JPH09219306A - Low loss oxide magnetic material and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide NiZn group ferrite of high resistance (specific resistance >=10<6> Ωcm) and a low loss if excited with a large current in a high frequency band of 2M to 10MHz. SOLUTION: A basical compound composition of this magnetic material is composed of Fe2 O3 : 48 to 51mol%, ZnO: 11 to 25mol% and NiO: 24 to 41mol%. Alternatively, the basical compound composition is composed of Fe2 O3 : 48 to 51mol%, ZnO: 11 to 25mol%, CuO: 8mol% and NiO: 16 to 41mol%. Further, a Mo oxide of 5000ppm or less by conversion into MoO3 is added thereto, mean crystal particle size is 1 to 3μm and also the burning density is 85 to 96% of theoretical density. A ZnO compounded amount in the basical compound composition is -1.7×f+30-2.0<=ZnO<=-1.7×f+30+2.0 (mol%) in response to drive frequency f(MHz) of a transformer, however it is more preferable that it is coordinated in the range of 2<=f<=10 (MHz) and 11<=ZnO<=25 (mol%).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low loss oxide magnetic material and a method for manufacturing the same, and more particularly to a main transformer for a switching power supply used in a high frequency band of 2 to 10 MHz, such as a chip transformer or a thin film transformer. In addition, it is a proposal for an oxide magnetic material having high resistance and low loss, which is preferably used for a component in which a winding and a magnetic material have an integrated structure.

[0002]

2. Description of the Related Art A switching power supply is generally used at a conversion frequency in the 100k to 200kHz band, and as a transformer material for such a switching power supply, conventionally,
Low-loss MnZn ferrite is used. However, with the reduction in size and weight of electronic devices, recently, there has been an increasing demand for oxide magnetic materials that exhibit low loss characteristics even in a higher frequency band.

In response to this demand, even in the conventional MnZn ferrite used for the above-mentioned applications, by devising the basic component composition, trace additives, pulverization method, firing method, etc.,
A material having a low loss and a desired temperature characteristic can be obtained up to a frequency band of about 2 MHz to 3 MHz. However, with conventional MnZn ferrites, 2M-3MHz
It has been difficult to stably obtain a material exhibiting a low loss characteristic even in a high frequency band exceeding 1.0.

Therefore, in the high frequency band exceeding 2 MHz to 3 MHz, NiZn type ferrite having excellent high frequency magnetic characteristics and high resistance has been attracting attention as the transformer material replacing the MnZn ferrite.

On the other hand, with the recent trend toward miniaturization of parts and automatic mounting, miniaturization of transformers into chips is progressing. In such a chip transformer, since the winding and the magnetic material are made into an integral structure, the magnetic material that has a high resistance is Ni.
Zn-based ferrite has already been used.

However, the NiZn type ferrite described above was developed for processing weak signals of the exciting current, and therefore, when excited with a large current like a transformer for a switching power supply, the hysteresis loss becomes large. There was a problem.

As described above, in the prior art, it was not possible to obtain a low-loss NiZn-based ferrite that suitably operates under high frequency and large current excitation. On the other hand, the inventors first
A high-frequency low-loss NiZn-based ferrite disclosed in JP-A-7-272917 has been proposed. However, the NiZn-based ferrite of this proposal has a target frequency of 1 MHz as shown in the embodiment of the proposal, and if it is used in a higher frequency band of about 2 M to 10 MHz, magnetic loss is significantly increased. There was a problem.

[0008]

As described above, the conventional NiZn type ferrite has a high resistance and exhibits magnetism up to a high frequency band, but has a problem that it causes a large magnetic loss under high frequency and large current excitation. there were.

The main object of the present invention is to solve the above problems of the prior art, that is, high resistance (specific resistance ≧ 10 ^6).
The purpose of the present invention is to provide a NiZn-based ferrite which has a low loss even when excited with a large current in a high frequency band of 2 MHz to 10 MHz. Another object of the present invention is NiZn having the above magnetic properties.
The purpose is to propose a method suitable for producing a system ferrite.

[0010]

As a result of intensive studies to achieve the above object, the inventors have developed the present invention having the following contents. That is, the present invention provides (1) basic component composition is _{Fe 2 O 3: 48~51 mol%} , ZnO: 11~25 m
ol% and NiO: 24-41%, and MoO ₃
The average crystal grain size is 1 to 3 μm, and the sintering density is the theoretical density
It is a low loss oxide magnetic material characterized by 85 to 96%.

