Literature 1
allows measurement of magnetic properties of a measurement
10 sample being subjected to external stress. However, the
magnetic properties are restored due to a strong magnetic
field applied externally to the measurement sample when the
magnetic field is swept. Therefore, there is a problem in
that deterioration of magnetic properties due to
15 application of external stress cannot be accurately
measured.
[0006] The present disclosure has been made in view of
the above, and an object of the present disclosure is to
obtain a vibrating sample magnetometer capable of
20 accurately measuring deterioration of magnetic properties
due to external pressure applied to a measurement sample.
Means to Solve the Problem
[0007] In order to solve the above-described problem and
25 achieve the object, a vibrating sample magnetometer of the
present disclosure includes: a sample housing vibrating
body that houses a measurement sample, and vibrates the
measurement sample in a single direction; an excitation
electromagnet that applies an external magnetic field to
30 the measurement sample; a pressure application unit that
applies pressure to the measurement sample; a pressure
acquisition unit that measures the applied pressure; a
magnetic property acquisition unit that detects an induced
4
voltage caused by vibration of the measurement sample
magnetized by the excitation electromagnet and acquires a
magnetic property, the magnetic property indicating a
relationship between a magnetic flux density and the
5 external magnetic field, the magnetic flux density being a
sum of magnetization of the measurement sample and the
external magnetic field; and a control device that controls
the external magnetic field and the pressure, and sweeps
the external magnetic field. When acquiring the magnetic
10 property of the measurement sample to which the pressure is
being applied, the control device sets a first magnetic
field value as a sweep start value, and sweeps the external
magnetic field with a magnetic field equal to or less than
the first magnetic field value. The first magnetic field
15 value is smaller than a second magnetic field value
acquired before the pressure is applied to the measurement
sample, the second magnetic field value being a magnetic
field value corresponding to a saturation magnetic flux
density of the measurement sample to which the pressure is
20 not being applied.
Effects of the Invention
[0008] The vibrating sample magnetometer of the present
disclosure has the effect of enabling accurate measurement
25 of deterioration of magnetic properties due to external
pressure applied to a measurement sample.
Brief Description of Drawings
[0009] FIG. 1 is a diagram showing a schematic
30 configuration example of a vibrating sample magnetometer
according to a first embodiment.
FIG. 2 is a block diagram showing a functional
configuration example of a control device of the vibrating
5
sample magnetometer according to the first embodiment.
FIG. 3 is a block diagram showing an example of a
hardware configuration of the control device of the
vibrating sample magnetometer according to the first
5 embodiment.
FIG. 4 is a process chart showing an example of a
measurement procedure of the vibrating sample magnetometer
according to the first embodiment.
FIG. 5 is a diagram illustrating magnetic properties
10 obtained under a first measurement condition in an unloaded
state in the first embodiment.
FIG. 6 is a diagram illustrating magnetic properties
obtained under a second measurement condition in a loaded
state in the first embodiment.
15 FIG. 7 is a diagram illustrating magnetic properties
obtained when a measurement sample is unloaded after being
subjected to a load in the first embodiment.
FIG. 8 is a process chart showing an example of a
measurement procedure of a vibrating sample magnetometer
20 according to a second embodiment.
FIG. 9 is a diagram illustrating magnetic properties
obtained under the second measurement condition
corresponding to a loaded state in the second embodiment.
FIG. 10 is a process chart showing an example of a
25 measurement procedure of a vibrating sample magnetometer
according to a third embodiment.
FIG. 11 is a diagram illustrating magnetic properties
obtained under the second measurement condition in a loaded
state in the third embodiment.
30
Description of Embodiments
[0010] Hereinafter, a vibrating sample magnetometer
according to each embodiment will be described in detail
6
with reference to the drawings.
[0011] First Embodiment.
FIG. 1 is a diagram showing a schematic configuration
example of a vibrating sample magnetometer 100 according to
5 a first embodiment. The vibrating sample magnetometer 100
includes a sample housing vibrating body 1, a support
platform 2, a vibrating device 3, an external force
application mechanism 4, a magnetic property imparting and
measuring unit 5, a temperature control gas supply pipe 7,
10 a temperature control gas supply device 8, and a control
device 10.
[0012] The sample housing vibrating body 1 vibrates in a
single direction. In this case, the sample housing
vibrating body 1 vibrates up and down. The sample housing
15 vibrating body 1 includes a sample storage portion 1a and a
pressure application rod 1b. The sample storage portion 1a
is hollow and cylindrical, and houses a measurement sample
S. The pressure application rod 1b is inserted into the
sample storage portion 1a, and applies pressure to the
20 measurement sample S. The sample housing vibrating body 1
includes a temperature detection unit 1c that detects the
temperature of the measurement sample S. The temperature
of the measurement sample S detected by the temperature
detection unit 1c is input to the control device 10. In
25 addition, the sample housing vibrating body 1 includes a
vibration detection unit (not illustrated) that detects a
vibration state including the frequency and amplitude of
vibration of the sample housing vibrating body 1. The
vibration state of the sample housing vibrating body 1
30 detected by the vibration detection unit is input to the
control device 10.
