JP2917706B2 - Oxide magnetic material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inductance component,
The present invention relates to an oxide magnetic material used for a transformer core for a power supply or the like, and particularly to a low-loss MnZn-based or Mn-based ferrite magnetic material having excellent high-frequency characteristics.

[0002]

2. Description of the Related Art In recent years, with the development of electronics technology, devices have been miniaturized and densified. For example, magnetic materials used for transformer cores for switching power supplies and the like are also required to cope with high frequencies, and in particular, low magnetic loss at high frequencies is required to prevent heat generation when downsized. Have been.

For example, magnetic materials applied to magnetic core materials and the like are roughly classified into metal materials and oxide ferrite materials. Metal-based materials have the advantage of high saturation magnetic flux density and high magnetic permeability, but have an electrical resistivity of 10 ^-6 to 10 ^-4.
Since it is as low as Ω · cm, there is a disadvantage that magnetic loss due to eddy current increases at high frequencies. This disadvantage can be improved by reducing the thickness of the magnetic material.Thus, a metal-based material processed into a thin foil and rolled into a roll with an insulator in between has been made. There is a limit of about 10 μm, and there are problems that it is difficult to produce a complicated shape and the cost is high. Therefore, it can be used only up to a frequency band of about 100 kHz.

On the other hand, the saturation magnetic flux density of ferrite-based materials is as low as about 1/2 of that of metal-based materials. However, the electrical resistivity is 1 Ω · c in a commonly used MnZn-based material.
m, which is much higher than that of metallic materials.
By using additives such as aO and SiO ₂ , the electric resistivity can be further increased to about 10 to several hundreds Ω · cm, and the magnetic loss due to eddy current is relatively small up to high frequencies. It can be used without doing. In addition, there is an advantage that a product having a complicated shape can be easily formed and the cost is low. For this reason, for example, this ferrite-based material has been generally used as a transformer core material for a power supply at a switching frequency of 100 kHz or more.

[0005]

However, even with such a ferrite-based material, there is a problem that when the frequency is 500 kHz or more, the magnetic loss due to the eddy current increases and it cannot be used.

If the temperature coefficient of the magnetic loss is positive near room temperature, the transformer generates heat due to the magnetic loss during actual use, and thus the temperature rises. As the temperature rises, the magnetic loss further increases and the heat is generated. There is a danger of repeated runaway and thermal runaway. For this reason, it is required to have a temperature characteristic such that the temperature coefficient of magnetic loss near room temperature is negative and the magnetic loss is minimized at a temperature around 60 to 80 ° C. actually used.

However, there is no material having a sufficiently low magnetic loss and a material having a relatively low magnetic loss generally has a minimum magnetic loss temperature near room temperature and easily causes thermal runaway, while a minimum magnetic loss temperature is 60 ° C. or higher. However, such a material has a problem that the magnetic loss is extremely large. Therefore,
There has been a problem that a material having very low magnetic loss and good temperature characteristics has not been obtained until now.

An object of the present invention is to provide an oxide magnetic material having extremely low magnetic loss at high frequencies and excellent temperature characteristics in order to solve the above-mentioned problems of the prior art.

[0009]

In order to achieve the above object, the oxide magnetic material of the present invention has a main composition of Fe
₂ O ₃ is 62 mol% or more and 66 mol% or less, and MnO is 1 mol
4 mol% or more and 28 mol% or less, ZnO 10 mol
% Or more and 20 mol% or less, and Ca
O in the range of 0.05% by weight to 0.5% by weight and SiO
₂ is a sintered body containing at least 0.005% by weight or more and 0.2% by weight or less.

[0010]

In the present invention, the main composition of the MnZn-based ferrite is limited because it is necessary to reduce the absolute value of the magnetic loss and at the same time control the temperature characteristics of the magnetic loss.

The role of the auxiliary component is to mainly increase the electric resistance value and reduce the magnetic loss due to the eddy current within the composition range of the MnZn-based ferrite. The lower limit of the amount added is the minimum required for the effect of reducing the magnetic loss to be exhibited. On the other hand, the reason for setting the upper limit is that if the amount of addition is excessively increased, the magnetic permeability is lowered and the magnetic loss is increased.

