JP3454472B2 - Manganese-zinc ferrite and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manganese-zinc system ferrite and a method for producing the same, and more particularly to a manganese-zinc system ferrite having a high initial magnetic permeability .mu.i and a method for producing the same which are preferably used in a core of a transformer for wide band transmission.

[0002]

2. Description of the Related Art In the above wide band transmission transformer, for example, a pulse transformer, in order to perform accurate digital communication, the magnetic permeability is high in the wide band and is 10 to 500 kHz.
There is a need for a manganese-zinc-based ferrite for a core that exhibits a high magnetic permeability over the entire area.

Due to such a requirement, the applicant of the present invention has proposed, in Japanese Unexamined Patent Publication No. 6-204025, a manganese-zinc type ferrite having a high magnetic permeability in a wide band and a high magnetic permeability in the entire range of 10 to 500 kHz. The manganese-zinc system ferrite proposed in this patent publication is Fe ₂ O.
50 to 56 mol% of iron oxide in terms of ₃ and 2 in terms of MnO
2 to 39 mol% manganese oxide and 8 to 2 in terms of ZnO
A manganese-zinc-based ferrite containing 5 mol% of zinc oxide, which is sintered by adding a bismuth oxide component of 800 ppm or less in terms of Bi ₂ O ₃ and a molybdenum oxide component of 1200 ppm or less in terms of MoO _3. It was done.

The manganese-proposed in this patent publication
Zinc-based ferrite has 10 kHz at 25 ° C, 10
Initial permeability of 0 kHz and 500 kHz is 9 respectively
High initial magnetic permeability in a wide band of 000 or more, 9000 or more, and 3000 or more.

[0005]

In order to realize miniaturization and high-speed communication in the pulse transformer as described above, it is important to exhibit a higher initial permeability particularly in a low frequency region of about 10 kHz. . As a result, even if the number of windings is reduced, the rise of the output pulse can be made steep and the operation attenuation amount can be reduced, so that accurate digital communication can be performed.

Therefore, an object of the present invention is to provide a manganese-zinc system ferrite which exhibits a high initial permeability in a wide band, and particularly a high initial permeability in a low frequency region of about 10 kHz, and a manufacturing method thereof. .

[0007]

[Means for Solving the Problems] (1) 50 to 56 mol% of iron oxide in terms of Fe ₂ O ₃ and 22 to _{3 in} terms of MnO
It contains 9 mol% of manganese oxide and 8 to 25 mol% of zinc oxide in terms of ZnO as main components, and a bismuth oxide component of 800 ppm or less in terms of Bi ₂ O ₃ as a subcomponent with respect to the main component. , And a molybdenum oxide component of 1200 ppm or less in terms of MoO ₃ and having an average crystal grain size of 50 μm.
A manganese-zinc-based ferrite having an initial magnetic permeability μi of more than m and 150 μm or less and 10 kHz at 10 kHz or more. (2) The manganese-zinc system ferrite of (1) above, further containing 50 to 500 ppm of calcium oxide in terms of CaO. (3) Magnetic flux density B = 100 at a frequency of 10 kHz
The magnetic permeability μ ₁₀₀ when measured in millitesla is 1.2 of the magnetic permeability μ ₁ when measured in magnetic flux density B = 1 millitesla.
Manganese-zinc system ferrite of said (1) or (2) which is 0 times or more. (4) The manganese-zinc-based ferrite according to any one of the above (1) to (3), which has at least one temperature lowering step during firing. (5) 50 to 56 mol% of iron oxide in terms of Fe ₂ O ₃ and 22 to 39 mol% of manganese oxide in terms of MnO;
It contains 8 to 25 mol% of zinc oxide in terms of ZnO as a main component, and Bi ₂ O as a sub-component with respect to the main component.
800ppm or less bismuth oxide component in terms of ₃ and MoO
_It has a molybdenum oxide component of 1200 ppm or less in terms of ₃ and an average crystal grain size of more than 50 μm and 150 μm or less,
A method for producing a manganese-zinc-based ferrite having an initial permeability μi at 10 kHz of 20,000 or more,
During firing, a main temperature holding step of 1200 to 1450 ° C. is provided, and a temperature lowering step during firing is provided before the main temperature holding step,
The minimum temperature of the temperature lowering step during firing is 1150 to 1400.
A method for producing a manganese-zinc-based ferrite, characterized in that the temperature is set to a temperature range of 0 ° C and is set to be lower than the holding temperature of the main temperature holding step by at least 50 ° C or more.

