TECHNICAL FIELD
[0001] The present invention relates to a production method of an Fe-based nanocrystalline
alloy core.
BACKGROUND ART
[0002] Fe-based nanocrystalline alloys have excellent soft magnetic characteristics that
reconcile both high saturation flux density Bs and high relative permeability µr,
and therefore are used as the cores in common mode choke coils, high-frequency transformers,
and the like.
[0003] Representative compositions of Fe-based nanocrystalline alloys are the Fe-Cu-M'-Si-B
type compositions (where M' is at least one element selected from the group consisting
of Nb, W, Ta, Zr, Hf, Ti and Mo), as described in Patent Document 1.
[0004] An Fe-based nanocrystalline alloy is obtained by, for an alloy in liquid phase which
has been heated to the melting point or a higher temperature, rapidly solidifying
the alloy to obtain an amorphous alloy, and then applying a heat treatment to the
amorphous alloy in order to effect fine-crystallization (nanocrystallization) thereof.
As a method of rapidly solidifying a liquid phase, for example, a single-roll method
may be adopted, which provides good producibility. An alloy that is obtained through
rapid solidification is in a thin strip or ribbon shape.
[0005] Depending on the temperature profile during heat treatment, or with application of
a magnetic field in a specific direction during heat treatment, an Fe-based nanocrystalline
alloy may acquire different magnetic characteristics, with respect to the relative
permeability µ, squareness ratio, and so on.
[0006] For example, Patent Document 2 proposes performing a heat treatment while applying
a magnetic field in the width direction (i.e., the height direction of the core) of
an alloy ribbon, in order to obtain an Fe-based nanocrystalline alloy having an initial
relative permeability µi of 70,000 or more and a squareness ratio of 30% or less.
While various profiles are proposed in Patent Document 2 as specific examples of the
heat treatment, they can be generally classified into: profiles which keep a state
under magnetic field application in a maximum reachable temperature region of the
heat treatment; profiles which keep a state under magnetic field application during
temperature elevation, through a maximum reachable temperature region, and over into
a cooling process; and profiles which keep a state under magnetic field application
from a maximum reachable temperature region and into a cooling process.
[0007] Patent Document 3 relates to a nanocrystalline alloy exhibiting high magnetic permeability
at a low square ratio.
[0008] Patent Document 4 describes obtaining a magnetic core having a small diameter which
exhibits a high permeability.
[0009] Patent Document 5 discloses a nanocrystalline soft magnetic alloy ribbon.
[0010] Patent Document 6 discloses a magnetic core obtained by winding a long sheet of thin
alloy or by laminating short sheets thereof.
CITATION LIST
PATENT LITERATURE
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0012] The heat treatment method which is disclosed in Patent Document 2 above is considered
effective as a means for lowering the squareness ratio.
[0013] As one application, an ability to cope with lower frequencies to higher frequencies,
specifically from the 10 kHz band to the 1 MHz band, this being a frequency band for
use in a common mode choke, is being desired.
[0014] A characteristic index which is often used of a common mode choke is the impedance
relative permeability µrz. The impedance relative permeability µrz is described in,
for example, C2531 of the JIS standards (revised 1999). As indicated by the expression
below, an impedance relative permeability µrz can be considered equal to an absolute
value of complex relative permeability (µr'-iµr'') (see, for example, "
Know-hows on Magnetic Material Selection", November 10, 1989, editor: Keizo OHTA):
[0015] In the above expression, the real part µr' of complex relative permeability represents
a magnetic flux density component without a phase lag relative to the magnetic field,
and generally corresponds to the magnitude of impedance relative permeability µrz
in a low frequency region. On the other hand, the imaginary part µr'' represents a
magnetic flux density component including a phase lag relative to the magnetic field,
and is equivalent to a loss in magnetic energy. In a high frequency region (e.g.,
50 kHz or above), the effect of noise suppression is greater as the imaginary part
µr'' becomes higher.
