JP2005306668A - Ferrite sintered body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite sintered body having a small absolute value of αμir(a relative temperature coefficient of initial magnetic permeability) in a wide temperature range of -40-140°C. <P>SOLUTION: This ferrite sintered body comprises, as main constituents, Fe<SB>2</SB>O<SB>3</SB>of 45.5-48 mol%, CuO of 5-10 mol%, ZnO of 26-30 mol% and the balance substantially NiO, and further comprises, as an additive, cobalt oxide of 0.005-0.045 wt.% in terms of CoO to the main constituents, and has an average crystal grain diameter of ≤5 μm. The absolute value of αμir can be made small by controlling the main constituents within the above range and by incorporating cobalt oxide by 0.005-0.045 wt.% in terms of CoO. Both the absolute value of αμir<SB>-40-20</SB>and the absolute value of αμir<SB>20-140</SB>can be made ≤3 ppm/°C by controlling the average crystal grain diameter relating to αμir to be ≤5 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sintered ferrite body having a small change in magnetic permeability over a wide temperature range and a small absolute value of a temperature coefficient.

  Until now, what was indicated by patent documents 1-3 as a Ni-Cu-Zn system ferrite material which shows a low temperature coefficient is known. In each of Patent Documents 1 to 3, a low temperature coefficient is realized by controlling the main composition and adding a predetermined amount of Bi or the like as a subcomponent.

Specifically, in Patent Document 1, the range of 46.0 to 49.0 mol% in terms of Fe ₂ O ₃ , the content of copper oxide in the range of 4.0 to 11.0 mol% in terms of CuO, zinc oxide In the range of 30.1 to 33.0 mol% in terms of ZnO and the remaining nickel oxide, and cobalt oxide as a subcomponent with respect to these main components is 0.005 to 0.03 in terms of CoO. In the range of wt%, Bismuth oxide in the range of 0.1 to 0.5 wt% in terms of Bi ₂ O ₃ , Silicon oxide in the range of 0.1 to 0.6 wt% in terms of SiO ₂ , Magnesium oxide in terms of MgO In a range of 0.05 to 1.0% by weight.
Range content of Patent Document 2 iron oxide is 40 to 46 mol% calculated as Fe ₂ O _3, ranges the content of zinc oxide is 25.1 to 30 mol% in terms of ZnO, the content of nickel oxide NiO In the range of 10 to 25 mol% in terms of conversion and the remaining copper oxide, bismuth oxide as a minor component with respect to these main components in the range of less than 2% by weight in terms of Bi ₂ O ₃ , and cobalt oxide in Co ₃ O It is contained in the range of 0.1% by weight or less in terms of ₄ .
In Patent Document 3, Ni—Cu—Zn ferrite is the main component, Nb is 0.2 to 0.8 wt% in terms of Nb ₂ O ₃ , Ta is 0.3 to 1.2 wt% in terms of Ta ₂ O ₅ , Mo is contained in the range of 0.15 to 1.35 wt% in terms of MoO ₃ .

Japanese Patent Laid-Open No. 2002-60224 JP 2001-348226 A JP-A-5-3112

By controlling the main component of the Ni—Cu—Zn-based ferrite material and including the subcomponents, in Patent Documents 1 and 2, the absolute value of the relative temperature coefficient of initial permeability (hereinafter referred to as αμir) is 5 ppm / ° C. Hereinafter, in Patent Document 3, the absolute value of αμir is 1.3 ppm / ° C. or less.
However, αμir in Patent Documents 1 and 2 is a value at 20 to 60 ° C., and αμir in Patent Document 3 is a value at −25 to 85 ° C. Therefore, a ferrite material having a small absolute value of αμir in a wider temperature range, for example, −40 to 140 ° C., is demanded.
The present invention has been made based on such a technical problem, and an object thereof is to provide a ferrite material having a small absolute value of αμir in a wide temperature range of −40 to 140 ° C.