[0008]

In the present invention, the holding temperature of the main temperature holding step during firing of the manganese-zinc ferrite is set to a temperature range of 1200 to 1450 ° C., and the firing is performed before the main temperature holding step. A temperature lowering step is provided, and the minimum temperature of the temperature lowering step during firing is within a temperature range of 1150 to 1400 ° C. and is lower than the holding temperature of the main temperature holding step by at least 50 ° C. or less (this temperature is hereinafter referred to as “lowering temperature” ) By setting, abnormal crystal growth does not occur, the average crystal grain size is more than 50 μm and 150 μm or less, and the initial magnetic permeability at 10 kHz is preferably 20,0.
A manganese-zinc system ferrite having a size of 00 or more was obtained. As a result, when the core obtained from the manganese-zinc ferrite of the present invention is incorporated in, for example, a pulse transformer, even if the number of windings is reduced, the rise of the output pulse can be made steep, and the amount of operation attenuation can be reduced. Therefore, the size can be reduced, and more accurate digital communication and the like can be performed at high speed.

Further, the manganese-zinc system ferrite of the present invention is 1
Since the initial permeability at 00 kHz is also equal to or higher than that, when the transformer is used, the number of windings can be reduced and the transformer can be downsized.

Furthermore, the manganese-zinc system ferrite of the present invention has a magnetic flux density B = 100 at 10 kHz.
The magnetic permeability μ ₁₀₀ when measured in millitesla is 1.2 of the magnetic permeability μ ₁ when measured in magnetic flux density B = 1 millitesla.
It shows a unique property of being 0 times or more. By the way, the maximum magnetic permeability μ ₁₀₀ / permeability μ ₁ of the conventional manganese-zinc-based ferrite is about 1.10 times.

Incidentally, Japanese Patent No. 2914554 discloses that
As a method capable of producing a high-permeability, high-permeability manganese-zinc-based ferrite with extremely high efficiency and low cost, a production method of firing manganese-zinc-based ferrite twice or more is disclosed. According to the disclosed manufacturing method, a temperature lowering process during firing having the same concept as the temperature lowering process during firing of the present invention is shown, but the minimum temperature of the temperature lowering process during firing is 1
It is preferably 100 ° C. or lower, preferably 1000 ° C. or lower, and more preferably 500 ° C. or lower. From this description, it can be understood that the lower the minimum temperature of the temperature lowering step during firing is, the more preferable.

On the other hand, in the present invention, the minimum temperature of the temperature lowering step during firing is set in the temperature range of 1150 to 1400 ° C. Further, in the present invention, the lowering temperature in the temperature lowering step during firing may be 30 ° C. or higher, particularly 50 ° C. or higher. In the present invention, the reason why the minimum temperature in the temperature lowering step during firing is set in the temperature range of 1150 to 1400 ° C will be described later, but in the firing method of the present invention,
The time required for the temperature lowering step during firing of the above conventional firing method can be shortened, and as a result, the overall manufacturing time can be shortened.

Further, the present invention mainly aims to improve the initial magnetic permeability in a low frequency region of about 10 kHz, whereas the conventional example described above aims to improve the initial magnetic permeability in a high frequency region of 100 kHz or more, Both are different in terms of purpose.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The specific constitution of the present invention will be described in detail below. In the method for producing a manganese-zinc-based ferrite of the present invention, the holding temperature of the main temperature holding step during firing of the molded body of the ferrite material after calcination is 1200 to 1
The temperature range is set to 450 ° C., particularly 1350 to 1450 ° C., and a temperature lowering process during firing is provided before the main temperature holding process,
The minimum temperature of the temperature lowering step during firing is 1150 to 1400.
It is characterized in that the temperature is in the temperature range of 0 ° C. and the above-mentioned lowering temperature is set to 30 ° C. or higher, particularly 50 ° C. or higher.

The holding temperature in the main temperature holding step is set to 1200.
The reason why the temperature range is set to ˜1450 ° C. is to promote ferritization and control of the crystal grain size, and the initial magnetic permeability at 10 kHz is particularly improved in this temperature range. The temperature holding time of this main temperature holding step is preferably about 0.5 to 10 hours.