These subcomponents are effective even if only one kind is added alone, but simultaneous addition of CaO and SiO ₂ is essential to obtain a sample with sufficiently low loss.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an oxide magnetic material of composite ferrite, particularly MnZn ferrite or Mn ferrite (both are collectively referred to as MnZn ferrite or MnZn ferrite unless otherwise specified).
Fe ₂ O ₃ as main composition 62 mol% or more and 66 mol%
In the following, MnO is not less than 14 mol% and not more than 28 mol%,
nO is contained in an amount of 10 mol% or more and 20 mol % or less, and CaO is added as an auxiliary component in an amount of 0.05 wt% or more and 0.5 wt% or less.
Or less, and a composition containing 0.005% by weight or more and 0.2% by weight or less of SiO ₂ .

In general, among the magnetic properties of ferrite, the saturation magnetic flux density, the Curie temperature, the minimum loss temperature, and the like depend on the main composition, while the magnetic permeability, residual magnetic flux density, coercive force,
It is said that magnetic loss and the like are affected by the main composition, but are characteristics governed by the fine structure. In addition, high-frequency, low-loss MnZn ferrite is required to have high saturation magnetic flux density, Curie temperature, minimum loss temperature, and high magnetic permeability ("Powder and Powder Metallurgy" Vol.
No. P191).

The saturation magnetic flux density increases to some extent with the amount of ZnO and increases with the amount of Fe ₂ O ₃ . However, Z
If the amount of nO is too large, the Curie temperature decreases, and Fe ₂
It is known that when the O ₃ amount is too large, the magnetic permeability and the specific resistance value decrease, and DA (disaccommodation), which is a phenomenon in which the magnetic permeability changes with time, is likely to occur. For this reason, the main composition of the low-loss MnZn ferrite is optimized to contain about 53 to 54 mol% of Fe ₂ O ₃ and about ₉ to 12 mol% of ZnO (“Electronic Ceramics” Winter 1985). P4
4). Most of the low-loss ferrites actually developed are within this range, and the reduction of the loss was mainly based on the study of additives and microstructure using the main composition in the vicinity.

On the other hand, the minimum temperature of the magnetic loss of the MnZn-based ferrite has been conventionally explained by the temperature characteristic of the magnetic permeability. That is, when the temperature change of the magnetic permeability of the MnZn-based ferrite is measured, two maxima generally appear. One is a local maximum just below the Curie temperature, which is called a primary peak due to the Hopkinson effect. The other is a maximum near room temperature and is called a secondary peak. It was said that at the temperature of this secondary peak, magnetic loss was minimized. This secondary peak coincides with the temperature of K ₁ = 0 where the sign of the magnetocrystalline anisotropy constant K ₁ changes from a negative value to a positive value as the temperature rises. Although K ₁ increases monotonically with increasing temperature, Fe ²⁺ has a positive K ₁ , so that Fe ²⁺
The amount of Fe increases (ie, the amount of Fe ₂ O ₃ increases)
The temperature of the secondary peak moves to a lower temperature. Therefore, when the amount of Fe ₂ O ₃ in the main composition is large, the minimum loss temperature becomes too low, so that the amount of Fe ₂ O ₃ is generally about 54 mol% or less.

However, the present inventors actually manufactured MnZn-based ferrites having different main composition ratios under the same additive conditions, and examined the effect of the main composition in detail. As a result, in a main composition having a very large Fe ₂ O ₃ excess of 62 mol% or more and 66 mol% or less, which is completely different from those conventionally used, the minimum magnetic loss temperature can be reduced by using a specific additive. It has been found that ferrite having a low magnetic loss can be obtained at a temperature of 60 ° C. or more and at a frequency of 100 kHz to several MHz.

Hitherto, it has been considered that in a main composition in which Fe ₂ O ₃ is extremely excessive, eddy current loss increases due to a low specific resistance value, so that it cannot be used at high frequencies. However, according to studies by the inventors, even in a main composition in which Fe ₂ O ₃ is extremely excessive, an effective auxiliary component is added in combination to increase the specific resistance without increasing the hysteresis loss. It became clear that the absolute value of the magnetic loss can be reduced. That is, by selecting a specific main composition and adding specific amounts of CaO and SiO ₂ thereto, a material having a low magnetic loss can be obtained.