Based on this object, the present inventors have solved the above problems by controlling the main component and subcomponents and making the crystal grain size of the sintered body fine. That is, the present invention is _{Fe 2 O 3: 45.5~48mol%,} CuO: 5~10mol%, ZnO: 26~30mol%, balance substantially cobalt oxide CoO terms as a sub-component relative to the main component of the NiO And a ferrite sintered body characterized by having an average crystal grain size of 5 μm or less. The absolute value of αμir can be reduced by controlling the main component within the above-described range and containing cobalt oxide at 0.005 to 0.045 wt% in terms of CoO.
In addition, by controlling the average crystal grain size correlated with αμir to 5 μm or less, _both the absolute value of αμir _{−40 to 20} and the absolute value of αμir _{20 to 140} can be set to 3 ppm / ° C. or less. Note that αμir -40 to ₂₀ and αμir 20 to ₁₄₀ are obtained according to the following.
_{αμir -40~20 = [(μi 20 -μi} -40) / μi -40 2] × [1 / (T 20 -T -40)]
_{αμir 20~140 = [(μi 140 -μi} 20) / μi 20 2] × [1 / (T 140 -T 20)]
μi ₋₄₀ : initial permeability at −40 ° C. μi ₂₀ : initial permeability at 20 ° C. μi ₁₄₀ : initial permeability at 140 ° C.

Further, according to the study by the present inventors, it is important to make the standard deviation of the crystal grain size 2 μm or less in order to reduce the absolute value of αμir.
The ferrite sintered body of the present invention also has characteristics that the quality factor (Q value) at 125 kHz is 170 or more and the initial permeability μi at 125 kHz is 300 or more. That is, according to the above-described approach of the present invention, the absolute value of αμir can be reduced in a wide temperature range of −40 to 140 ° C. without any loss of magnetic characteristics or the like.

The present invention _{further, Fe 2 O 3: 45.5~48mol%} , CuO: 5~10mol%, ZnO: 26~30mol%, the balance substantially of NiO, the average grain size of 5μm or less, and the crystal grain Provided is a ferrite sintered body characterized in that the standard deviation of the diameter is 2 μm or less.
This ferrite sintered body does not necessarily contain cobalt oxide, but the main component is controlled within the above range, the average crystal grain size is 5 μm or less, and the standard deviation of the crystal grain size is 2 μm or less. by, it can be less both 3 ppm / ° C. the absolute value of the absolute value and Arufamyuir _{20 to 140} of _αμir -40~20.
In the present invention, cobalt oxide can be contained in the range of 0.005 to 0.045 wt% in terms of CoO as an auxiliary component.

  According to the present invention, there is provided a ferrite sintered body having a high Q value and a small absolute value of αμir in a wide temperature range of −40 to 140 ° C., and further −40 to 160 ° C.

<Organization>
The ferrite sintered body of the present invention is characterized in that the average crystal grain size is 5 μm or less and the standard deviation of the crystal grain size is 2 μm or less.
In the present invention, the average crystal grain size is 5 μm or less because the correlation between αμir and the average crystal grain size is large, and when the average crystal grain size exceeds 5 μm, αμir (αμir _{−40 to 20} ) at −40 to 20 ° C. This is because the absolute value exceeds 3 ppm / ° C. On the other hand, as shown in Example 2 described later, αμir (αμir _{20 to 140} ) at 20 to 140 ° C. tends to decrease as the average crystal grain size decreases. Therefore, in the present invention, the average crystal grain size is 5 μm or less, preferably 2 to 5 μm. Thereby, both αμir at −40 to 20 ° C. (αμir −40 to ₂₀ ) and αμir at 20 to 140 ° C. (αμir _{20 to 140} ) are absolute values of 3 ppm / ° C. or less, further 2.5 ppm / ° C. or less, More desirably, it can be set to 2 ppm / ° C. or less.