The minimum temperature of the temperature lowering step during firing is
The reason for setting the temperature range of 1150 to 1400 ° C. is considered to be to alleviate the stress generated between the crystal grains and the grain boundaries.

This minimum temperature is preferably 1150-150.
It is 1350 ° C, particularly 1150 to 1300 ° C, and more preferably 1200 to 1300 ° C.

Further, if the above-mentioned lowering temperature is less than 50 ° C., the effect of lowering the temperature during firing is weak, and the initial permeability at 10 kHz is not sufficiently improved. This lowering temperature is preferably 100 to 250 ° C., particularly preferably 150 to 20 ° C.
It is 0 ° C.

In the temperature lowering step during firing, a temperature holding step at the above-mentioned minimum temperature may be provided. When the temperature holding step at this minimum temperature is provided, it is preferably within 3.0 hours.

The temperature lowering rate in the temperature lowering step during firing is 20
~ 300 ° C / hour, preferably 30-200 ° C / hour,
The temperature rising rate is 20 to 300 ° C./hour, preferably 30 to 2
It is preferably set to 00 ° C./hour. The temperature lowering step during firing is preferably performed within 6.0 hours.

The temperature lowering step during firing is not essential for obtaining the manganese-zinc type ferrite of the present invention, but it is preferably provided immediately before the main temperature holding step.

Before the temperature lowering step during firing, a sub-firing step or a sub-temperature holding step is provided. In this sub-firing process or sub-temperature holding process, the maximum temperature is
The same as or lower than the holding temperature of the above main temperature holding step,
In addition, it is necessary to be higher than the minimum temperature of the temperature lowering step during firing, and specifically, about 1150 to 1400 ° C is preferable. This maximum temperature is 5.
You may hold | maintain in the range within 0 hour. In the following description, a momentary holding time that appears as a peak at the highest temperature is also referred to as a sub-temperature holding step.

In the firing of the present invention, the same temperature profile as in the conventional firing can be used for the temperature raising step up to the sub-temperature holding step and the temperature lowering step following the main temperature holding step. Specifically, the rate of temperature rise in the temperature raising step is preferably 20 to 500 ° C./hour. Further, this heating rate can be changed in two or more steps. In this case, it is preferable to increase the initial heating rate and gradually decrease the heating rate. For example, in the case of two steps, it is preferable that the first step heating rate is about 200 to 500 ° C./hour and the second step heating rate is about 20 to 200 ° C./hour. On the other hand, the temperature lowering rate in the temperature lowering step is preferably 20 to 500 ° C./hour.
The temperature lowering rate in this temperature lowering step can also be changed in two or more stages, and in the case of two stages, the first stage temperature lowering rate is about 20 to 200 ° C./hour, and the second stage temperature lowering rate is 2.
It is preferable to set it to about 00 to 500 ° C./hour.

In the firing of the present invention, the furnace used may be a continuous furnace or a batch furnace. The atmosphere during firing is
It may be adjusted according to the theory of equilibrium oxygen partial pressure, and in particular, a nitrogen atmosphere in which the oxygen partial pressure is controlled (oxygen only exists)
Is preferable.

Even by the firing of the present invention under the above conditions, the average crystal grain size is more than 50 and 150 μm or less, and 1
A manganese-zinc based ferrite having an initial magnetic permeability at 0 kHz of 20,000 or more is obtained.

The average crystal grain size of the manganese-zinc ferrite of the present invention is preferably more than 50 to 150 μm, more preferably 60 to 130 μm, and particularly preferably 70 to 1
It is 20 μm. Further, in the manganese-zinc system ferrite of the present invention, one having a crystal grain size of more than 50 to 140 μm is preferably 50 vol% or more, and particularly 70 vol%.
Above, more preferably 80 vol% or more. In addition, the manganese-zinc-based ferrite of the present invention 10
The initial permeability at kHz is 20,000 or more, especially 2
It is preferably 5,000 or more. The initial permeability of the manganese-zinc system ferrite of the present invention at 10 kHz is currently about 35,000 at maximum, and the higher the value, the more preferable.