[0013] The vibrating device 3 vibrates the sample
housing vibrating body 1 up and down. The support platform
7
2 is a platform for securing the vibrating device 3. The
vibrating device 3 vibrates the sample housing vibrating
body 1 up and down based on a vibration frequency and an
amplitude specified by the control device 10.
5 [0014] The external force application mechanism 4 is
connected to the pressure application rod 1b of the sample
housing vibrating body 1, and applies external force to the
measurement sample S by applying the external force to the
pressure application rod 1b. The external force
10 application mechanism 4 includes a pressure detection unit
4a. The pressure detection unit 4a is, for example, a load
cell. The load cell converts force into an electrical
signal by using a strain gauge. The pressure detection
unit 4a detects a pressure applied to the measurement
15 sample S by measuring a pressure received by the pressure
application rod 1b from the measurement sample S. The
pressure applied to the measurement sample S and detected
by the pressure detection unit 4a is input to the control
device 10.
20 [0015] The magnetic property imparting and measuring
unit 5 includes an excitation electromagnet 5a and a
detection coil 5b. The excitation electromagnet 5a applies
an external magnetic field to the measurement sample S.
The detection coil 5b detects an induced voltage caused by
25 vibration of the measurement sample S magnetized by the
excitation electromagnet 5a. The detection coil 5b is
disposed in the vicinity of the measurement sample S. The
induced voltage detected by the detection coil 5b is input
to the control device 10.
30 [0016] The temperature control gas supply device 8
supplies a temperature control gas for controlling the
temperature of the measurement sample S to the periphery of
the measurement sample S housed in the sample housing
8
vibrating body 1, via the temperature control gas supply
pipe 7. It is possible to heat or cool the measurement
sample S by blowing the temperature control gas onto the
measurement sample S. The temperature of the temperature
5 control gas is controlled by the control device 10.
[0017] In such a configuration, the measurement sample S
is disposed at a tip of the sample storage portion 1a of
the sample housing vibrating body 1. The temperature of
the measurement sample S is detected by the temperature
10 detection unit 1c of the sample housing vibrating body 1.
The temperature of the measurement sample S is adjusted by
the temperature control gas supplied from the temperature
control gas supply device 8. The pressure application rod
1b is inserted into the sample storage portion 1a, and the
15 measurement sample S is secured to the sample storage
portion 1a by the pressure application rod 1b. In this
state, the sample housing vibrating body 1 is vibrated in a
vertical direction by the vibrating device 3. This
vibration state is detected by the vibration detection unit
20 (not illustrated). Pressure is applied to the measurement
sample S in the same direction as a direction of the
vibration, by means of the external force application
mechanism 4 and the pressure application rod 1b. When the
pressure acts on the measurement sample S, a force in an
25 opposite direction acts on the pressure application rod 1b
as a reaction. Pressure acting on the pressure application
rod 1b is detected by the pressure detection unit 4a of the
external force application mechanism 4. An induced voltage
is caused from vibration in the measurement sample S. This
30 induced voltage is detected by the detection coil 5b of the
magnetic property imparting and measuring unit 5. In
addition, the measurement sample S is magnetized by an
external magnetic field applied with the excitation
9
electromagnet 5a.
[0018] The control device 10 controls the vibrating
device 3, the external force application mechanism 4, the
magnetic property imparting and measuring unit 5, and the
5 temperature control gas supply device 8. FIG. 2 is a block
diagram showing a functional configuration example of the
control device 10 of the vibrating sample magnetometer 100
according to the first embodiment. The control device 10
includes a main control unit 11, a magnetic property
10 acquisition unit 12, a temperature acquisition unit 13, a
pressure acquisition unit 14, a vibration control unit 15,
a temperature control unit 16, a pressure control unit 17,
an external load environment determination unit 18, and an
external magnetic field sweep unit 19.
15 [0019] On the basis of a result of measuring
magnetization of the measurement sample S obtained from the
detection coil 5b, the magnetic property acquisition unit
12 calculates a magnetic property indicating a
correspondence relationship between a magnetic flux density
20 B, which is a sum of the magnetization of the measurement
sample S and an external magnetic field, and an external
magnetic field (magnetic field) H. The magnetic property
acquisition unit 12 sends the calculated magnetic property
to the main control unit 11.
25 [0020] The temperature acquisition unit 13 calculates a
temperature T of the measurement sample S based on a result
of detection of the temperature of the measurement sample S
obtained from the temperature detection unit 1c, and sends
the calculated temperature T to the main control unit 11.
30 [0021] The pressure acquisition unit 14 calculates an
external pressure (pressure) P applied to the measurement
sample S based on a pressure detection result regarding the
pressure of the measurement sample S detected by the
10
pressure detection unit 4a, and sends the calculated
external pressure P to the main control unit 11.
[0022] The vibration control unit 15 controls the
vibrating device 3. The vibration control unit 15 controls
5 the vibrating device 3 by providing feedback on a vibration
state of the sample housing vibrating body 1 acquired from
the vibration detection unit (not illustrated), to control
the vibration frequency, amplitude, vibration start time,
and vibration end time of vertical vibration of the sample
10 housing vibrating body 1.
[0023] The temperature control unit 16 acquires, from
the main control unit 11, the temperature T of the
measurement sample S calculated by the temperature
acquisition unit 13. The temperature control unit 16
15 controls the temperature control gas supply device 8 by
providing feedback on the temperature T of the measurement
sample S, to control the temperature of the temperature
control gas to be supplied from the temperature control gas
supply device 8.