In the present invention, the standard deviation is set to 2 μm or less because the standard deviation and αμir are also correlated. By the standard deviation and 2μm or less, to 3 ppm / ° C. or lower in absolute value of both αμir (αμir _20~140) in αμir (αμir _-40~20) and 20 to 140 ° C. at -40～20 ° C. Can do.
When the average crystal grain size is 5 μm or less, the standard deviation of the crystal grain size is desirably 2 μm or less. In this case, a desirable standard deviation is 1.9 μm or less, more desirably 1.5 μm or less. By setting the average crystal grain size to 5 μm or less and the standard deviation of crystal grain size to 1.5 μm or less, αμir (αμir _{-40 to 20} ) at −40 to 20 ° C. and αμir (αμir _{20 to} 140 at _{20 to} 140 ° C. ) Both in absolute value can be 2.0 ppm / ° C. or less.
Although the standard deviation depends to some extent on the average crystal grain size, the method described later, that is, control of media conditions during grinding, adjustment of grinding time, adjustment of throughput per unit time, control of firing conditions Etc. can be changed.

<Composition>
Hereinafter, the reasons for limiting the composition of the ferrite sintered body according to the present invention will be described.
When the content of Fe ₂ O ₃ constituting the main component of the ferrite sintered body of the present invention is less than 45.5 mol%, the Q value is low and the Curie point (hereinafter, Tc) is also low. On the other hand, if the content of Fe ₂ O ₃ exceeds 48 mol%, αμir, particularly αμir (αμir _{−40 to 20} ) at −40 to 20 ° C. increases, and the absolute value thereof exceeds 3 ppm / ° C. Accordingly, the present invention is a 45.5～48Mol% content of _Fe 2 _{O 3.} The desirable Fe ₂ O ₃ content is 45.7 to 47.5 mol%, and the more desirable Fe ₂ O ₃ content is 46.0 to 47.0 mol%.

When the content of CuO constituting the main component of the ferrite sintered body of the present invention is less than 5 mol%, the Q value is lowered and the anti-stress characteristic is increased. On the other hand, when the content of CuO exceeds 10 mol%, αμir, particularly αμir (αμir _{−40 to 20} ) at −40 to 20 ° C. increases. Therefore, in this invention, content of CuO shall be 5-10 mol%. The desirable CuO content is 5.5 to 10 mol%, and the more desirable CuO content is 6 to 9.5 mol%.

When the content of ZnO constituting the main component of the ferrite sintered body of the present invention is less than 26 mol%, αμir, particularly αμir (αμir _{−40 to 20} ) at −40 to 20 ° C. increases. On the other hand, when the ZnO content exceeds 30 mol%, Tc decreases. Therefore, in this invention, content of ZnO shall be 26-30 mol%. A desirable ZnO content is 26.5 to 29.5 mol%, and a more desirable ZnO content is 27 to 29 mol%.
The balance of the main component of the ferrite sintered body of the present invention is substantially NiO.

  The ferrite sintered body of the present invention contains 0.005 to 0.045 wt% of cobalt oxide in terms of CoO with respect to the above main component. CoO is an important component for obtaining a high Q value and for reducing the absolute value of αμir, and when it is less than 0.005 wt%, the Q value becomes low, and when it exceeds 0.045 wt%, αμir increases. . The desirable CoO content is 0.01 to 0.03 wt%, and the more desirable CoO content is 0.015 to 0.025 wt%.

The ferrite sintered body having the above composition has an initial permeability μi at 125 kHz of 300 or more, a Q value at 125 kHz of 170 or more, and αμir ₋₄₀ to ₂₀ and αμir ₂₀ to ₁₄₀ are as low as 3 ppm / ° C. or less. Indicates the value.
Incidentally, αμir is generally defined as follows.
αμir = [(μi ₂ −μi ₁ ) / μi ₁ ² ] × [1 / (T ₂ −T ₁ )]
μi ₁ : Initial permeability at temperature T ₁ μi ₂ : Initial permeability at temperature T ₂ The present invention aims to reduce the absolute value of αμir in the temperature range of −40 to 140 ° C. The ferrite sintered body of the present invention has a peak in μi (initial permeability) near room temperature. Therefore, when αμir is obtained with μi ₁ as the initial permeability of −40 ° C. and μi ₂ as the initial permeability of 140 ° C., even if the temperature coefficient of the initial permeability μi increases at the peak position, it is not reflected. There is a fear. Therefore, in the present invention, αμir is obtained by dividing into two temperature ranges of −40 to 20 ° C. and 20 ° C. to 140 ° C., and the absolute value of both is 3 ppm / ° C. or less.