[0016] The impedance relative permeability µrz that is represented by the above expression
is used as an index for assessing the effect of noise suppression for a wide frequency
band. The impedance relative permeability µrz having a high value across a wide frequency
band means a good ability to absorb or remove common mode noise.
[0017] The inventor has conducted a study in order to enhance the aforementioned impedance
relative permeability µrz in a wide band across frequencies from 10 kHz to 1 MHz.
As a result, they have realized that it is difficult to obtain a high impedance relative
permeability µrz across a wide frequency band with the heat treatment profiles described
in Patent Document 1 and Patent Document 2.
[0018] The present invention, which has been made in view of the above, aims to provide
a method of producing the Fe-based nanocrystalline alloy core.
SOLUTION TO PROBLEM
[0019] The inventor has found that, in effecting fine-crystallization (nanocrystallization)
of an Fe-based amorphous alloy through a heat treatment, applying a magnetic field
within only a specific temperature range in a period of temperature elevation produces
an Fe-based nanocrystalline alloy core which has a high impedance relative permeability
µrz in a wide band across frequencies from 10 kHz to 1 MHz, thus arriving at the present
invention.
<1> Fe-based nanocrystalline alloy core
[0020] A core is produced, after winding an Fe-based amorphous alloy ribbon that is capable
of nanocrystallization, through a heat treatment step of heating the Fe-based amorphous
alloy ribbon up to a crystallization temperature region and cooling the Fe-based amorphous
alloy ribbon, wherein
the core has an impedance relative permeability µrz of 90,000 or more at a frequency
of 10 kHz,
40,000 or more at a frequency of 100 kHz, and
8,500 or more at a frequency of 1 MHz.
[0021] In one embodiment, it is preferable that the core has an impedance relative permeability
µrz of
105,000 or more at a frequency of 10 kHz,
45,000 or more at a frequency of 100 kHz, and
9,000 or more at a frequency of 1 MHz.
[0022] In one embodiment, it is preferable that the Fe-based nanocrystalline alloy ribbon
has a thickness of not less than 9 µm and not more than 20 µm.
<2> Production method for Fe-based nanocrystalline alloy core
[0023] A production method for a core according to an embodiment of the present invention
comprises, after winding an Fe-based amorphous alloy ribbon that is capable of nanocrystallization,
a heat treatment step of heating the Fe-based amorphous alloy ribbon up to a crystallization
temperature region and cooling the Fe-based amorphous alloy ribbon, wherein the heat
treatment step comprises a magnetic field application step of applying a magnetic
field in a height direction of the core for not less than 10 minutes and not more
than 60 minutes, within only a temperature range in a period of temperature elevation
spanning from a temperature which is 25°C higher than a crystallization onset temperature
by differential scanning calorimeter to a temperature which is 60°C higher than the
crystallization onset temperature.
[0024] In a production method according to an embodiment of the present invention, it is
preferable that the heat treatment step comprises a magnetic field application step
of applying a magnetic field in the height direction of the core for not less than
15 minutes and not more than 40 minutes, within only a temperature range in the period
of temperature elevation from a temperature which is 30°C higher than a crystallization
onset temperature by differential scanning calorimeter to a temperature which is 50°C
higher than the crystallization onset temperature.
[0025] In a production method according to an embodiment of the present invention, it is
preferable that, in the magnetic field application step, a magnetic field with a magnetic
field intensity of not less than 50 kA/m and not more than 300 kA/m is applied in
the height direction of the core.
[0026] In a production method according to an embodiment of the present invention, an Fe-based
nanocrystalline alloy ribbon having a thickness of not less than 9 µm and not more
than 20 µm is preferably used.