The oxide magnetic material of the present invention has a main composition of Fe 2 O 3 of 62 mol% to 66 mol%, MnO of 14 mol% to 28 mol%,
O was contained 20 mol% hereinafter least 10 mol%, and 0.5 wt% 0.05 wt% or more of CaO as an auxiliary component less and SiO ₂ 0.005 wt% 0.2 wt%
Always include the following, further M _x O _z a 0.01 wt% to 0.5 wt% or less (, M _x O _z is ZrO _2, HfO _2,
Ta ₂ O ₅ , Cr ₂ O ₃ , MoO ₃ , WO ₃ , Al ₂ O ₃ , Ga
₂ O ₃ , In ₂ O ₃ , GeO ₂ , SnO ₂ , Sb ₂ O ₃ , Bi ₂
When the sintered body contains at least one or more kinds selected from O ₃ ), a magnetic material having more excellent temperature characteristics of magnetic loss and low magnetic loss can be obtained.

This M_xO_zAs two or more metal oxides
Using CaO and SiO_TwoMore than 4 types
When combined addition, M_xO_zOf one of the
Is less than 0.01% by weight,
_xO_zIf the total amount of all is 0.01 weight or more,
The effect of reducing the loss by the addition appears. Of course, multiple species
Kind of M_xO_zThere is no problem even if each is within the addition range
And CaO and SiO _TwoMagnetic loss compared to only case
Can be reduced. In particular, M_xO_zAs Zr
O_TwoAnd another type of metal oxide.
Is to reduce chipping and chipping of the sintered body while reducing the loss.
It is effective in preventing it. In addition, other than those given in the present invention
Additives such as TiO_Two, CoO, NiO, V_TwoO_Five, N
b_TwoO_FiveIt does not matter if the amount is not particularly large.
Absent.

However, CaO, SiO ₂ and M _x
Even if O _z is added in an appropriate amount, a sample with sufficiently low loss cannot be obtained if the main composition is different. Further, if the main composition is different, lowering of the loss due to the additive may not be recognized in some cases. The material with the lowest loss can be realized by simultaneously satisfying the conditions of the main composition and the subcomponent. In addition, as a result of investigations by the present inventors, it has become clear that the problem of DA, for example, when used as a transformer core of a power supply, does not adversely affect characteristics because the excitation current exceeds the initial permeability range.

The magnetic loss minimum temperature, K ₁ where the sign of the crystal magnetic anisotropy constant K ₁ is changed from a negative with increasing temperature to a positive value
= 0, the amount of Fe ²⁺ having a positive K ₁ increases (that is, when the amount of Fe ₂ O ₃ increases), the minimum loss temperature moves to a lower temperature side, and is considered to be lower than room temperature. I was However, when the amount of Fe ₂ O ₃ in the main composition becomes 61 mol% or more, K ₁ <0 again at room temperature (for example, Journal Off Physical Society, Vol. 18, p. 684- (K. Ohta: J. Phys. So
c. Japan 18,684 (1963))), the minimum loss temperature can be controlled to 40 to 60 ° C. or more even in the composition with an excessive amount of Fe ₂ O ₃ .

On the other hand, with respect to the reduction of loss by the additive,
By simultaneously adding aO and SiO ₂ and segregating them at the grain boundaries, it is possible to increase the electric resistance and reduce the eddy current loss. However, by using a third additive further selected, , The loss can be further reduced.

However, according to the study by the inventors,
It is important to precipitate the third additive at the grain boundary.
It is important. If a large amount of additives is used, the electrical resistance will always be high.
And the eddy current loss is reduced, but the additive ferrite
Conversely, the solid solution in the phase increases the hysteresis loss.
You. Therefore, the amount of additives should be as small as possible and
Low loss material can be obtained by uniform precipitation
You. That is, this M _xO_zConcentration of the grain boundary layer
By making it more than 5 times the internal concentration, further loss
Can be reduced.