Moreover, the ferrite sintered compact of this invention can make Tc (Curie temperature) 160 degreeC or more by employ | adopting the above composition. A high Tc is required to ensure use in a high temperature environment, and in the present invention, a Tc of 180 ° C. or higher, or 200 ° C. or higher can be obtained.
Furthermore, the ferrite sintered body of the present invention is also excellent in mechanical strength. Specifically, it has a three-point bending strength of 20 kgf / mm ² or more. The three-point bending strength is a value measured according to JIS R1601 using a square sample.

Furthermore, the ferrite sintered body of the present invention can make the absolute value of the antistress characteristic 5% or less. Here, the anti-stress characteristic refers to the degree of change in the inductance value of the ferrite sintered body with respect to the compressive stress. In a resin mold type inductor element, a ferrite sintered body is resin-molded, and compressive stress is applied to the ferrite sintered body when the resin is cured. Since the ferrite sintered body has an inductance value that changes according to the magnitude of the compressive stress, the resin-molded type inductance element is a ferrite sintered body that has little change in inductance with respect to the compressive stress and has excellent anti-stress. Is desired. The ferrite sintered body of the present invention having an anti-stress characteristic of 5% or less in absolute value can be used as a resin mold type ferrite sintered body for inductor elements in response to this requirement. In the ferrite sintered body of the present invention, the absolute value of the anti-stress characteristic can be 4% or less, and further 3% or less. A specific calculation method of the anti-stress characteristic is as follows.
After winding a wire around a square sample 20 times, a uniaxial compressive force is applied thereto at a constant speed, the inductance value at this time is continuously measured, and the inductance change rate is calculated from the obtained measurement value. At this time, the uniaxial compressive stress is 1 ton / cm ² and the inductance change rate is obtained by the following equation.
(L ₁ −L ₀ ) / L ₀ × 100 (%)
L ₁ : Inductance value when uniaxial compression force is applied L ₀ : Inductance value without application of uniaxial compression force

  Next, the suitable manufacturing method of the ferrite sintered compact by this invention is demonstrated in order of each process. As described above, the ferrite sintered body according to the present invention is characterized in that the average crystal grain size of the sintered body is 5 μm or less, and the standard deviation of the crystal grain size of the sintered body is 2 μm or less. . In order to obtain a ferrite sintered body having such a fine structure with little variation, for example, pulverization conditions after calcining, firing conditions, and the like may be controlled. These desirable conditions will be described in each step.

<Formulation, mixing process>
First, for example, an Fe ₂ O ₃ powder, a CuO powder, a ZnO powder, and a NiO powder are prepared as raw material powders that are main components. In addition to these main component powders, a CoO powder component is prepared. What is necessary is just to select suitably the particle size of each raw material powder to prepare in the range of 0.1-10 micrometers, desirably 0.1-5 micrometers. The prepared raw material powder is wet-mixed using, for example, a ball mill. The mixing depends on the operating conditions of the ball mill, but a uniform mixed state can be obtained if it is carried out for about 20 hours. The addition of CoO as a subcomponent is not limited to wet mixing, and the same effect can be obtained even when calcination of a calcined powder described later.

  In the present invention, not only the above-mentioned main component materials, but also a composite oxide powder containing two or more metals may be used as the main component materials. For example, a complex oxide powder containing Fe and Ni can be obtained by oxidizing and baking an aqueous solution containing iron chloride and Ni chloride. This powder and ZnO powder may be mixed and used as a main component raw material. In such a case, calcining described later is unnecessary.