[0027] In an embodiment of the present invention, a production method for an Fe-based nanocrystalline
alloy ribbon comprises: a step of providing an Fe-based amorphous alloy ribbon that
is capable of nanocrystallization; a step of winding the Fe-based amorphous alloy
ribbon to form a wound body; a heat treatment step of heating the wound body up to
a crystallization temperature region and cooling the wound body; and a step of, during
the heat treatment step, applying a magnetic field to the wound body, wherein, in
a period of temperature elevation during the heat treatment step, within at least
a partial period in a temperature range from a temperature which is 25°C higher than
a crystallization onset temperature as indicated by a differential scanning calorimeter
to a temperature which is 60°C higher than the crystallization onset temperature,
the step of applying a magnetic field applies a magnetic field of a predetermined
intensity (e.g., 50 kA/m) or greater in a height direction of the wound body (i.e.,
a width direction of the alloy ribbon), but does not apply a magnetic field of the
predetermined intensity or greater to the wound body within a partial period in the
period of temperature elevation. More specifically, a magnetic field is applied within
only a temperature range from a temperature which is 25°C higher than the crystallization
onset temperature to a temperature which is 60°C higher than the crystallization onset
temperature, for a period of time which is not less than 10 minutes and not more than
60 minutes, whereas no magnetic field application is performed in temperature regions
other than the aforementioned temperature range in the period of temperature elevation.
In this step, a magnetic field of the predetermined intensity or greater is not applied
in a period of temperature elevation at the crystallization onset temperature or below,
or when at the highest temperature of the heat treatment step (i.e., a temperature
which is more than 60°C higher than the crystallization onset temperature).
ADVANTAGEOUS EFFECTS OF INVENTION
[0028] According to an embodiment of the present invention, an Fe-based nanocrystalline
alloy core which has a high impedance relative permeability µrz in a wide frequency
band across frequencies from 10 kHz to 1 MHz can be obtained. Moreover, it is possible
to fabricate such an Fe-based nanocrystalline alloy core. Therefore, it finds optimum
use in a common mode choke or the like where characteristics in a wide frequency band
across frequencies from 10 kHz to 1 MHz are important.
BRIEF DESCRIPTION OF DRAWINGS
[0029]
[FIG. 1] A diagram describing a profile of heat treatment and magnetic field application
according to Example 1 of the present invention.
[FIG. 2] A diagram describing a profile of heat treatment and magnetic field application
according to Example 2 of the present invention.
[FIG. 3] A diagram describing a profile of heat treatment and magnetic field application
(no magnetic field) according to Comparative Example 1.
[FIG. 4] A diagram describing a profile of heat treatment and magnetic field application
according to Comparative Example 2.
[FIG. 5] A diagram showing results of measurement for an Fe-based amorphous alloy
ribbon according to Example 1 by a differential scanning calorimeter (DSC).
[FIG. 6] A graph showing how impedance relative permeability µrz may change in frequency
characteristics, between different manners of magnetic field application during a
heat treatment.
DESCRIPTION OF EMBODIMENTS
[0030] Hereinafter, with reference to the drawings, embodiments of the present invention
will be specifically described.
[0031] In an embodiment of the present invention, when applying a magnetic field in the
width direction of the wound ribbon (i.e., the height direction of the core) to obtain
an Fe-based nanocrystalline alloy, a heat treatment step is conducted while applying
a magnetic field within only a specific temperature range in a period of temperature
elevation.
[0032] Specifically, in a heat treatment step according to an embodiment of the present
invention, within only a temperature range in a period of temperature elevation from
a temperature which is 25°C higher than a crystallization onset temperature by differential
scanning calorimeter to a temperature which is 60°C higher than the crystallization
onset temperature, a magnetic field application step of applying a magnetic field
in the height direction of the core for a period of time which is not less than 10
minutes and not more than 60 minutes is performed.
[0033] Thus, core fabrication according to an embodiment of the present invention involves
applying a magnetic field within only a specific period in a period of temperature
elevation, while not applying any magnetic field when at the highest temperature of
heat treatment or in a period through the highest temperature into the cooling process.