(2) The basic component composition is Fe ₂ O ₃ : 48 to 51 mol%,
ZnO: 11-25 mol%, CuO: less than 8 mol% and NiO: 16-41
The average crystal grain size is 1 to 3μ, which is made by adding more than 5000ppm of Mo oxide in terms of MoO ₃ to the one consisting of mol%.
and a sintered density of 85 to 96% of the theoretical density, which is a low loss oxide magnetic material.

(3) In the low loss oxide magnetic material described in (1) and (2) above, the ZnO compounding amount in the basic component composition is -1.7 xf + 30- depending on the driving frequency f (MHz) of the transformer. 2.0 ≦ ZnO ≦ −1.7 × f + 30 + 2.0 (mol%) However, low loss oxide magnetic material characterized by being adjusted within the range of 2 ≦ f ≦ 10 (MHz) and 11 ≦ ZnO ≦ 25 (mol%) Is.

In the method for producing a low-loss oxide magnetic material according to the present invention, the oxide raw material which is a main component is weighed, mixed and calcined to obtain a calcined ferrite powder, which contains a sub-component. When the low-loss oxide magnetic material according to claim 1 or 2 is manufactured by adding and crushing, then granulating and shaping, and then firing, as the subcomponent,
Add 1000ppm or less of Mo oxide in terms of MoO ₃
It is characterized in that it is baked in the temperature range of 30 ° C.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Fe ₂ O ₃ constituting the basic component of the oxide magnetic material according to the present invention has a content of 48 to 51 mol.
%. The reason for limiting to this range is that when the Fe ₂ O ₃ content is less than 48 mol%, it is especially important from the viewpoint of safety when used in a magnetic core of a transformer, etc.
Regarding magnetic loss at 100 ° C, hysteresis loss cannot be reduced. On the other hand, the content of Fe ₂ O ₃ is 51 mol
%, The electrical resistance sharply decreases, the eddy current loss increases, and direct winding to the core, which is one of the advantages of NiZn ferrite, cannot be performed. The content of more preferred Fe ₂ O ₃ is from 48.5 to 50.0
It is mol%, and the most excellent low magnetic loss characteristics can be obtained in this range.

ZnO, which is a basic component of the oxide magnetic material according to the present invention, has a content of 11 to 25 mol%.
The reason for limiting this range is that if the ZnO content is less than 11 mol%, the hysteresis loss cannot be reduced, while if it exceeds 25 mol%, the high-frequency magnetic properties deteriorate and
This is because the residual loss at 0 ° C increases significantly (in particular,
It becomes remarkable above 4 MHz. ).

The more preferable ZnO content depends on the driving frequency of the transformer, and the higher the driving frequency, the more optimal the Zn content.
The range of O content decreases. With respect to this point, the inventors conducted experiments and obtained the following findings. That is, first, Fe ₂ O ₃ :
Constantly 49 mol%, ZnO: 10-27 mol% and the balance NiO were weighed in different composition ratios, wet-mixed and calcined at 850 ° C for 3 hours, and the obtained NiZn ferrite calcined powder had MoO ₃ : 3500ppm. Was added and wet pulverized, then PVA was used as a binder and granulated, and molded at a molding pressure of 1 ton / cm ² to obtain a toroidal shaped body having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 8 mm. Various types of NiZn ferrite sintered bodies were produced by firing the formed body in the air at 1100 ° C. for 3 hours. Then, with respect to the NiZn ferrite sintered body produced in this way, (3 MHz, 20 mT), (6 MHz, 10 mT), (10 MHz
An experiment was conducted to measure the core loss at z, 5mT). As a result, from the result shown in FIG. 1, the relationship between the driving frequency f (MHz) and the optimum ZnO content (mol%) is ZnO = −1.7 × f + 30 (mol%) (1) where 2 ≦ It can be expressed by f ≦ 10 (MHz) and 11 ≦ ZnO ≦ 25 (mol%). Further, since the high frequency magnetic loss depends on the sintering density, the crystal grain size, the crystal grain size distribution, the grain boundary structure, etc., the range of the optimal ZnO content is the optimal value ± 2.0 given by the above formula (1). It was found to have a width of (mol%). Therefore, for example, Zn when the drive frequency f is 3 MHz
O content is 22.9-25 mol% and driving frequency f is 6M
The ZnO content in the case of Hz is 17.8 to 21.8 mol%, and the ZnO content in the case of the driving frequency f of 10 MHz is 11 to 15 mol%.