20 [0024] The pressure control unit 17 acquires, from the
main control unit 11, the pressure P applied to the
measurement sample S calculated by the pressure acquisition
unit 14. The pressure control unit 17 controls the
external force application mechanism 4 by providing
25 feedback on the pressure P applied to the measurement
sample S, to control the pressure application rod 1b such
that the specified pressure P is applied to the measurement
sample S.
[0025] The external load environment determination unit
30 18 derives a sweep start value Hs and a sweep end value He
of the external magnetic field H, on the basis of a result
of measurement of the magnetic property indicating the
correspondence relationship between the magnetic flux
11
density B and the external magnetic field H, and the
external load environment determination unit 18 transmits
the derived values to the main control unit 11.
[0026] The external magnetic field sweep unit 19
5 acquires, from the main control unit 11, the sweep start
value Hs and the sweep end value He of the external
magnetic field H. The external magnetic field sweep unit
19 transmits the sweep start value Hs and the sweep end
value He of the external magnetic field H to the excitation
10 electromagnet 5a, and performs sweep control for the
excitation electromagnet 5a.
[0027] The main control unit 11 controls each of
functional units including the magnetic property
acquisition unit 12, the temperature acquisition unit 13,
15 the pressure acquisition unit 14, the vibration control
unit 15, the temperature control unit 16, the pressure
control unit 17, the external load environment
determination unit 18, and the external magnetic field
sweep unit 19, by transmitting control signals to the
20 functional units on the basis of information acquired from
the functional units.
[0028] FIG. 3 is a block diagram showing an example of a
hardware configuration of the control device 10 of the
vibrating sample magnetometer 100 according to the first
25 embodiment. The control device 10 can be implemented by a
processor 101, a memory 102, and an interface circuit 103
illustrated in FIG. 3. Examples of the processor 101
include a central processing unit (CPU) (also referred to
as a processing device, an arithmetic device, a
30 microprocessor, a microcomputer, or a digital signal
processor (DSP)) and a system large-scale integration
(LSI). Examples of the memory 102 include a random access
memory (RAM) and a read only memory (ROM).
12
[0029] The control device 10 is implemented by the
processor 101 reading and executing a program for executing
the operation of the control device 10, stored in the
memory 102. It can also be said that this program causes a
5 computer to execute a procedure or a method of the control
device 10. The memory 102 is also used as a temporary
memory when the processor 101 executes various types of
processing. Note that some of the functions of the control
device 10 may be implemented by dedicated hardware, and
10 some of the other functions thereof may be implemented by
software or firmware.
[0030] It is known that when pressure is applied
externally to the measurement sample S that is a magnetic
material, magnetic properties are deteriorated. Meanwhile,
15 the present inventors have newly found that when pressure
(stress) is applied externally to the measurement sample S
and a strong magnetic field is then applied externally to
the measurement sample S when magnetic properties have been
deteriorated, the deteriorated magnetic properties are
20 partially or completely restored. Thus, when an external
magnetic field that is too strong is applied to the
measurement sample S to which pressure is being applied
externally, the deteriorated magnetic properties are
partially or completely restored.
25 [0031] When measuring magnetic properties of the
measurement sample S to which pressure is being applied,
the vibrating sample magnetometer of Patent Literature 1
acquires magnetic properties while sweeping an external
magnetic field to a strong magnetic field side, and then
30 sweeping the external magnetic field to a low magnetic
field side while the pressure is being applied to the
measurement sample S. However, in this method, magnetic
properties deteriorated by pressure applied externally to
13
the measurement sample S cannot be accurately acquired, and
instead, magnetic properties are acquired after partial or
complete restoration of the magnetic properties
deteriorated by the applied pressure.
5 [0032] In a product including magnetic material, such as
a motor device, magnetic properties are deteriorated under
the influence of stress due to centrifugal force that is
caused by rotation of a motor. However, general motor
devices have no mechanism for restoring deteriorated
10 magnetic properties. Therefore, if it is not possible to
accurately grasp the magnetic properties of the magnetic
material deteriorated only by the influence of stress, the
motor performance of a motor device being used cannot be
accurately evaluated.
15 [0033] Thus, in order to accurately grasp the state of
deterioration of magnetic properties due to the influence
of stress, the vibrating sample magnetometer 100 of the
first embodiment specifies, as the sweep start value Hs, a
magnetic field that is sufficiently weak to avoid restoring
20 the magnetic properties deteriorated by externally applied
pressure. Them, the vibrating sample magnetometer 100
applies, to the measurement sample S, a magnetic field
equal to or less than the specified sweep start value Hs to
sweep the magnetic field.
25 [0034] In order to accurately grasp the state of
deterioration of magnetic properties due to the influence
of pressure, the vibrating sample magnetometer 100 of the
first embodiment performs, for example, the following
measurement. FIG. 4 is a process chart showing an example
30 of a measurement procedure of the vibrating sample
magnetometer 100 according to the first embodiment.