In an embodiment of the present invention, the highest temperature of heat treatment
is typically a temperature that is higher than a temperature which is 60°C higher
than the crystallization onset temperature.
[0034] In the present specification, a "period of temperature elevation" means a period
before reaching the maximum reachable temperature, and may encompass any state of
warming, cooling, or retaining a constant temperature that may exist before the maximum
reachable temperature is reached. For example, as performed within a temperature range
in a period of temperature elevation from a temperature which is 25°C higher than
the aforementioned crystallization onset temperature to a temperature which is 60°C
higher than the crystallization onset temperature, the heat treatment may take place
in a manner of retaining a certain temperature within the aforementioned temperature
range for a certain period of time. Moreover, the temperature may be increased monotonically
with a constant temperature elevation rate, or the temperature elevation rate may
be changed along the way.
[0035] Now, the reasoning as to how the inventor has arrived at the aforementioned idea
of applying a magnetic field within only a specific temperature range in a period
of temperature elevation during the heat treatment step will be described.
[0036] FIG. 6 is a graph showing frequency characteristics of impedance relative permeability
as ascertained through an experiment by the inventor, illustrating the frequency characteristics
of impedance relative permeability of a core (core
C1) which was not subjected to magnetic field application during heat treatment, and
the frequency characteristics of impedance relative permeability of a core (core
C2) which was subjected to magnetic field application throughout the entire heat treatment
period.
[0037] As can be seen from FIG.
6, in a low frequency region of e.g. 100 kHz or less, the impedance relative permeability
µrz of the core
C1 (i.e., no magnetic field application) is considerably greater than the impedance
permeability µrz of the core
C2 (i.e., always under magnetic field application). On the other hand, in a high frequency
region above 1 MHz, the impedance permeability µrz of the core
C2 is observed to be higher than the impedance permeability µrz of the core
C1. From this, it was confirmed that applying a magnetic field during heat treatment
in order to confer magnetic anisotropy to the core tends to lower the impedance relative
permeability µrz (especially the real part µr' of complex relative permeability according
to the experiment by the inventor) in the low frequency region, but tends to improve
the impedance relative permeability µrz in the high frequency region.
[0038] Thus, the inventor saw a tradeoff between an improvement in impedance relative permeability
µrz on the low frequency side and an improvement in impedance relative permeability
µrz on the high frequency side. However, while going through various experiments related
to heat treatment in a magnetic field, the inventor came to realize that, in a heat
treatment at a low temperature and over a short period of time, conditions may exist
which would induce little decrease in impedance relative permeability on the low frequency
side, upon which they conducted further studies.
[0039] Consequently, it was found that: in a heat treatment step, a magnetic field in the
height direction of the core may be applied within only a temperature range in a period
of temperature elevation spanning from a temperature which is 25°C higher than a crystallization
onset temperature by differential scanning calorimeter to a temperature which is 60°C
higher than the crystallization onset temperature, for a period of time which is not
less than 10 minutes and not more than 60 minutes, whereby impedance relative permeability
µrz in the high frequency region can be improved while reducing a decrease in impedance
relative permeability µrz in the low frequency region. In particular, it was found
that applying a magnetic field within the aforementioned temperature range and for
only the aforementioned period of time not only reduces a decrease in impedance permeability
µrz in the low frequency region, but also may possibly provide an improvement over
the case of applying no magnetic field. As a result of this, a core having a high
impedance relative permeability µrz in a wide frequency band across frequencies from
10 kHz to 1 MHz was obtained.
[0040] As described above, with the heat treatment method which applies a magnetic field
within only a specific temperature range in a period of temperature elevation for
only a certain period of time, it is possible to obtain a core with a µrz of 90,000
to 115,000 at a frequency of 10 kHz, a µrz of 40,000 to 49,000 at a frequency of 100
kHz, and a µrz of 8,500 to 15,000 at a frequency of 1 MHz.