<Calcination process>
After mixing the raw material powder, calcining is performed. The calcining may be performed at a holding temperature in the range of 750 to 900 ° C. and the atmosphere may be air. The holding time for calcining may be 2 to 4 hours.

<Crushing process>
The calcined powder is pulverized to an average particle size of about 0.5 to 2.0 [mu] m, preferably 0.5 to 1.0 [mu] m using, for example, a ball mill or an airflow pulverizer. As an index of the size of the pulverized powder, there is a specific surface area in addition to the average particle diameter, but the specific surface area may be 2.0 to 4.0 m ² / g, preferably 2.5 to 3.5 m ² / g. .
In order to obtain a sintered body having an average crystal grain size of 5 μm or less and a standard deviation of the crystal grain size of the sintered body of 2 μm or less, it is necessary to form a powder having a small particle size and a narrow particle size distribution. Therefore, it is desirable to obtain a powder having a small particle size and a narrow particle size distribution at the pulverization stage. For example, by controlling the media conditions, adjusting the grinding time, adjusting the throughput per unit time, and adjusting the slurry concentration in the case of wet grinding, obtain a powder with a small particle size and a narrow particle size distribution. Can do.
Specifically, when pulverization is performed using a ball mill, it is effective to control media conditions (for example, increase the amount of media) and to increase the pulverization time. Since the amount of media is difficult to be crushed when the amount of media is small, the amount of media is desirably 600 to 1800 g with respect to 200 g of the object to be processed. The grinding time may be set to such an extent that a predetermined specific surface area can be obtained.
In order to obtain a powder having a small particle size and a narrow particle size distribution, it is also effective to perform pulverization using an airflow pulverizer. The air pulverizer is desirably equipped with a classifier. By using a pulverizer equipped with a classifier, coarse powder can be removed or re-pulverized to obtain a desired particle size distribution. It is also effective to change the grinding rate.

  The process for obtaining a powder having a small particle size and a narrow particle size distribution is not limited to the pulverization process. For example, after the pulverization step, the pulverized powder obtained in the pulverization step may be subjected to an operation such as removing or re-pulverizing the coarse powder to obtain a powder having a narrow particle size distribution.

It is desirable that the pulverized powder composed of the main component and the subcomponent is granulated into granules in order to smoothly perform the subsequent molding process. By granulating into granules, it becomes easy to control the particle size distribution within a narrow range.
Granules can be obtained by adding a small amount of a suitable binder such as polyvinyl alcohol (PVA) to the pulverized powder, and spraying and drying it with a spray dryer. The particle size of the obtained granules is desirably about 60 to 200 μm.

The obtained granule is formed into a desired shape using, for example, a press having a mold having a predetermined shape, and this formed body is subjected to a firing step. The holding temperature in firing may be 960 to 1100 ° C, preferably 980 to 1060 ° C. When the firing temperature exceeds 1070 ° C., the grain growth is likely to proceed, so that it becomes difficult to make the average crystal grain size of the sintered body 5 μm or less. On the other hand, when the firing temperature is lower than 900 ° C., the density of the sintered body is lowered and the anti-stress characteristic is lowered, which is not desirable.
The firing time may be 1 to 4 hours. As the firing time becomes longer, grain growth proceeds and the crystal grain size becomes larger. As a result, the standard deviation of the crystal grain size also increases. Therefore, in order to make the average crystal grain size 5 μm or less, it is important to control the firing time as well as the firing temperature.
Note that the firing may be performed in the air.