Other characteristics required for low magnetic loss MnZn ferrite include a sintered body having a relative density of 4.6 g / c.
Desirably, it is at least m ³ . If the sintering density is low, the loss increases because the effective area decreases. In addition, when the sintering density is low, the atmosphere is easily affected by cooling during firing, and in particular, in a composition having a large amount of Fe ₂ O _3, it is difficult to obtain the original characteristics unless the atmosphere is precisely controlled. This causes a reduction in the yield during manufacturing. Also,
The electric resistivity is desirably a DC resistivity of about 200 to 2 kΩ · cm and an AC resistivity (1 MHz) of about 20 Ω · cm or more. The magnetic permeability and the electrical resistivity vary depending on the crystal grain size. If the grain size is too small, the magnetic permeability decreases, and if it is too large, the electrical resistance decreases. Therefore, the average crystal grain size is 1
0 μm or less is preferable, and about 2 to 5 μm is desirable.

The MnZn-based ferrite material of the present invention has a minimum magnetic loss temperature of 60 ° C. or more and exhibits an extremely low magnetic loss even when the measurement frequency is in the MHz band. Therefore,
A switching power supply using the oxide magnetic material of the present invention as a magnetic core and having a switching frequency of 100 kHz to 5 MHz is a preferable application because it is small in size, high in efficiency and low in risk of thermal runaway.

Hereinafter, the present invention will be described by way of examples, focusing on the case where a part of M _x O _z is used. However, as shown in Examples 5 and 6, other claims of the present invention will be described. Similar effects were also observed when the above-mentioned additives were used, albeit with varying degrees.

Example 1 Powders of α-Fe ₂ O ₃ , MnCO ₃ , and ZnO having a purity of 99.5% were used as starting materials.
These powders have a composition ratio of (Table 1) and a total weight of 3
Each was weighed so as to be 00 g, mixed and pulverized by a ball mill for 10 hours in a wet system, and dried. After calcining these mixed powders in air at 850 ° C. for 2 hours, CaO was reduced to 0.1.
1 wt%, as SiO ₂ is 0.02 wt%, C
aCO ₃ and SiO ₂ were added, wet-mixed and pulverized again by a ball mill for 10 hours, and dried to obtain a calcined powder.

A 10% by weight of a 5% by weight aqueous solution of polyvinyl alcohol was added to these calcined powders, and granulated by passing through a 30 # sieve. The granulated powder was formed into a uniaxial mold, and the formed body was binder-out at 500 ° C. for 1 hour in the air, and then fired under the following two firing conditions.

The firing conditions are as follows: a firing temperature of 1200 ° C.
The O ₂ atmosphere was controlled according to the equilibrium oxygen partial pressure of the ferrite at the time of raising the temperature and maintaining the maximum temperature, and the cooling was performed in an atmosphere of nitrogen. At this time, the sintering time and the pressure at the time of molding were set such that the average crystal grain size of the sintered body was about 3 to 5 μm and the density of the sintered body was approximately
At about 6 g / cm ^3, it was varied to fall within the scope of 4.5~4.7g / cm ^3.

The characteristics were measured by measuring the outer diameter of the obtained sintered compact by 2 mm.
A ring-shaped sample having a thickness of 0 mm, an inner diameter of 14 mm, and a thickness of 3 mm was cut out, and the magnetic loss at 1 MHz and 50 mT was determined to be 20
It measured between 20 degreeC between 120 degreeC-120 degreeC. The magnetic loss was measured by wrapping a single layer of insulating tape around a ring-shaped ferrite core and then wrapping a single layer of an insulated conductor with a wire diameter of 0.26 mm over the entire circumference, and measuring using an AC BH curve tracer. did. The results are shown in (Table 1).

[0032]

[Table 1]

[0033] As Table 1 Results from clear, with the effect of the main composition, F e ₂ O ₃ is more than 62 mol% 66m
ol or less, and ZnO within the range of 10 mol% or more and 20 mol% or less , the loss minimum temperature was found to be 60 ° C or more, and the loss was as low as about 600 kW / m ³ or less.

(Embodiment 2) In the same manner as in Embodiment 1,
(Table 2) The composition ratio is as follows: 0.1% by weight of CaO,
CaCO ₃ , SiO ₂ and Ta ₂ O ₅ were added so that O ₂ was 0.02% by weight and Ta ₂ O ₅ was 0.1% by weight, and the sintered body was fired under the same firing conditions as in Example 1. Produced. From the obtained sintered body, the temperature characteristics of magnetic loss were measured by the same method and conditions as in Example 1. The results are shown in (Table 2).