[0041] It is estimated that the aforementioned magnetic field application within only a
certain temperature range in a period of temperature elevation has enabled maximization
of the impedance relative permeability µrz in a wide frequency band across frequencies
from 10 kHz to 1 MHz. However, the mechanism as how to magnetic field application
within only a certain temperature range in a period of temperature elevation contribute
to each of µ' and µ" is yet undiscovered.
[0042] Note also that the aforementioned crystallization onset temperature is defined with
a differential scanning calorimeter. It is difficult to accurately measure the true
crystallization onset temperature, and it would be effective to identify it with a
differential scanning calorimeter (DSC: Differential Scanning Calorimetry). A temperature
at which an exothermic reaction that is due to nanocrystallization being begun during
ascending temperature is detected is defined as the crystallization onset temperature
(see FIG. 5). In the present specification, a crystallization onset temperature means
what is determined by using a differential scanning calorimeter under a measurement
condition such that the temperature elevation rate is 10°C/minute.
[0043] Control of the heat treatment temperature is preferably performed so that the temperature
distribution within the actual heat treatment furnace is within ± 5°C, while taking
into account the capacity of the heat treatment furnace and a calorific value associated
with crystallization of the amorphous alloy ribbon to be heat-treated. As a result,
magnetic characteristics of the heat-treated alloy can be stabilized.
[0044] The intensity of the magnetic field to be applied is preferably not less than 50
kA/m and not more than 300 kA/m. If the applied magnetic field is too weak, it will
be difficult to confer an induced magnetic anisotropy under practical operation conditions;
if it is too high, too much induced magnetic anisotropy tends to be conferred. A more
preferable range is from 60 kA/m to 280 kA/m.
[0045] It has been confirmed by the inventor that, when the applied magnetic field is a
relatively weak magnetic field which is less than 50 kA/m, the impedance relative
permeability is hardly affected even if it is applied in any period during the heat
treatment step. Therefore, in an embodiment of the present invention, application
of a weak magnetic field of less than 50 kA/m may well be regarded as no magnetic
field being applied at all.
[0046] As an Fe-based amorphous alloy that is capable of nanocrystallization, for example,
an alloy of a composition expressed by the general formula: (Fe
1-aM
a)
100-x-y-z-α-β-γCu
xSi
yB
zM'αM"βXγ (at%) (where M is Co and/or Ni; M' is at least one element selected from
the group consisting of Nb, Mo, Ta, Ti, Zr, Hf, V, Cr, Mn and W; M" is at least one
element selected from the group consisting of Al, platinum group elements, Sc, rare-earth
elements, Zn, Sn and Re; X is at least one element selected from the group consisting
of C, Ge, P, Ga, Sb, In, Be and As; a, x, y, z, α, β and γ respectively satisfy 0≤a≤0.5,
0.1≤x≤3, 0≤y≤30, 0≤z≤25, 5≤y+z≤30, 0≤α≤20, 0≤β≤20 and 0≤γ≤20) can be used.
[0047] By allowing an alloy of the above composition to be melted to its melting point or
above, and rapidly solidified by the single-roll method, a long length of amorphous
alloy ribbon (thin strip) can be obtained.
[0048] The thickness of the amorphous alloy ribbon is preferably not less than 9 µm and
not more than 30 µm. If it is less than 9 µm, the ribbon has insufficient mechanical
strength so that it is likely to break during handling. If it is above 30 µm, an amorphous
state cannot be stably obtained. When the amorphous alloy ribbon after nanocrystallization
is used as a core for a high frequency application, an eddy current will occur in
the ribbon; the loss due to the eddy current will be greater as the ribbon becomes
thicker. Therefore, a more preferable thickness is 9 µm to 20 µm, and a thickness
of 15 µm or less is still more preferable.