Fe ₂ O ₃ powder, ZnO powder, NiO powder and CuO powder as the main component composition are final compositions (mol%) of Fe ₂ O ₃ : 46.3, NiO: 17.1, CuO: 8.0, ZnO: 28 0.6 (mol%), and 0.02 wt% of CoO was added to the main component composition.
Next, these raw materials were wet-mixed using a steel ball mill, and the obtained mixed powder was calcined at 900 ° C. for 2 hours. Using a steel ball mill, 200 g of this calcined powder was pulverized under various pulverization conditions shown in Table 1 to obtain four types of pulverized powder. Table 2 shows the specific surface area and average particle size of the pulverized powder obtained. In addition, the pulverized powder obtained below was appropriately classified as “type A pulverized powder (specific surface area: 2.86 m ² / g, average particle size: 0.813 μm)”, “type B pulverized powder (specific surface area: 2. 70 m ² / g, average particle size: 0.859 μm) ”,“ type C ground powder (specific surface area: 3.16 m ² / g, average particle size: 0.782 μm) ”,“ type D ground powder (ratio) Surface area: 2.56 m ² / g, average particle size: 0.895 μm) ”.

Next, an aqueous polyvinyl alcohol solution was added as a binder to the obtained pulverized powders of types A to D and granulated. Using the thus-obtained granules having an average particle size of 60 to 200 μm, a toroidal sample (outer diameter 20 mm, inner diameter 10 mm, height 5 mm) for electromagnetic property evaluation was obtained by press molding. In addition, it shape | molded so that a shaping | molding density might be 3.20Mg / m < ³ >.
The molded body was fired at each temperature shown in Table 1. 1-12 were obtained. Sample No. The average crystal grain size of 1 to 12 was obtained, and the standard deviation of the crystal grain size was obtained based on the result. The results are shown in Table 1. The crystal grain size of the sintered body here is a value obtained from the result of observing the cross section of the sintered body (surface including the axis of the magnetic orientation direction) and measuring the individual crystal grain size by image analysis. It is. Specifically, the cross section of the mirror-polished sintered body is observed with an optical microscope, and each particle is recognized. Then, the area of each particle is obtained by image processing and calculated as the diameter of a circle having the same area as that value. It is the value. Measurement was performed on 200 to 300 crystal grains per sample. The average crystal grain size was the average value of the crystal grain sizes of all measured particles.

After winding the wire 20 times on the obtained toroidal sample, the permeability at 125 kHz was measured with an impedance analyzer (Yokogawa Hewlett-Packard 4192A). Table 1 shows μi, αμir -40 to ₂₀ and αμir ₂₀ to 140 based on the measurement result. Note that FIG. 1 to 4 are graphs showing the relationship between the average grain size of sintered bodies and αμir ₋₄₀ to _20, and FIG. It is a graph which shows the relationship between the standard deviation of the crystal grain diameter in 1-4, and ( _alpha) microir _-40-20 .
Further, after winding the wire 20 times on the obtained toroidal sample, the R value at 125 kHz was measured with the impedance analyzer described above, and the Q value was obtained from the formula: R / 2πfL = 1 / Q. The results are shown in Table 1.

As shown in Table 1, even when pulverized powder having the same specific surface area and average particle size is used, the average crystal particle size and standard deviation of the sintered body are increased by increasing the firing temperature.
In addition, for example, sample No. Sample Nos. 1 to 4 and type D ground powders were used. Comparison with 9 to 12 reveals that the average crystal grain size and standard deviation of the sintered bodies obtained are different if the pulverization conditions are different even if the firing conditions are the same. Specifically, Sample No. using a pulverized powder of Type A was used. 1 to 4 and sample Nos. 1 and 4 using type B ground powder. By comparison with 5 and 6, it was confirmed that the smaller the pulverized powder particle size and the longer the pulverization time, the smaller the sintered body average crystal particle size and standard deviation. Sample No. 1-4 and Sample No. Comparison with 9 to 12 shows that when the amount of media is small, the average particle size of the pulverized powder is large even if the pulverization time is lengthened, and when this is fired, the average crystal particle size of the sintered body tends to increase. It was.

Here, as shown in FIG. In any of 1-4, αμir _-40-20 increases as the average crystal grain size increases. In Table 1, Sample No. with an average crystal grain size exceeding 5 μm. About 4, 11, and 12, ( _alpha ) microir (( _alpha ) micro- _40-20 ) in -40-20 _degreeC will exceed 3 ppm / _degreeC . On the other hand, according to the samples according to the present invention having an average crystal grain size of 5 μm or less (sample Nos. 1 to ₃ and 5 to 10), absolute values of both αμir _{−40 to 20} and αμir _{20 to 140} are 3 ppm / ° C. Can be obtained.