The NiO constituting the basic component of the oxide magnetic material according to the present invention has a content of 24-41 mol%.
The reason for limiting this range is that when the NiO content is less than 24 mol%, the high-frequency magnetic properties deteriorate, and the residual loss increases at 100 ° C, while when it exceeds 41 mol%, the hysteresis loss increases. Because it will increase. The more preferable NiO content depends on the drive frequency of the transformer, and as the drive frequency increases, the range of the optimum NiO content increases as the optimum ZnO content decreases. For example, drive frequency f is 3MHz
In the case of, the preferable NiO content is 26 to 29 mol%, and when the driving frequency f is 10 MHz, the preferable NiO content is 34 to 41 m.
ol%.

In the present invention, in order to reduce the firing temperature (accelerate the sintering) and reduce the raw material cost, a part of the NiO component is less than 8 mol%, more preferably 6 mol% or less.
It can be replaced by the CuO component. The reason why the substitution amount of the NiO component by the CuO component is less than 8 mol% is that the substitution of the CuO component by 8 mol% or more significantly changes the magnetocrystalline anisotropy constant and the magnetostriction constant in the crystal grain, or the firing temperature. Is decreased, and the grain boundary stress relaxation effect due to the addition of MoO ₃ as described later cannot be obtained, so that the high frequency magnetic loss is significantly deteriorated.

In the present invention, in order to obtain an oxide magnetic material with low loss, in addition to the basic component of the NiZn type ferrite described above, a Mo oxide is further added as a secondary component. This Mo oxide contains 5000 ppm or less in terms of MoO ₃ , more preferably 1500 to 4500 ppm in MoO ₃ , and more preferably MoO _3.
Includes over 3000 to 4000 ppm in conversion. The reason for this is that if the Mo oxide content exceeds 5000 ppm, abnormal grain growth of crystal grains tends to occur, and the loss reduction effect cannot be obtained.

In the present invention, in order to more effectively bring out the loss improving effect by the addition of MoO ₃ , it is necessary to set the average crystal grain size in the range of 1 to 3 μm. The reason is that if the average crystal grain size is smaller than 1 μm, the hysteresis loss increases, while if the average crystal grain size is larger than 3 μm, the high frequency magnetic properties deteriorate and the residual loss at 100 ° C. increases. is there. Further, the sintered density is preferably in the range of 85 to 96% of the theoretical density. The reason for this is that if the sintered density is less than 85% of the theoretical density, the loss cannot be reduced because the effective magnetic material occupancy rate is low.
This is because at a high density of more than 96%, the residual compressive stress at the grain boundary becomes high, so that the loss cannot be reduced.

The loss improving mechanism of the NiZn type ferrite by the addition of MoO ₃ described above can be explained as follows according to the study by the inventors. That is, MoO ₃ having a boiling point in the firing temperature range
By adding (boiling point of single substance: 1257 ° C), part of MoO ₃ is evaporated from the grain boundaries during firing, and the compressive stress remaining at the grain boundaries is relaxed, and hysteresis loss is reduced. I can guess. MoO ₃ is a low-melting oxide (melting point of a single substance: 795 ° C), which produces a liquid phase during the temperature rising process during firing and promotes densification of the sintered body, and the crystal grain size during the holding process. Contribute to the homogenization of. As a result, it can be presumed that the ratio of crystal grains of less than 1 μm that causes the hysteresis loss and the ratio of crystal grains of more than 3 μm that causes the residual loss are reduced, and the high frequency magnetic loss is reduced. Therefore, the crystal grain size needs to be 1 to 3 μm on average.

Thus, the oxide magnetic material of the present invention is Mo
A low loss is realized by utilizing the thermal properties of O ₃ .
Therefore, in the method for producing an oxide magnetic material according to the present invention, it is desirable to maintain the holding temperature in the firing process in the range of 1000 to 1130 ° C. The reason for this is that below 1000 ° C, the sintered density and crystal grain size become small and the hysteresis loss increases, while above 1130 ° C, the sintered density and crystal grain size become large and the residual loss increases. At the same time, since the densification of the sintered body proceeds too much, the evaporation of MoO ₃ is suppressed, and the hysteresis loss reducing effect cannot be obtained.

According to the oxide magnetic material of the present invention as described above, a NiZn ferrite having a specific resistance ≧ 10 ⁶ Ωcm and a low loss even when excited with a large current in a high frequency band of 2 M to 10 MHz is obtained. be able to.

[0024]

【Example】

(Example 1) (1) Fe ₂ O ₃ , ZnO and NiO, which are main oxide raw materials, were weighed and wet-mixed so that the component composition ratios shown in Table 1 were obtained.
It was calcined at 850 ° C for 3 hours to obtain a calcined powder of NiZn ferrite. (2) Next, after adding 3000 ppm of MoO ₃ to the above calcined powder, wet pulverizing and drying, and then adding PVA as a binder to granulate, and then molding at a molding pressure of 1 ton / cm ^2. A toroidal shaped body having an outer diameter of 36 mm, an inner diameter of 24 mm and a height of 8 mm was obtained. (3) Then, the obtained compact was fired in the air at 1100 ° C. for 3 hours to obtain a NiZn ferrite.