[0035] First, the vibration control unit 15 controls the
vibrating device 3, and specifies a vibration frequency and
14
an amplitude such that the sample housing vibrating body 1
vibrates up and down at the specified vibration frequency
and amplitude. The temperature control unit 16 controls
the temperature control gas supply device 8 such that the
5 temperature T of the measurement sample S becomes T0. The
temperature “T0” is, for example, 25°C. The pressure
control unit 17 controls the external force application
mechanism 4 such that the pressure P to be applied to the
measurement sample S becomes a pressure (pressure P=P0=0
10 MPa) in an unloaded state. As above, the control device 10
sets a measurement condition of the measurement sample S to
a first measurement condition (P0,T0) that is in the
unloaded state. Thereafter, the external magnetic field
sweep unit 19 performs full-loop magnetic-field sweep
15 control of controlling the excitation electromagnet 5a to
apply the external magnetic field (magnetic field) H to the
measurement sample S in an initial state. The magnetic
property acquisition unit 12 acquires full-loop magnetic
properties of the measurement sample S generated by the
20 magnetic-field sweep control, based on a measurement result
of magnetization of the measurement sample S obtained from
the detection coil 5b (step S100). The measurement sample
in the initial state refers to a measurement sample to
which no load has been applied before.
25 [0036] FIG. 5 is a diagram illustrating magnetic
properties (B-H loop) obtained under the first measurement
condition (P0,T0) in the unloaded state in the first
embodiment. In FIG. 5, the vertical axis represents the
magnetic flux density B (unit: tesla), and the horizontal
30 axis represents the magnetic field H (unit: A/m). The
magnetic properties under this measurement condition are
values generally shown in a catalog of magnetic materials.
[0037] Full-loop magnetic-field sweep control is
15
performed under the first measurement condition (P0,T0) as
follows. First, the external magnetic field H is applied
to the measurement sample S that is in the initial state
such that the external magnetic field H increases from zero
5 (H=0) to Hlmt. The value Hlmt is a positive-side limit
value of the excitation electromagnet 5a and the detection
coil 5b of the magnetic property imparting and measuring
unit 5, which is a measuring instrument. As a result, the
measurement sample S is magnetized, and the magnetic flux
10 density B increases along a line L1 from the origin O,
where B=0, to a point C1 having a saturation magnetic flux
density Bs. The magnetic field H corresponding to the
saturation magnetic flux density Bs is also referred to as
a maximum magnetization force Hmax. The maximum
15 magnetization force Hmax of the magnetic properties
obtained under the first measurement condition (P0,T0) that
is in the unloaded state, corresponds to a second magnetic
field value in the claims.
[0038] Next, the external magnetic field H is applied to
20 the measurement sample S such that the external magnetic
field H decreases from the positive-side limit value “Hlmt”
to zero (H=0). As a result, the measurement sample S is
demagnetized, and the magnetic flux density B decreases
along a line L2 from the point C1, where B=Bs, to a
25 residual magnetic flux density Br.
[0039] Next, the external magnetic field H is applied to
the measurement sample S in a reverse direction such that
the external magnetic field H increases from zero (H=0) to
a negative-side limit value “-Hlmt” of the measuring
30 instrument. As a result, the magnetic flux density B
increases along a line L3 from the residual magnetic flux
density Br to a point C2 having a saturation magnetic flux
density “-Bs” via a holding force HCB where B=0. The symbol
16
“BHmax” represents a point indicating a maximum energy
product that is a maximum value of the product of the
magnetic flux density B and the magnetic field H on a
demagnetization curve.
5 [0040] Next, the external magnetic field H is applied to
the measurement sample S such that the external magnetic
field H decreases from the negative-side limit value “-
Hlmt” to zero (H=0). As a result, the measurement sample S
is demagnetized, and the magnetic flux density B decreases
10 along a line L4 from the point C2, where B=-Bs, to a
residual magnetic flux density “-Br”.
[0041] Next, the external magnetic field H is applied to
the measurement sample S in a reverse direction such that
the external magnetic field H increases from zero (H=0) to
15 the positive-side limit value “Hlmt” of the measuring
instrument. As a result, the magnetic flux density B
increases along a line L5 from the residual magnetic flux
density “-Br” to the point C1 having the saturation
magnetic flux density “Bs” via the holding force “HCB”
20 where B=0.
[0042] FIG. 6 is a diagram illustrating magnetic
properties (B-H loop) obtained under a second measurement
condition (P1,T0) in a loaded state in the first
embodiment. A broken line L2 in FIG. 6 corresponds to the
25 line L2 of the unloaded state in FIG. 5. Next, the control
device 10 controls the temperature control gas supply
device 8, the external force application mechanism 4, and
the magnetic property imparting and measuring unit 5 to
apply the external magnetic field H to the measurement
30 sample S such that the external magnetic field H changes
from zero (H=0) to the positive-side limit value “Hlmt” of
the measuring instrument, while keeping the measurement
condition of the measurement sample S to the first
17
measurement condition (P0,T0) that is in the unloaded
state. As a result, magnetic properties are acquired as
indicated by a line Q1 in FIG. 6.
[0043] Next, the control device 10 sets the measurement
5 condition of the measurement sample S to the second
measurement condition (P1,T0) that is in the loaded state.