[0035]

[Table 2]

As is clear from the results shown in Table 2, as in Example 1, the content of Fe ₂ O ₃ was 62 mol% or more and 66 mol%.
% Or less, in the range ZnO following 10 mol% or more 20 mol%, the loss has a loss minimum temperature 60 ° C. over 20
Very low loss of about 0 kW / m ³ or less, at least 90 kW / m ³ . When this result is compared with Table 1 of Example 1, the magnetic loss is about 100 when Ta ₂ O ₅ is added in addition to CaO and SiO ₂ (Table 2), depending on the main composition.
It decreased by about kW / m ³ .

Next, when these samples were broken and their fractured surfaces were observed, all of them were broken at the grain boundaries, and the average crystal grain size was about 4 μm. Then, No. 5, 7, 11,
With respect to the samples 17 and 19, the distribution of the Ta element in the fracture surface was measured using SIMS (secondary ion mass spectrometer). First, the analysis range was narrowed down to a diameter of 3 μm, and several tens of points were analyzed for the same sample. As a result, the Ta concentration was slightly different depending on the analysis position. Therefore, the analysis range is set to 50 × 50μ
The average Ta concentration was determined as m, and the profile of the Ta element in the depth direction from the fracture surface was measured.
As a result, in each of the samples, the Ta concentration decreased as the depth became deeper from the fracture surface (that is, the grain boundary portion) (going into the inside of the particle), and became substantially constant from the depth of about several tens nm. Then, comparing the Ta concentration in the grain boundary portion and the Ta concentration inside the particle where the concentration became almost constant, the concentration in the grain boundary portion was about 10 times higher in all samples.

Example 3 In the same manner as in Example 1, the composition ratio was Fe ₂ O ₃ = 65 mol%, MnO = 17 mol.
%, ZnO = 18 mol%, and the total weight is 300 g.
Each powder was weighed so as to obtain a mixture, wet-mixed and pulverized for 10 hours by a ball mill, and dried. This mixed powder is
After calcination in air at 00 ° C. for 2 hours, CaO and SiO ₂
Was adjusted to the amount shown in (Table 3), CaCO ₃ and SiO ₂ were added thereto, and wet-mixed and pulverized again by a ball mill for 10 hours, followed by drying to obtain a calcined powder. From these calcined powders, sintered bodies were produced in the same manner as in the firing conditions of Example 1.

For these sintered bodies, the temperature dependence of the magnetic loss was measured by the same method and under the same conditions (1 MHz, 50 mT) as in Example 1. As a result, the magnetic loss of the sintered body showed a minimum value at 80 ° C. regardless of the amount of CaO and SiO ₂ . The minimum magnetic loss values are shown in Table 3 in units of kW / m ³ .

[0040]

[Table 3]

As is clear from Table 3, when only CaO or SiO ₂ is added alone, high magnetic loss is obtained.
≦ CaO ≦ 0.5% by weight, 0.005 ≦ SiO ₂ ≦ 0.
When it is within the range of 2% by weight, the magnetic loss is 300 kW.
/ M ³ and low magnetic loss.

Example 4 In the same manner as in Example 3, the composition ratio was Fe ₂ O ₃ = 65 mol%, MnO = 17 mol.
%, ZnO = 18 mol%, and ZrO ₂
ZrO ₂ , CaCO ₃ and SiO ₂ were added so that the amount of CaO and SiO ₂ was 5 wt% (Table 4), and a sintered body was produced under the firing conditions of Example 1. With respect to the ring-shaped sample cut out from the obtained sintered body, the temperature dependence of the magnetic loss was measured under the same conditions as in Example 3. As a result, a minimum value was obtained at 80 ° C. for both CaO and SiO ₂ amounts. This minimum magnetic loss value is expressed in units of kW / m ³ (Table 4).
It was shown to.

[0043]

[Table 4]

As is apparent from a comparison between (Table 3) and (Table 4) in Example 2, the C
For all combinations of aO and SiO ₂ amounts, Z
Those to which rO ₂ was added had lower magnetic loss. However, the magnetic loss is originally low, 0.05 ≦ CaO ≦
The addition of ZrO ₂ within the range of 0.5 wt% and 0.005 ≦ SiO ₂ ≦ 0.2 wt% was effective in view of the absolute value of the magnetic loss.