With respect to the NiZn-based ferrite thus obtained, the sintering density, the average crystal grain size, 3 MHz, 20 mT, and 100 ° C.
The core loss under the above conditions and the specific resistance under the conditions of room temperature and 10 V application were measured. Table 1 shows the results. In addition, as a comparative example shown in Table 1, NiZn-based ferrite having a composition deviating from the scope of the present invention was produced by the same method, and the same evaluation was performed.

As is clear from the results shown in Table 1, within the range of the component composition of the present invention, the specific resistance is> 10 ⁶ Ω.
It was found that a NiZn-based ferrite having a cm and a core loss of <1200 kW / m ³ can be obtained.

[0027]

[Table 1] * MoO ₃ addition amount: 3000ppm, firing temperature: 1100 ℃ Specific resistance measurement condition: room temperature, 10V applied core loss measurement condition: 3MHz, 20mT, 100 ℃

Example 2 (1) Fe ₂ O ₃ , ZnO and NiO, which are the main oxide raw materials, were weighed and wet mixed so that the composition ratio shown in Table 2 was obtained.
It was calcined at 950 ° C for 2 hours to obtain a calcined powder of NiZn ferrite. (2) Next, after adding 3500 ppm of MoO ₃ to the above calcined powder, wet pulverizing and drying, and then adding PVA as a binder to granulate, and then molding at a molding pressure of 1 ton / cm ^2. A toroidal shaped body having an outer diameter of 36 mm, an inner diameter of 24 mm and a height of 8 mm was obtained. (3) Then, the obtained molded body was fired in the air at 1050 ° C. for 3 hours to obtain a Ni—Zn ferrite.

With respect to the NiZn-based ferrite thus obtained, the sintering density, the average crystal grain size, 6 MHz, 10 mT, and 100 ° C.
The core loss under the above conditions and the specific resistance under the conditions of room temperature and 10 V application were measured. Table 2 shows the results.

As is clear from the results shown in Table 2, within the range of the component composition according to the present invention, the specific resistance is> 10 ⁶ Ω.
cm, and a core loss <1200 kW / m ³ of NiZn-based ferrite was obtained. In particular, core loss <1100 kW / m ³ was obtained within the range of the ZnO amount according to the driving frequency described in claim 3,
It turned out that the effect was remarkable.

[0031]

[Table 2] * MoO ₃ addition amount: 3500ppm, firing temperature: 1050 ℃ Specific resistance measurement condition: room temperature, 10V applied core loss measurement condition: 6MHz, 10mT, 100 ℃

Example 3 (1) Fe ₂ O ₃ , ZnO and NiO, which are main oxide raw materials, were weighed and wet-mixed so that the component composition ratios shown in Table 3 were obtained.
It was calcined at 925 ° C for 2 hours to obtain a calcined powder of NiZn ferrite. (2) Next, after adding 4000 ppm of MoO ₃ to the above calcined powder, wet pulverizing and drying, and then adding PVA as a binder to granulate, and then molding at a molding pressure of 1 ton / cm ^2. A toroidal shaped body having an outer diameter of 36 mm, an inner diameter of 24 mm and a height of 8 mm was obtained. (3) Then, the obtained compact was fired in the air at 1080 ° C. for 3 hours to obtain a NiZn ferrite.

With respect to the NiZn-based ferrite thus obtained, the sintering density, the average crystal grain size, 10 MHz, 5 mT and 100 ° C.
The core loss under the above conditions and the specific resistance under the conditions of room temperature and 10 V application were measured. Table 3 shows the results. In addition, as a comparative example shown in Table 3, NiZn-based ferrite having a composition deviating from the scope of the present invention was produced by the same method, and the same evaluation was performed.

As is clear from the results shown in Table 3, within the range of the composition of the present invention, the specific resistance is> 10 ⁶ Ω.
cm, and a core loss <450 kW / m ³ of NiZn-based ferrite was obtained, in particular according to the driving frequency described in claim 3.
Within the range of ZnO amount, core loss <400 kW / m ³ was obtained, and the effect was particularly remarkable.