For example, the pressure P1=100 MPa, and the temperature
T0=25°C. In addition, the external load environment
determination unit 18 of the control device 10 sets the
10 sweep start value Hs of the external magnetic field H to
zero (H=0), and sets the sweep end value He of the external
magnetic field H to the negative-side limit value “-Hlmt”
described above. Then, the control device 10 executes
sweep control after the temperature T and the pressure P of
15 the measurement sample S are stabilized. As a result,
sweep control for the external magnetic field H is
performed when an external load is applied to the
measurement sample S. According to the magnetic-field
sweep control with the external magnetic field H changing
20 from zero (H=0) to the negative-side limit value “-Hlmt”
under the second measurement condition (P1,T0), a portion
of the magnetic properties in the first quadrant is skipped
as indicated by an arrow 30 in FIG. 6. Furthermore, a
demagnetization curve corresponding to magnetic properties
25 in the second quadrant and the third quadrant are acquired
as indicated by a line Q2 (step S110).
[0044] When the magnetic properties are acquired in the
loaded state under the second measurement condition
(P1,T0), it is necessary to set, as the sweep start value
30 Hs, an external magnetic field that is sufficiently weak to
prevent magnetic properties from being restored. A maximum
value of the external magnetic field that is sufficiently
weak to prevent magnetic properties from being restored has
18
not yet been determined under the second measurement
condition (P1,T0). Thus, a simplest method is adopted in
which the sweep start value Hs is set to zero (H=0).
Therefore, an external magnetic field larger than zero
5 (H=0) may be set as the sweep start value Hs as long as the
external magnetic field is sufficiently weak to prevent
magnetic properties from being restored.
[0045] Next, the external load environment determination
unit 18 of the control device 10 calculates a difference
10 ΔB1 between the magnetic properties under the first
measurement condition (P0,T0) and the magnetic properties
under the second measurement condition (P1,T0) (step S120).
The demagnetization properties of the measurement sample S
to which pressure (stress) is being applied can be grasped
15 from the difference ΔB1.
[0046] FIG. 7 is a diagram illustrating magnetic
properties obtained when the measurement sample S is
unloaded after being subjected to a load in the first
embodiment. A broken line L2 in FIG. 7 corresponds to the
20 line L2 in FIG. 5. After acquiring the magnetic properties
under the second measurement condition (P1,T0), the control
device 10 sets again the measurement condition of the
measurement sample S to a third measurement condition
(P0',T0) that is in the unloaded state. For example, it is
25 set that the pressure P0=0 MPa, and the temperature
T0=25°C. The third measurement condition and the first
measurement condition are identical in pressure P and
temperature T. However, the third measurement condition is
different from the first measurement condition in that the
30 measurement sample S is unloaded after being subjected to a
load. Therefore, the measurement condition concerned is
referred to as the third measurement condition, and
pressure is represented as P=P0'. In addition, as
19
described with reference to FIG. 5, the control device 10
performs full-loop magnetic-field sweep control of
controlling the excitation electromagnet 5a to apply the
external magnetic field H to the measurement sample S (step
5 S130). That is, the external magnetic field is swept from
zero (H=0) to the positive-side limit value “Hlmt”, swept
from the positive-side limit value “Hlmt” to the negativeside limit value “-Hlmt”, and swept from the negative-side
limit value “-Hlmt” to the positive-side limit value
10 “Hlmt”. According to the magnetic-field sweep control
performed again under the third measurement condition
(P0',T0), it is possible to acquire the full-loop B-H loop
regarding the measurement sample S from which stress has
been unloaded, as illustrated in FIG. 7.
15 [0047] Here, the holding force of a magnet is
considered. A large number of crystal grains are included
in a magnet, and each crystal grain has a magnetic domain
structure. A neodymium magnet is produced by the
compression molding and sintering of magnet powder, but
20 does not have holding force immediately after production,
so that magnetic properties are not exhibited. When a
magnetic field is applied to a magnet from an external coil
or the like, the magnetic domain orientations of crystal
grains are aligned in a single direction, so that magnetic
25 properties are exhibited. Thus, what is called a magnet is
obtained. Since magnetic properties correspond to the sum
of magnetic domain structures of crystal grains, the more
crystal grains with magnetic domain structures aligned in a
single direction are present, the higher the magnetic
30 properties are.
[0048] Incidentally, it is conceivable that weakened
magnetic properties of a magnet, that is, demagnetization
will be caused by a shift from a configuration in which the
20
magnetic domain orientations of crystal grains are aligned
in a single direction to a configuration in which the
magnetic domain orientations of some of the crystal grains
are not aligned, or a configuration in which a magnetic
5 domain itself has changed to a plurality of magnetic
domains (multi-domain structure). In order to align, in a
single direction, the magnetic domains of the crystal
grains of the magnet oriented in various directions, it is
necessary to externally apply a magnetic field to the
10 magnet by means of an external coil or the like. When a
magnetic field is applied externally to the magnet, there
is a possibility that crystal grains having magnetic
domains oriented in various directions or crystal grains
with a multi-domain structure can be reproduced as crystal
15 grains with a single-domain structure in which magnetic
domains are oriented in a single direction (reversible
demagnetization). Meanwhile, there are also crystal grains
with a magnetic domain structure that cannot be changed
into a single-domain structure (irreversible
20 demagnetization), such as crystal grains having magnetic
domains oriented in different directions due to an external
load, such as stress, or crystal grains with a multi-domain
structure in which magnetic domains are oriented in various
directions.