[0049] For a practical core shape, the width of the amorphous alloy ribbon is preferably
10 mm or more. While a wide width is preferable because slitting (i.e., cutting up)
a wide-width alloy ribbon permits low cost, a width of 250 mm or less is preferable
for stable fabrication of an alloy ribbon. In order to attain more stable fabrication,
a width of 70 mm or less is more preferable.
[0050] The heat treatment for nanocrystallization is preferably performed in an inert gas
such as nitrogen, and the maximum reachable temperature is preferably greater than
560°C but not more than 600°C. That of 560°C or less, or above 600°C is unpreferable
because of resulting in large magnetostriction. No particular time of retention at
the maximum reachable temperature may be set, i.e., 0 minutes (that is, no time of
retention), and nanocrystallization is still possible. Retention for 3 hours or less
may be observed in order to account for the heat capacity of the total amount of alloy
to be heat-treated and the stability of characteristics.
[0051] As a temperature profile of heat treatment, relatively rapid warming with a temperature
elevation rate of e.g. 3 to 5°C/minute may be effected from room temperature to near
a temperature at which nanocrystallize begins (typically, to a temperature which is
20°C lower than the crystallization onset temperature); and thereafter, warming may
be effected with a gentle temperature elevation rate with an average of 0.2 to 1.0°C/minute
from near the aforementioned nanocrystallization onset temperature to a temperature
which is 60°C higher than the nanocrystallization onset temperature (or alternatively
to the maximum reachable temperature), whereby stable nanocrystallization can take
place. Note that, from the maximum reachable temperature to 200°C, it is preferable
to perform cooling at a cooling rate of 2 to 5°C/minute. Usually at 100°C or less,
the alloy can be taken out into the atmospheric air.
[0052] For use as a magnetic part, an Fe-based amorphous alloy ribbon that is capable of
nanocrystallization may be wound into a toroidal body, and subjected to a heat treatment
step which involves heating up to the crystallization temperature region and then
cooling. By ensuring that application of a magnetic field at this time is in the height
direction of the aforementioned toroidal body (core), whereby a predetermined induced
magnetic anisotropy can be conferred.
[Examples]
(Example 1)
[0053] An alloy melt composed of Cu:1%, Nb:3%, Si:15.5% and B:6.5%, all by at%, with a balance
of Fe and inevitable impurities, was quenched by single-roll method, thereby obtaining
an Fe-based amorphous alloy ribbon having a width of 50 mm and a thickness of 13 µm.
After this Fe-based amorphous alloy ribbon was slit (cut up) in a width of 15 mm,
it was wound so as to have an outer diameter of 31 mm and an inner diameter of 21
mm, thereby producing a toroidal core (height: 15 mm). As shown in FIG. 5, a measurement
with a differential scanning calorimeter (DSC) indicated the crystallization onset
temperature of this alloy to be 500°C.
[0054] The produced core was subjected to a heat treatment and magnetic field application
according to the profile of temperature-and-magnetic field application as shown in
FIG. 1. The magnetic field application was performed in a temperature range from 530
to 550°C (a temperature range from a temperature which is 30°C higher than the crystallization
onset temperature to a temperature which is 50°C higher than the crystallization onset
temperature) for 30 minutes. The direction of magnetic field application was the width
direction of the alloy ribbon, i.e., the height direction of the core. The magnetic
field intensity was 280 kA/m. Note that the maximum reachable temperature during the
heat treatment was 580°C.
[0055] An impedance relative permeability µrz of the heat-treated core was measured at 10
kHz, 100 kHz and 1 MHz. The results are shown in Table 1.
[0056] Measurements of the impedance relative permeability µrz were taken by using HP4194A,
manufactured by Agilent Technologies, under conditions with an oscillation level of
0.5 V and an average of 16. Insulation coated leads were passed through the central
portion of the toroidal core, so as to be connected to input/output terminals, whereby
the measurements were taken.