The manganese-zinc ferrite of the present invention is
At 10 kHz, the magnetic permeability μ ₁₀₀ when measured with the magnetic flux density B = 100 millitesla can be 1.20 times or more the magnetic permeability μ ₁ measured when the magnetic flux density B = 1 millitesla. This μ ₁₀₀ / μ ₁ is currently
We have achieved about 1.50 times.

The present invention can be applied to manganese-zinc type ferrites having a wide range of compositions, but the above main components are respectively 50 to 56 mol% in terms of Fe ₂ O _{3 and 2 in} terms of MnO.
It is preferable that the amount is 2 to 39 mol%, and the amount of ZnO is about 8 to 25 mol%. Outside this range, the initial magnetic permeability at 10 kHz tends to decrease.

Further, the manganese-zinc type ferrite of the present invention may contain calcium oxide or silicon dioxide as an accessory component. These subcomponents are
CaO conversion 50-500ppm, especially 100-300ppm
, Converted to SiO _{2 of} about 50 to 150 ppm. In addition,
CaO and SiO ₂ are generally present at grain boundaries.

Such a ferrite of the present invention comprises bismuth oxide and molybdenum oxide, particularly Bi ₂ O ₃ and MoO.
It is preferable to contain it in the form of ₃ . In this case, the added bismuth or molybdenum oxide component, especially the molybdenum oxide component, may be partially evaporated or sublimated by firing, and the content of the bismuth oxide or molybdenum oxide in the ferrite is equal to the addition amount. May not match. That is, the content of bismuth oxide, Bi ₂ O ₃ addition amount of about 50 to 100% by weight in terms of, also, the content of molybdenum oxide, the amount of about 10 to 60 wt% calculated as MoO _3, in particular 10 It is preferably about 30% by weight.

The ferrite of the present invention may further contain one or more of niobium oxide, indium oxide, vanadium oxide, tantalum oxide, zirconium oxide and the like, if necessary. These are Nb ₂ O ₅
Conversion, In ₂ O ₃ conversion, V ₂ O ₅ conversion, Ta ₂ O ₅ conversion,
It is preferable that the total amount is about 0 to 3000 ppm in terms of ZrO ₂ .

The average crystal grain size of the ferrite of the present invention containing such a component is preferably more than 50 μm and within 150 μm. 10k if average grain size is too large or too small
The initial magnetic permeability at Hz may decrease, and the initial magnetic permeability at 10 kHz may not be achieved. The average crystal grain size may be obtained as the average of the average diameters of the polycrystals observed by an optical microscope, which have been converted into circles, after acid-etching the mirror-polished surface.

When the average crystal grain size is large and uniform, the initial permeability at 25 ° C. at 10 kHz is 20,000 or more, particularly 25,000 or more, for example, 20,000 to 35,000. Yes, and 100
The initial magnetic permeability at kHz is 8,000 or more, particularly 9000 or more, and further 9500 or more, for example, about 9500 to 15,000. The initial magnetic permeability at 500 kHz is 2,000 or more, especially 300.
0 or more, further 3500 or more, for example 3500 to 60
The initial magnetic permeability of about 00, which is the same as or higher than the conventional one, can be obtained.

In order to produce the manganese-zinc type ferrite of the present invention, first, as a main component, a usual iron oxide component,
A mixture of a manganese oxide component and a zinc oxide component is prepared. These main components are mixed as the final composition of the ferrite so as to have the above-mentioned amount ratio, and are used as raw materials.
In addition, as a raw material of the sub-component, a compound or calcium oxide that becomes calcium oxide by firing such as calcium carbonate,
A compound that becomes silicon oxide by firing, silicon oxide, or the like is added. In this case, the raw materials of these subcomponents are added so that the final composition of the magnetic material has the above-mentioned amount ratio.

Then, a bismuth oxide component and a molybdenum oxide component are further added. As the bismuth oxide component, Bi ₂ O ₃ and Bi ₂ (SO ₄ ) ₃ can be used, but Bi ₂ O ₃ is preferable. The addition amount of the bismuth oxide component is 800 ppm or less, particularly 600 ppm or less, and preferably 100 to 400 ppm in terms of Bi ₂ O ₃ . If the amount added exceeds the above range, the initial magnetic permeability will decrease.