Example 5 As in Example 1, the composition ratio was Fe ₂ O ₃ = 65.5 mol% and MnO = 17.5 mol.
%, ZnO = 17 mol%, and the total weight is 300 g.
Each powder was weighed so as to obtain a mixture, mixed and pulverized by a ball mill for 10 hours in a wet system, and dried. After calcining the mixed powder in air at 800 ° C. for 2 hours, CaO was reduced to 0.1%.
Wt%, next SiO ₂ is 0.02 wt%, ZrO _2, H
fO ₂ , Ta ₂ O ₅ , Cr ₂ O ₃ , MoO ₃ , WO ₃ , Al ₂ O
₃ , Ga ₂ O ₃ , In ₂ O ₃ , GeO ₂ , SnO ₂ , Sb
CaCO is adjusted so that ₂ O ₃ and Bi ₂ O ₃ have the amounts shown in (Table 5).
₃ and sintered bodies to which respective metal oxides were added were produced under the firing conditions of Example 1.

The temperature dependence of the magnetic loss of the ring-shaped sample cut from the obtained sintered body was measured under the same conditions as in Example 1.
It showed a minimum value at 80 ° C. The minimum loss value is shown in Table 5 in units of kW / m ³ .

[0047]

[Table 5]

As is clear from Table 5, CaO and S
Compared with the addition of only iO ₂ , ZrO ₂ , HfO ₂ , T
_{a 2 O 5, Cr 2 O} 3, MoO 3, WO 3, Al 2 O 3, Ga 2
O ₃ , In ₂ O ₃ , GeO ₂ , SnO ₂ , Sb ₂ O ₃ , Bi ₂ O
_{In the case where 3} was added in combination, the magnetic loss was further reduced within a specific addition range, and the minimum loss value was GeO ₂ = 0.2% by weight.
The addition resulted in a very low loss of 100 kW / m ³ .

Next, among the samples using these subcomponents,
With respect to the sample having the lowest addition amount (0.1 or 0.2% by weight), the depth profile of each additional metal element from the fracture surface was measured in the same manner as in Example 2. As a result, in each of the samples, the concentration of the added metal decreased as it progressed from the grain boundary to the inside of the grain, and became substantially constant from the depth of about several tens nm. Comparing the grain boundary portion with the concentration inside the grain where the concentration became almost constant, the concentration at the grain boundary portion was about 10 to several tens times higher in all samples.

(Embodiment 7) In the same manner as in Embodiment 1, F
e_TwoO_Three, MnCO_Three, ZnO powders,
Powder with composition ratio Fe_TwoO_Three= 63 mol%, MnO = 2
0 mol%, ZnO = 17 mol%, and the total weight is
Each was weighed so as to become 300 g, and further,
0.1% by weight of CaO in the final sintered body, SiO
_TwoIs 0.02% by weight, Ta_TwoO_FiveBecomes 0.05% by weight
Like CaCO_ThreeAnd SiO_TwoAnd Ta _TwoO_FiveWeighed and added
The mixture was wet-pulverized for 10 hours by a ball mill and dried.
This mixed powder is emptied at 800 to 1200 ° C. for 2 hours.
After calcining in the air, again in a ball mill for 10 to 20 hours
During that time, the mixture was wet-mixed and pulverized and dried to obtain a calcined powder.

To this calcined powder, 10% by weight of a 5% by weight aqueous solution of polyvinyl alcohol was added, and the mixture was passed through a 30 # sieve, granulated, and uniaxially molded.
Firing was performed under the atmosphere conditions shown in Example 1 for a time to obtain a sintered body. In the same manner, a sample was prepared in which only Ta ₂ O _{5 was} added during pulverization after calcination. When the temperature dependence of the magnetic loss of the ring-shaped sample cut out from the obtained sintered body was measured in the same manner as in Example 1, the loss showed a minimum value at 80 ° C. in each of the samples. The average crystal grain size of the sintered body was measured by observing the fracture surface of the sintered body with an electron microscope. Further, in the same manner as in Example 2, the Ta concentration in the grain boundary layer and inside the grains was measured, and the ratio of the grain boundary concentration / the inside grain concentration was determined. The results are shown in (Table 6).