Next, focusing on the standard deviation and αμir, it can be seen that the standard deviation and αμir are also correlated as shown in FIG. Then, the sample standard deviation is less 2 [mu] m (sample Nanba1～3,5～10) can be obtained a value of 3 ppm / ° C. or lower in absolute value for both _αμir -40~20 and _αμir 20~140. On the other hand, in samples (sample Nos. 4, 11, and 12) having a standard deviation exceeding 2 μm, αμir ₋₄₀ to ₂₀ is large, and thus the temperature range in which a low αμir of 3 ppm / ° C. or less in absolute value can be achieved is narrow.
From the above results, it is possible to obtain a low temperature coefficient in a wide temperature range of −40 to 140 ° C. by setting the average crystal grain size to 5 μm or less and further to the standard deviation of 2 μm or less within the range recommended by the present invention. I was able to confirm that it was possible. The sample according to the present invention also has the characteristics that the initial permeability μi at a measurement frequency of 125 kHz is 300 or more and the Q value is 170 or more. Therefore, the method according to the present invention in which the average crystal grain size is 5 μm or less and the standard deviation is 2 μm or less does not adversely affect the magnetic permeability and the Q value.

Fe ₂ O ₃ powder, ZnO powder, NiO powder and CuO powder as the main component composition are weighed to the final composition (mol%) shown in Table 2, and CoO is shown in Table 2 for this main component composition. Only the amount (wt%) was added.
Next, these raw materials were wet-mixed using a steel ball mill, and the obtained mixed powder was calcined at 850 ° C. for 2 hours, and this calcined powder was mixed and ground in a steel ball mill. The obtained pulverized powder had an average particle size of 0.5 μm.

Subsequently, the obtained calcined powder was granulated by adding an aqueous polyvinyl alcohol solution as a binder. Using the granules having an average particle diameter of 70 μm thus obtained, a toroidal sample for evaluating electromagnetic properties (outer diameter 20 mm, inner diameter 10 mm, height 5 mm) and a prismatic sample for evaluating mechanical strength (width 5 mm, thickness) 4 mm in length and 50 mm in length) was obtained by press molding. In addition, it shape | molded so that a shaping | molding density might be 3.20Mg / m < ³ >. The compact was fired at 1020 ° C. for 2 hours in the air, and sample No. 13-33 were obtained.

The magnetic permeability at 125 kHz was measured for the obtained toroidal sample. This measurement was performed under the same conditions as in Example 1. Table 2 shows μi, αμir -40 to ₂₀ and αμir ₂₀ to 160 based on the measurement result.
Further, the Q value was obtained under the same conditions as in Example 1. Further, Tc was measured for the obtained toroidal sample. For the measurement of Tc, a thermal analyzer (TA7000 manufactured by Vacuum Riko Co., Ltd.) was used. In addition, the average crystal grain size and standard deviation of the sintered body were determined in the same procedure as in Example 1. These results are shown in Table 2.

  Next, the three-point bending strength and the anti-stress characteristic were measured using the obtained prism sample. The results are also shown in Table 2.

As shown in Table 2, the samples (Nos. 14-16, 19-22, 25-27, 30-32) having the composition of the present invention and having a sintered body average crystal grain size of 5 μm or less, Αμir at −40 to 20 ° C. and 20 to 160 ° C. is 3 ppm / ° C. or less, Q value is 170 or more, and Tc is 160 ° C. or more. In addition, these samples have a bending strength of 20 kgf / mm ² or more and an antistress property of 5% or less.