As the molybdenum oxide component, Mo is used.
O₃ Other than MoCl₃ Etc. can be used, but Mo
O₃ Is preferred. The addition amount of molybdenum oxide component is M
oO ₃ Converted to 1200ppm, especially below 1000ppm
It is preferably 100 to 1000 ppm. The amount added is within the above range
On the contrary, when it exceeds the enclosure, the initial permeability decreases. It should be noted that
Depending on niobium oxide, indium oxide, vanadium oxide
At least one of aluminum, tantalum oxide, and zirconium oxide
Is added to the raw material mixture.

After mixing the main component and the minor component to be added in this way, a small amount of an appropriate binder, for example, polyvinyl alcohol, for example, 0.1 to 1.0% by weight is added thereto,
Using a spray dryer or the like, make granules with a diameter of about 80 to 200 μm and mold.

Next, this molded product is fired. The firing conditions are as described above.

As described above, the manganese-zinc type ferrite of the present invention can be obtained.

[0040]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention. Example 1 MnO (24 mol%), ZnO (23 mol%), Fe ₂
O ₃ (53 mol%) as a main component and CaC as a secondary component
O ₃ (200 in terms of CaO in the final composition of the magnetic material
ppm) and SiO ₂ (100 in the final composition of the magnetic material)
ppm) and Bi ₂ O ₃ (200ppm) and MoO ₃ (200ppm)
) And were added to obtain a sample.

After mixing these, a binder was added and the mixture was granulated with a spray dryer to an average particle size of 150 μm and molded to obtain 100 molded products. In an atmosphere in which the oxygen partial pressure was controlled, 50 pieces each were fired according to the temperature profile shown in FIG. 1 (Example) and FIG. 2 (Comparative example), and the outer diameter was 6 mm, the inner diameter was 3 mm, and the height was 1. A toroidal core of 5 mm was obtained.

The temperature profiles shown in FIG. 1 (Example) and FIG. 2 (Comparative Example) will be described in detail below.

Temperature profile heating step of Example Temperature rising rate up to 1200 ° C .: 300 ° C./hour Temperature rising rate from 1200 ° C. to 1300 ° C .: 100 ° C./hour
Time Sub-temperature holding process 1300 ° C Hold for 1.0 hour Temperature lowering process during firing Minimum temperature: 1200 ° C (difference from holding temperature of main temperature holding process: 200 ° C) Temperature falling rate from 1300 ° C to 1200 ° C: 100 ° C /
Time increase rate from 1200 ° C to 1400 ° C: 100 ° C /
Time Main temperature holding step 1400 ° C, 3.0 hours holding Temperature dropping step 1400 ° C to 1000 ° C Temperature falling rate: 100 ° C /
Cooling rate from 1000 ℃ to normal temperature: 250 ℃ / hour

Temperature profile heating step of comparative example Temperature rising rate up to 1200 ° C .: 300 ° C./hour Temperature rising rate from 1200 ° C. to 1400 ° C .: 100 ° C./hour
No auxiliary temperature holding step No temperature lowering step during firing No main temperature holding step 3.0 hours holding at 1400 ° C Temperature dropping step from 1400 ° C to 1000 ° C: 100 ° C /
Cooling rate from 1000 ℃ to normal temperature: 250 ℃ / hour

That is, the temperature profile of the comparative example was obtained by removing the sub-temperature holding step and the temperature lowering step during firing from the temperature profile of the example.

The final compositions of the examples and comparative examples were measured by fluorescent X-ray.
i substantially corresponds to the raw material composition, and bismuth oxide and molybdenum oxide were 10 to 80% by weight of the added amounts.

The average crystal grain size of each of the obtained toroidal cores at 25 ° C., the initial magnetic permeability at 10 kHz, 100 kHz and 500 kHz was measured. An impedance analyzer was used to measure the magnetic permeability. The results are shown in Table 1.

[0048]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, according to the present invention, the average crystal grain size is 5
2 to 146 μm, especially the initial magnetic permeability at 10 kHz is much larger than the conventional one, and 100 k
It can be seen that the initial magnetic permeability above Hz is equal to or higher than the conventional one. Also, in the example, 50
Crystals having a particle size of from super to 140 μm were 80 vol% or more.