25 [0049] Here, considered is demagnetization of the
magnetic properties of the measurement sample S to which
pressure is applied. As described above, magnet
demagnetization includes reversible demagnetization and
irreversible demagnetization. In the reversible
30 demagnetization, when a magnetic field is applied
externally to the measurement sample S again, magnetic
domain structures are aligned, and magnetic properties are
reproduced. That is, in the reversible demagnetization,
21
magnetic properties are restored from a demagnetized state.
Meanwhile, in the irreversible demagnetization, even when a
magnetic field is applied externally to the measurement
sample S again, the magnetic domain structures are not
5 aligned, and magnetic properties are not reproduced. That
is, in the irreversible demagnetization, magnetic
properties are not restored from the demagnetized state.
Demagnetization of the magnetic properties of the
measurement sample S to which stress is applied includes
10 reversible demagnetization and irreversible
demagnetization.
[0050] The external load environment determination unit
18 of the control device 10 calculates a difference ΔB2
between magnetic properties under the first measurement
15 condition (P0,T0) and magnetic properties under the third
measurement condition (P0',T0) (step S140). As a result,
it is possible to detect the difference ΔB2 between the
magnetic properties of the measurement sample S before and
after being subjected to pressure. Here, if the difference
20 ΔB2 occurs, it can be confirmed that the change in magnetic
property due to the pressure applied to the measurement
sample S is an irreversible change.
[0051] In addition, the external load environment
determination unit 18 of the control device 10 acquires the
25 saturation magnetic flux density Bs (see FIG. 7) of the
magnetic properties under the third measurement condition
(P0',T0), and further acquires a magnetic field value H1
(see FIG. 7) corresponding to the saturation magnetic flux
density Bs. Furthermore, the external load environment
30 determination unit 18 of the control device 10 selects, as
a first magnetic field value Ha, any magnetic field value
from among values of the external magnetic field H
satisfying H≤H1. Then, the external load environment
22
determination unit 18 specifies the selected first magnetic
field value Ha as the sweep start value Hs for acquiring
magnetic properties in the loaded state (step S150). That
is, the external load environment determination unit 18 of
5 the control device 10 sets, as the sweep start value Hs,
the first magnetic field value Ha. The value Ha is a
magnetic field value equal to or less than the magnetic
field value H1, which corresponds to the saturation
magnetic flux density Bs in the magnetic properties in the
10 unloaded state.
[0052] In this way, when the first magnetic field value
Ha is specified as the sweep start value Hs for acquiring
magnetic properties in the loaded state, the control device
10 performs magnetic field sweep by using the specified
15 sweep start value Hs (=Ha) to acquire the magnetic
properties of the measurement sample S in the loaded state
(step S160). In the example of FIG. 6, the sweep start
value Hs is set to zero (H=0). Here, the sweep start value
Hs is set such that H=Ha, and the magnetic properties in
20 the loaded state are acquired similarly to FIG. 6. As a
result, if the first magnetic field value Ha is set to a
value that allows acquisition of magnetic properties in the
first quadrant, the magnetic properties in the first
quadrant can also be acquired. In addition, when magnetic
25 properties in the loaded state returning from the third
quadrant to the first quadrant via the fourth quadrant are
acquired, the value H just needs to be set as the sweep end
value He such that H=Ha. Furthermore, when magnetic
properties of another measurement sample S made of the same
30 material, including magnetic properties in the first
quadrant, are acquired thereafter, the sweep start value Hs
in step S110 may be set such that H=Ha. Then, the
processing of steps S130 to S160 may be omitted so that the
23
procedure is terminated in step S120.
[0053] As described above, in the first embodiment,
after the pressure P is applied to the measurement sample
S, the applied pressure P is unloaded from the measurement
5 sample S, and magnetic properties of the measurement sample
S from which the pressure P has been unloaded are acquired.
Furthermore, the sweep start value Hs is set as the first
magnetic field value Ha that is equal to or less than the
magnetic field value H1, which corresponds to the
10 saturation magnetic flux density Bs in the magnetic
properties of the measurement sample S from which the
pressure P has been unloaded. Then, the magnetic
properties (B-H characteristics) of the measurement sample
S starting from the sweep start value Hs are acquired.
15 Therefore, a strong magnetic field is not applied
externally to the measurement sample S at the time of
magnetic field sweep. As a result, it is possible to
accurately measure deterioration of the magnetic properties
due to application of the external stress. This makes it
20 possible to accurately estimate the deterioration state of
the magnetic properties of magnetic material included in a
motor device or the like.
[0054] Second Embodiment.
Here, a demagnetizing field of the measurement sample
25 S is considered. A magnetized magnetic body also generates
a magnetic field inside the magnetic body. A magnet has
two magnetic poles including the N-pole and the S-pole, and
magnetic flux goes out of the magnet from the N-pole and
returns to the S-pole. However, separately from the
30 magnetic flux leaking to the outside, magnetic flux flowing
from the N-pole to the S-pole exists inside the magnet.
The direction of the magnetic flux inside the magnet is
opposite to the direction of the magnetic flux returning
24
from the outside of the magnet. Therefore, such a magnetic
field is referred to as a demagnetizing field.