[0057] In Example 1, the impedance relative permeability µrz was 98,000 at 10 kHz, 42,000
at 100 kHz, and 8,600 at 1 MHz.
[Table 1]
Frequency |
Example |
Example |
Example |
Example |
Comparative Example 1 |
Comparative Example 2 |
Reference Example |
10 kHz |
98,000 |
109,000 |
91,000 |
90,000 |
88,000 |
18,000 |
52,000 |
100 kHz |
42,000 |
47,000 |
46,000 |
46,000 |
41,000 |
17,500 |
37,000 |
1 MHz |
8,600 |
9,500 |
9,300 |
10,000 |
7,200 |
6,900 |
9,500 |
(Example 2)
[0058] By using the Fe-based amorphous alloy described in Example 1, a toroidal core was
similarly produced. The produced core was subjected to a heat treatment and magnetic
field application according to the profile of temperature-and-magnetic field application
as shown in FIG. 2. Only the temperature range and the magnetic field intensity of
magnetic field application were different from those in Example 1 (FIG.
1), while the other conditions were similar to those in Example 1.
[0059] The magnetic field application was performed for 15 minutes in a temperature range
from 540 to 550°C (a temperature range from a temperature which is 40°C higher than
the crystallization onset temperature to a temperature which is 50°C higher than the
crystallization onset temperature). The magnetic field intensity was 160 kA/m. Measurement
results of the impedance relative permeability µrz of the heat-treated core, at 10
kHz, 100 kHz and 1 MHz, are shown in Table 1.
[0060] In Example 2, the impedance relative permeability µrz was 109,000 at 10 kHz, 47,000
at 100 kHz, and 9,500 at 1 MHz. In other words, a higher impedance relative permeability
µrz than that of Example 1 was attained at each of the frequencies of 10 kHz, 100
kHz and 1 MHz.
(Example 3)
[0061] An alloy melt composed of Cu:1%, Nb:3%, Si:15.5% and B:6.5%, all by at%, with a balance
of Fe and inevitable impurities (similar to Example 1), was quenched by single-roll
method, thereby obtaining an Fe-based amorphous alloy ribbon having a width of 50
mm and a thickness of 10 µm. By using this Fe-based amorphous alloy ribbon having
a thickness of 10 µm (which was 13 µm in Example 1), a toroidal core was similarly
produced. Similarly to Example 2, the produced core was subjected to a heat treatment
and magnetic field application according to the profile of temperature-and-magnetic
field application as shown in FIG.
2. Measurement results of the impedance relative permeability µrz of the heat-treated
core at 10 kHz, 100 kHz and 1 MHz are shown in Table 1.
[0062] In Example 3, the impedance relative permeability µrz was 91,000 at 10 kHz, 46,000
at 100 kHz, and 9,300 at 1 MHz.
(Example 4)
[0063] By using the Fe-based amorphous alloy ribbon having a thickness of 13 µm described
in Example 1, a toroidal core was similarly produced. To the produced core, a magnetic
field was applied for 15 minutes in a heat treatment temperature range from 530°C
to 540°C and with an intensity of 160 kA/m. Measurement results of the impedance relative
permeability µrz of the heat-treated core at 10 kHz, 100 kHz and 1 MHz are shown in
Table 1.
[0064] In Example 4, the impedance permeability µrz was 90,000 at 10 kHz, 46,000 at 100
kHz, and 10,000 at 1 MHz.
(Comparative Example 1)
[0065] By using the Fe-based amorphous alloy described in Example 1, a toroidal core was
similarly produced. According to the profile of temperature-and-magnetic field application
as shown in FIG.
3, the produced core was subjected to a heat treatment without any magnetic field application
(i.e., under no magnetic field). As can be seen from FIG.
3, the temperature profile in Comparative Example 1 was similar to that in Example 1.
[0066] Measurement results of the impedance relative permeability µrz of the heat-treated
core at 10 kHz, 100 kHz and 1 MHz are shown in Table 1.