Based on the above, sample no. Referring to FIGS. 13 to 17, it is understood that the quality factor (Q value) is less than 170 when Fe ₂ O ₃ is as small as 45.4 mol%. Conversely, if Fe ₂ O ₃ increases to 48.1 mol%, αμir _-40 to 20 exceeds 3 ppm / ° C.
Sample No. Referring to 18 to 23, if ZnO is as low as 25.5 _mol %, αμir _-40 to 20 exceeds 3 ppm / ° C. Conversely, it can be seen that when the ZnO content is as large as 30.5 mol%, the Tc is as low as less than 160 ° C.
Furthermore, sample no. Referring to 24-28, it can be seen that when CuO is as low as 4.9 mol%, the Q value is as low as 170 and the anti-stress characteristic is reduced to -5.1%. On the other hand, when CuO increases to 11.0 mol%, αμir _-40 to 20 exceeds 3 ppm / ° C. and the Q value is less than 170.
Furthermore, sample no. When 29-33 are referred, Q value will show the low value of less than 170, without adding CoO. However, it can be seen that αμir ₋₄₀ to 20 exceeds 3 ppm / ° C. when the amount of CoO added is increased to 0.05 wt%.
As described above, according to the present invention that adopts the approach of controlling the main component and subcomponents and making the crystal grain size of the sintered body fine, a high Q value and a wide temperature range of −40 to 160 ° C. This makes it possible to reduce the absolute value of the temperature coefficient.

Sample No. It is a graph which shows the relationship between the sintered compact average crystal grain size of 1-4, and ( _alpha) microir _-40-20 . Sample No. It is a graph which shows the relationship between the standard deviation of the crystal grain diameter in 1-4, and ( _alpha) microir _-40-20 .

Claims (8)

_{Fe 2 O 3: 45.5~48mol%,} CuO: 5~10mol%, ZnO: 26~30mol%, as an auxiliary component with respect to the main component of the balance substantially being NiO cobalt oxide in terms of CoO 0.005 Contained in the range of 0.045 wt%,
A ferrite sintered body having an average crystal grain size of 5 μm or less.   The ferrite sintered body according to claim 1, wherein the standard deviation of the crystal grain size is 2 μm or less. 3. The ferrite sintered body according to claim 1, _wherein an absolute value of αμir −40 to ₂₀ and an absolute value of αμir 20 to ₄₀ are 3 ppm / ° C. or less.
_{However, αμir -40~20 = [(μi 20} -μi -40) / μi -40 2] × [1 / (T 20 -T -40)]
_{αμir 20~140 = [(μi 140 -μi} 20) / μi 20 2] × [1 / (T 140 -T 20)]
μi ₋₄₀ : initial permeability at −40 ° C. μi ₂₀ : initial permeability at 20 ° C. μi ₁₄₀ : initial permeability at 140 ° C.   The ferrite sintered body according to any one of claims 1 to 3, wherein a quality factor (Q value) at 125 kHz is 170 or more.   5. The ferrite sintered body according to claim 1, wherein initial permeability μi at 125 kHz is 300 or more. _{Fe 2 O 3: 45.5~48mol%,} CuO: 5~10mol%, ZnO: 26~30mol%, and the balance substantially NiO,
A ferrite sintered body having an average crystal grain size of 5 μm or less and a standard deviation of crystal grain size of 2 μm or less.   The ferrite sintered body according to claim 6, wherein cobalt oxide is contained as a subcomponent in a range of 0.005 to 0.045 wt% in terms of CoO. The ferrite sintered body according to claim 6 or 7, _wherein an absolute value of αμir -40 to ₂₀ and an absolute value of αμir 20 to ₁₄₀ are 3 ppm / ° C or less.
_{However, αμir -40~20 = [(μi 20} -μi -40) / μi -40 2] × [1 / (T 20 -T -40)]
_{αμir 20~140 = [(μi 140 -μi} 20) / μi 20 2] × [1 / (T 140 -T 20)]
μi ₋₄₀ : initial permeability at −40 ° C. μi ₂₀ : initial permeability at 20 ° C. μi ₁₄₀ : initial permeability at 140 ° C.

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