[0055] In order to accurately evaluate magnetic
properties of the measurement sample S, it is necessary to
5 express the magnetic properties with a B-H loop from which
the influence of the demagnetizing field is removed.
However, in a vibrating sample magnetic force measuring
apparatus that measures an open magnetic circuit, it is
necessary to make correction for the influence of the
10 demagnetizing field. Otherwise, unlike a B-H loop measured
in a closed magnetic circuit that is not affected by the
demagnetizing field, magnetic properties are not accurately
evaluated.
[0056] In the measurement of an open magnetic circuit,
15 there is a demagnetizing field correction technique as a
method of creating a B-H loop from which the influence of
the demagnetizing field is removed. The demagnetizing
field correction technique is a technique for correcting a
distorted B-H loop measured in an open magnetic circuit to
20 a loop having a shape similar to that of a B-H loop
measured in a closed magnetic circuit. There are various
methods known as the demagnetizing field correction
technique.
[0057] As one of demagnetizing field correction methods,
25 there is a method of performing algorithm calculation for
predicting a B-H loop of closed magnetic circuit
measurement from a B-H loop of open magnetic circuit
measurement. When such a correction method is applied, it
is possible to increase the prediction accuracy of the B-H
30 loop of closed magnetic circuit measurement, as the number
of measurement points of B-H characteristics in the first
quadrant of a B-H loop increases.
[0058] Therefore, in order to increase the number of
25
measurement points of the B-H characteristics in the first
quadrant, measurement is performed in a second embodiment
as follows. FIG. 8 is a process chart showing an example
of a measurement procedure of a vibrating sample
5 magnetometer according to a second embodiment. FIG. 9 is a
diagram illustrating magnetic properties (B-H loop)
obtained under the second measurement condition (P1,T0)
corresponding to a loaded state in the second embodiment.
The measurement procedure of the second embodiment will be
10 described below with reference to FIGS. 5, 8, and 9.
[0059] First, as described with reference to FIG. 5, the
control device 10 sets the measurement condition of the
measurement sample S in the initial state to the first
measurement condition (P0,T0) described above that is in
15 the unloaded state. The pressure P0=0 MPa, and the
temperature T0=25°C. In addition, the control device 10
performs full-loop magnetic-field sweep control of
controlling the excitation electromagnet 5a to apply the
external magnetic field H to the measurement sample S.
20 That is, the external magnetic field is swept from zero
(H=0) to the positive-side limit value “Hlmt”, swept from
the positive-side limit value “Hlmt” to the negative-side
limit value “-Hlmt”, and swept from the negative-side limit
value “-Hlmt” to the positive-side limit value “Hlmt”.
25 According to the magnetic-field sweep control under the
first measurement condition (P0,T0), a full-loop B-H loop
can be acquired as illustrated in FIG. 5 (step S200).
[0060] Next, the control device 10 controls the
temperature control gas supply device 8, the external force
30 application mechanism 4, and the magnetic property
imparting and measuring unit 5 to apply the external
magnetic field H to the measurement sample S such that the
external magnetic field H changes from zero (H=0) to the
26
positive-side limit value “Hlmt” of the measuring
instrument, while keeping the measurement condition of the
measurement sample S to the first measurement condition
(P0,T0) that is in the unloaded state. As a result,
5 magnetic properties are acquired as indicated by a line G1
in FIG. 9.
[0061] Next, the control device 10 reduces the external
magnetic field H to a magnetic field value H2 which is the
sweep start value Hs. As indicated by an arrow 31 in FIG.
10 9, a value selected as the magnetic field value H2 is
smaller than the maximum magnetization force Hmax of the
previously measured magnetic properties illustrated in FIG.
5 under the first measurement condition (P0,T0) that is in
the unloaded state. The maximum magnetization force Hmax
15 is a value of the magnetic field H corresponding to the
saturation magnetic flux density (maximum magnetic flux
density) Bs. Here, a value that is 5% lower than the
maximum magnetization force Hmax is selected as the
magnetic field value H2. In addition, the control device
20 10 sets the sweep end value He of the external magnetic
field to the negative-side limit value “-Hlmt”.
[0062] Next, the control device 10 sets the measurement
condition of the measurement sample S to the second
measurement condition (P1,T0) that is in the loaded state.
25 For example, the pressure P1=100 MPa, and the temperature
T0=25°C. After the temperature and pressure of the
measurement sample S are stabilized, the control device 10
executes magnetic-field sweep control with the external
magnetic field H changing from the magnetic field value H2
30 to the sweep end value “-Hlmt” in the loaded state. As a
result, while an external load is being applied to the
measurement sample S, the magnetic-field sweep control is
executed with the external magnetic field H changing from
27
the magnetic field value H2 to the sweep end value “-Hlmt”.
According to the magnetic-field sweep control with the
external magnetic field H changing from H2 (H=H2) to the
negative-side limit value “-Hlmt” under the second
5 measurement condition (P1,T0), a demagnetization curve as
magnetic properties in the first quadrant is acquired as
indicated by a line G2 in FIG. 9, and a demagnetization
curve as magnetic properties in the second quadrant and the
third quadrant is acquired as indicated by a line G3 (step
10 S210).
[0063] Next, the control device 10 calculates a
difference ΔB3 between the magnetic properties under the
first measurement condition (P0,T0) and the magnetic
properties under the second measurement condition (P1,T0)
15 (step S220). The demagnetization properties of the
measurement sample S to which stress is being applied can
be grasped based on the difference ΔB3.