[0067] A comparison between Comparative Example 1 under no magnetic field application and
Examples 1 and 2 indicates that, at each frequency, the value of impedance relative
permeability µrz in Comparative Example 1 is smaller than the values in Examples 1
and 2.
(Comparative Example 2)
[0068] By using the Fe-based amorphous alloy described in Example 1, a toroidal core was
similarly produced. The produced core was subjected to a heat treatment and magnetic
field application, according to a profile of temperature-and-magnetic field application
which is shown in FIG.
4. As can be seen from FIG.
4, the temperature profile in Comparative Example 2 was similar to that in Example 1.
[0069] In Comparative Example 2, although the magnetic field intensity during magnetic field
application is similar to that in Example 1 (FIG.
1), the temperature range of magnetic field application spans from the beginning of
the heat treatment, through the maximum reachable temperature of 580°C, over into
the cooling. This temperature range of magnetic field application lies outside the
range according to the present invention.
[0070] Measurement results of the impedance relative permeability µrz of the heat-treated
core at 10 kHz, 100 kHz and 1 MHz are shown in Table 1.
[0071] A comparison between Comparative Example 2 and Examples 1 and 2 indicates that, at
each frequency, the value of impedance relative permeability µrz in Comparative Example
2 is smaller than the values in Examples 1 and 2.
(Reference Example)
[0072] As Reference Example, a magnetic field was applied to a toroidal core which was similar
in composition and shape to Example 2, in a lower temperature region and for a longer
time in a period of temperature elevation during the heat treatment step, and the
resultant impedance relative permeability thereof will now be described.
[0073] In this Reference Example, the magnetic field application was performed continuously
for about 60 minutes in a temperature range from 480 to 520°C (a temperature range
from a temperature which is 20°C lower than the crystallization onset temperature
to a temperature which is 20°C higher than the crystallization onset temperature).
The direction of magnetic field application was the width direction of the alloy ribbon,
i.e., the height direction of the core, and the magnetic field intensity was 120 kA/m.
[0074] Measurement results of the impedance relative permeability µrz of the heat-treated
core at 10 kHz, 100 kHz and 1 MHz are shown in Table 1.
[0075] FIG.
6 shows frequency characteristics of impedance relative permeability µrz of a core
(core
E1) according to an embodiment of the present invention (similar to Example 2) and a
core (core
R1) according to Reference Example above. FIG.
6 also shows a core (core
C1) under no magnetic field being applied, corresponding to Comparative Example 1, and
a core (core
C2) under continuous magnetic field application, corresponding to Comparative Example
2 above.
[0076] FIG.
6 would indicate that, as in the core
R1, if a magnetic field is applied for about 60 minutes in a temperature region near
the crystallization onset temperature that is lower than a temperature which is 25°C
higher than the crystallization onset temperature, the impedance relative permeability
µrz in the low frequency region may become lower than that under no magnetic field
application (core
C1). However, in a high frequency region above 100 kHz, the impedance relative permeability
tends to be higher for the core
R1 than for the core
C1.
[0077] On the other hand, as in an embodiment of the present invention (core
E1), if a magnetic field is applied only for a relatively short period of time above
or at 25°C from and below or at 60°C from the crystallization onset temperature (such
that typically no magnetic field is applied when at the highest temperature), improvements
in the impedance relative permeability µrz were confirmed not only in the high frequency
region but also in the low frequency region. Thus, among those modes of magnetic field
application which apply a magnetic field in a specific period before the maximum reachable
temperature, an embodiment of the present invention exhibits an outstanding effect
of improving the impedance relative permeability µrz in the low frequency region.
INDUSTRIAL APPLICABILITY
[0078] According to an embodiment of the present invention, there is provided a core which
exhibits a high impedance relative permeability µrz in a manner of supporting a wide
frequency band, which is suitably used for a common mode choke coil, a high-frequency
transformer, or the like.