Furthermore, one sample of the embodiment and the comparative example is prepared.
Each at 10 kHz,
Magnetic permeability under magnetic flux density of 1 and 100 millitesla
(Μ₁, Μ ₁₀₀) Was measured, in the example,
μ₁Is 32,500 and μ₁₀₀Is 49,700,
 μ₁₀₀/ Μ₁Was 1.53, but in the comparative example, μ₁
Is 12,500 and μ₁₀₀Is 13,900,
₁₀₀/ Μ₁Was 1.11. Also, these examples
And the cross section of the sample of the comparative example was polished and photographed with an optical microscope.
The shaded photographs are shown in FIGS. 3 and 4, respectively.

Example 2 The composition of the manganese-zinc ferrite was the same as that of Example 1 except that the main components were the same as those of Example 1 and the auxiliary components of Samples 12 and 13 were CaCO ₃ and SiO _2. In 14 to 16, without adding these, Bi
Core samples 12 to 16 of Examples and Comparative Examples were obtained in the same manner as in Example 1 except that the amounts of ₂ O ₃ and MoO ₃ added were as described below.

Sample 12 Bi ₂ O ₃ : 300ppm MoO ₃ : 0 Sample 13 Bi ₂ O ₃ : 300ppm MoO ₃ : 300ppm Sample 14 Bi ₂ O ₃ : 400ppm MoO ₃ : 400ppm Sample 15 Bi ₂ O ₃ : 600ppm MoO ₃ : 200ppm sample _{16 Bi 2 O 3: 200ppm MoO} 3: 800ppm

When the initial magnetic permeability and the like of the cores of the above 12 to 16 samples were measured in the same manner as in Example 1, the same tendency as in Example 1 was obtained.

[0054]

The manganese-zinc type phyllite of the present invention exhibits a particularly high initial permeability in a low frequency region of about 10 kHz. Moreover, it has an initial permeability equal to or higher than that of the conventional one even in a high frequency region of 100 kHz or more.

[Brief description of drawings]

FIG. 1 is a diagram showing a temperature profile in firing in an example.

FIG. 2 is a diagram showing a temperature profile in firing of a comparative example.

FIG. 3 is a drawing-substituting photograph of a cross section of a sample of the present invention.

FIG. 4 is a drawing-substitute photograph of a cross section of a comparative sample.

Claims (5)

(57) [Claims] 1. Main components are 50 to 56 mol% iron oxide in terms of Fe ₂ O ₃ , 22 to 39 mol% manganese oxide in terms of MnO, and 8 to 25 mol% zinc oxide in terms of ZnO. Contains 8 as Bi ₂ O ₃ as an auxiliary component to the above main component.
Bismuth oxide component of less than 00ppm and 1 in terms of MoO ₃
A manganese-zinc-based ferrite having a molybdenum oxide content of 200 ppm or less, an average crystal grain size of more than 50 μm and 150 μm or less, and an initial magnetic permeability μi at 10 kHz of 20,000 or more. 2. The manganese-zinc system ferrite according to claim 1, which further contains 50 to 500 ppm of calcium oxide in terms of CaO. 3. A magnetic flux density B = 1 at a frequency of 10 kHz.
The manganese-zinc system ferrite according to claim 1 or 2, wherein the magnetic permeability µ ₁₀₀ when measured at 00 millitesla is 1.20 times or more the magnetic permeability µ ₁ when measured at magnetic flux density B = 1 millitesla. 4. The manganese-zinc system ferrite according to claim 1, which has at least one temperature lowering step during firing. 5. Main components are 50 to 56 mol% of iron oxide in terms of Fe ₂ O ₃ , 22 to 39 mol% of manganese oxide in terms of MnO, and 8 to 25 mol% zinc oxide in terms of ZnO. Contains 8 as Bi ₂ O ₃ as an auxiliary component to the above main component.
Bismuth oxide component of less than 00ppm and 1 in terms of MoO ₃
A method for producing a manganese-zinc-based ferrite having a molybdenum oxide content of 200 ppm or less, an average crystal grain size of more than 50 μm and 150 μm or less, and an initial magnetic permeability μi at 10 kHz of 20,000 or more, which is during firing. , A main temperature holding step of 1200 to 1450 ° C., and a temperature lowering step during firing is provided before the main temperature holding step,
The minimum temperature of the temperature lowering step during firing is 1150 to 1400.
A method for producing a manganese-zinc-based ferrite, characterized in that the temperature is set to a temperature range of 0 ° C and is set to be lower than the holding temperature of the main temperature holding step by at least 50 ° C or more.