[0035]

[Table 3] * MoO ₃ addition amount: 4000ppm, firing temperature: 1080 ℃ Core loss measurement condition: 10MHz, 5mT, 100 ℃

Example 4 With respect to the composition of No. 1 in Table 1, NiZn-based ferrites obtained by firing at different firing temperatures were tested for sintering density, average crystal grain size, 3 MHz, 20 mT, 100 ° C. The core loss under the conditions and the specific resistance under the conditions of room temperature and 10 V application were measured. The results are shown in Table 4. As is clear from the results shown in Table 4, it was found that the loss was low within the ranges of the sintered density and the average crystal grain size according to the present invention.

[0037]

[Table 4] * MoO ₃ addition amount: 3000ppm Core loss measurement condition: 3MHz, 20mT, 100 ° C

Example 5 With respect to the composition of No. 3 in Table 1, a part of NiO was replaced with CuO, and a NiZn type ferrite obtained by the same method as in Example 1 was sintered density. The average crystal grain size, the core loss under the conditions of 3 MHz, 20 mT and 100 ° C., and the specific resistance under the conditions of room temperature and 10 V application were measured. The results are shown in Table 5. As is clear from the results shown in Table 5, it was found that the substitution amount of CuO according to the present invention resulted in low loss.

[0039]

[Table 5] * MoO ₃ addition amount: 3000ppm, firing temperature: 1100 ℃ Core loss measurement condition: 3MHz, 20mT, 100 ℃

(Example 6) Other than changing the amount of MoO ₃ added to the obtained calcined powder by calcining the main oxide raw material so as to have the same composition as No. 1 in Table 3. A NiZn-based ferrite was obtained in the same manner as in Example 3.

With respect to the NiZn-based ferrite thus obtained, the sintered density, the average crystal grain size, 10 MHz, 5 mT, and 100 ° C.
The core loss under the above conditions and the specific resistance under the conditions of room temperature and 10 V application were measured. Table 6 shows the results. As is clear from the results shown in Table 6, it was found that the CuO substitution amount according to the present invention resulted in low loss.

[0042]

[Table 6] * Baking temperature: 1080 ℃ Core loss measurement condition: 10MHz, 5mT, 100 ℃

In each of the above-mentioned examples, the addition of MoO ₃ was carried out before the pulverization. However, if the calcination temperature is in the temperature range of 1000 ° C. or less, the addition of MoO ₃ together with other components before the calcination is similar. The effect is obtained.

[0044]

As described above, according to the oxide magnetic material of the present invention, high resistance (specific resistance ≧ 10 ⁶ Ωcm) and 2
Low loss even when excited with a large current in the high frequency band of M to 10 MHz
NiZn type ferrite can be obtained. Therefore, the oxide magnetic material of the present invention exhibits excellent characteristics for applications under high frequency and large current excitation such as a transformer for a switching power supply used at 2M to 10MHz, and particularly, for a chip transformer and a thin film transformer. It exhibits excellent characteristics as a core material of a transformer having a structure in which a winding and a magnetic material are integrated.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between ZnO content and core loss.

Claims (4)

[Claims] 1. The basic component composition is Fe ₂ O ₃ : 48 to 51 mol%, Zn
O: 11 to 25 mol% and NiO: 24 to 41%, further added with 5000 ppm or less of Mo oxide in terms of MoO ₃ , the average crystal grain size is 1 to 3 μm, and the calcination thereof is performed. A low-loss oxide magnetic material having a binding density of 85 to 96% of the theoretical density. 2. The basic component composition is Fe ₂ O ₃ : 48 to 51 mol%, Zn
O: 11-25 mol%, CuO: less than 8 mol% and NiO: 16
〜41 mol% and further 5000p in terms of MoO ₃
The average crystal grain size is 1 to 1 made by adding Mo oxide of pm or less.
A low-loss oxide magnetic material having a 3 μm and a sintered density of 85 to 96% of the theoretical density. 3. The amount of ZnO compounded in the basic composition is −1.7 × f + 30−2.0 ≦ ZnO ≦ −1.7 × f + 30 + 2.0 (mol%), where 2 ≦ f, depending on the driving frequency f (MHz) of the transformer. 3. The low loss oxide magnetic material according to claim 1, wherein the range is ≤10 (MHz) and 11≤ZnO≤25 (mol%). 4. An oxide raw material, which is a main component, is weighed, mixed, and calcined to obtain a calcined ferrite powder. By doing so, in producing the low-loss oxide magnetic material according to any one of claims 1 to 3, as the above-mentioned auxiliary component, 5000 ppm or less of Mo oxide in terms of MoO ₃ is added, and 1000 to 1130 ° C. A method for producing a low-loss oxide magnetic material, which comprises firing in the temperature range of 1.