[0064] Here, it is desirable to select, as the magnetic
field value H2, different values depending on resistance to
20 demagnetization of the measurement sample S regarding the
external load. For example, when the demagnetization
resistance of the measurement sample S is low, and a
maximum magnetic field force Hmax1 indicated by the B-H
characteristics under conditions of P1=100 MPa and T0=25°C
25 is demagnetized by 7% as compared with the maximum
magnetization force Hmax in the unloaded state, a value of,
for example, 10% that is lower by 7% or more than the
maximum magnetization force Hmax is selected as the
magnetic field value H2. As illustrated in FIG. 9, the
30 maximum magnetic field force Hmax1 is acquired from the
demagnetization curve in the third quadrant. This is
because, if a value is selected as the magnetic field value
H2 such that H2>Hmax1, there is a possibility that the
28
magnetic properties of the measurement sample S may be
restored, which may result in that demagnetization
properties due to an external load cannot be accurately
evaluated.
5 [0065] In order to increase the number of measurement
points of B-H characteristics in the first quadrant of the
magnetization curve as much as possible, it is desirable to
set the magnitude of the magnetic field value H2 as large
as possible within the extent that the magnetic properties
10 of the measurement sample S are not restored. Therefore,
it is necessary to improve the accuracy of selection of the
magnetic field value H2 by the external load environment
determination unit 18. For this purpose, an effective
method is to predict the magnetic field value H2 with
15 reference to B-H characteristic data acquired by
measurement of a sample that is equivalent to the
measurement sample S. It is possible to improve prediction
accuracy of this method by using machine learning.
[0066] As described above, in the second embodiment,
20 magnetic-field sweep control is performed in the loaded
state after selecting, as the magnetic field value H2 which
is the sweep start value Hs, a value that is smaller by X
percent than the magnetization force Hmax that is the
maximum value in the unloaded state. Therefore, a strong
25 magnetic field is not applied externally to the measurement
sample S at the time of magnetic field sweep. As a result,
it is possible to accurately measure the deterioration
state of magnetic properties of the measurement sample S to
which an external load is applied. In addition, since
30 magnetic properties in the first quadrant can also be
acquired in the loaded state, demagnetizing field
correction can be performed with high accuracy. It is thus
possible to accurately estimate the deterioration state of
29
the magnetic properties of magnetic material included in a
motor device. Note that, in the second embodiment, for
acquiring magnetic properties in the loaded state returning
from the third quadrant to the first quadrant via the
5 fourth quadrant, the value H=H2 just needs to be set as the
sweep end value He.
[0067] Third Embodiment.
A vibrating sample magnetometer according to a third
embodiment will be described with reference to FIGS. 10 and
10 11. FIG. 10 is a process chart showing an example of a
measurement procedure of the vibrating sample magnetometer
according to the third embodiment. FIG. 11 is a diagram
illustrating magnetic properties (B-H loop) obtained under
the second measurement condition (P1,T0) in a loaded state
15 in the third embodiment. In the third embodiment, the
magnetic properties of the measurement sample S being
subjected to a load are acquired by use of a method of
first order reversal curve (FORC) analysis. In FORC
measurement, when a magnetization curve is measured by the
20 sweeping of a magnetic field in a negative direction from a
positive saturation state, a magnetic field sweep direction
is reversed at a magnetic field value Hr during
demagnetization, and the magnetic field H is swept again
toward positive saturation. As this process is
25 sequentially performed while the magnetic field value Hr is
gradually changed, the inside of a hysteresis curve is
filled with FORCs. The FORC analysis visualizes
information about a magnetization process inside the bulk
of a measurement sample.
30 [0068] First, as described with reference to FIG. 5, the
control device 10 sets the measurement condition of the
measurement sample S in the initial state to the first
measurement condition (P0,T0) described above that is in
30
the unloaded state. The pressure P0=0 MPa, and the
temperature T0=25°C. In addition, the control device 10
performs full-loop magnetic-field sweep control of
controlling the excitation electromagnet 5a to apply the
5 external magnetic field H to the measurement sample S.
That is, the external magnetic field is swept from zero
(H=0) to the positive-side limit value “Hlmt”, swept from
the positive-side limit value “Hlmt” to the negative-side
limit value “-Hlmt”, and swept from the negative-side limit
10 value “-Hlmt” to the positive-side limit value “Hlmt”.
According to the magnetic-field sweep control under the
first measurement condition (P0,T0), a full-loop B-H loop
can be acquired as illustrated in FIG. 5 (step S300).
[0069] Next, the control device 10 applies the external
15 magnetic field H to the measurement sample S such that the
external magnetic field H changes from zero (H=0) to the
positive-side limit value “Hlmt” of the measuring
instrument, while keeping the measurement condition of the
measurement sample S to the first measurement condition
20 (P0,T0) that is in the unloaded state.
[0070] Next, the control device 10 reduces the external
magnetic field H to the magnetic field value H2, as in the
second embodiment, where H2