[0052]

[Table 6]

As is clear from Table 6, the magnetic loss can be further reduced by Ta ₂ O _{5 as} compared with the case where no additive is added.
When the concentration ratio a was 5 or less, the effect was greatly reduced. Sample 10 having a sintered body density of less than 4.5 g / cm ³
, The loss was slightly high even when the Ta concentration ratio was 5 or more.

Example 8 As in Example 7, the composition ratio was Fe ₂ O ₃ = 65 mol%, MnO = 22 mol%, Zn
O = 13 mol%, 0.1% by weight of CaO, Si
The sintered body to which CaCO ₃ , SiO ₂ and Ta ₂ O ₅ are added so that O ₂ is 0.02% by weight and Ta ₂ O ₅ is 0.05% by weight is fired at 1200 ° C. for 5 hours. It was fired in the atmosphere of Example 1 to obtain a sintered body. In the same manner, Ta ₂ O ₅
A sample was prepared in which only addition was performed during pulverization after calcination. For a ring-shaped sample cut out from the obtained sintered body, the temperature dependence of magnetic loss was measured in the same manner as in Example 1.
The loss showed a minimum value at 80 ° C. in all samples. The average crystal grain size of the sintered body was measured by observing the fracture surface of the sintered body with an electron microscope. Further, in the same manner as in Example 2, the Ta concentration in the grain boundary layer and inside the grains was measured, and the ratio of the grain boundary concentration / the inside grain concentration was determined. The results are shown in (Table 7).

[0055]

[Table 7]

(Table 7) As is clear from Table 7, the magnetic loss can be further reduced by Ta ₂ O _{5 as} compared with the case where no additive is added.
When the concentration ratio a was 5 or less, the effect was greatly reduced. Sample 10 having a sintered body density of less than 4.5 g / cm ³
, The loss was slightly high even when the Ta concentration ratio was 5 or more.

Example 9 In the same manner as in Example 2, the composition ratio was Fe ₂ O ₃ = 64 mol%, MnO = 21 mol.
%, ZnO = 15 mol%, CaO 0.1% by weight, SiO ₂ 0.02% by weight, GeO ₂ 0.05% by weight were added to prepare a calcined powder. A sintered body (a) was produced under the firing conditions.

Similarly, the main composition is Fe ₂ O ₃ = 64 mo.
1%, MnO = 16 mol%, ZnO = 21 mol%, calcined powder prepared by adding CaO at 0.1 wt%, SiO ₂ at 0.02 wt%, and GeO ₂ at 0.05 wt% Then, a sintered body (b) was produced under the firing conditions of Example 1.

Similarly, the main composition is Fe ₂ O ₃ = 52 mo.
1%, MnO = 38 mol%, ZnO = 10 mol%, 0.1% by weight of CaO, 0.02% by weight of SiO ₂ , and 0.05% by weight of GeO ₂ were added. The aggregate (c) was produced. The magnetic loss of these sintered bodies was measured by the same method and conditions as in Example 1.

The sintered body has a density of 4.63 g / cm ³ ,
With a minimum magnetic loss temperature at ℃, the magnetic loss value is 100 kW
/ m ³ is an ultra-low magnetic loss material of this newly developed product. Also sintered body
(b) is a density of 4.59 g / cm ^3, has a magnetic loss minimum temperature at 100 ° C., the magnetic loss values Ru 230kW / m ³ der.
Meanwhile sintered body (c) is a density of 4.55 g / cm ^3, the magnetic loss values have 60 ° C. magnetic loss minimum temperature Ah at 850kW / m ³
You.

For each of these three types of samples, the product of the magnetic flux density B and the frequency f at the minimum loss temperature,
The magnetic loss was measured under the condition that B · f = 50 (mT · MHz) was constant (under this condition, the core size was constant with the power transformer at the same output). The results are shown in (Table 8).

[0062]

[Table 8]

As is clear from Table 8, these sintered bodies have the minimum loss around 0.5 to 2 MHz. (a)
Comparing (b) and (c) , the sintered body (a) of the present invention is advantageous at 300 kHz or more. However, at 10 MHz,
The loss increases significantly and loses its advantage over other materials (eg, NiZn-based ferrites).

Next, an E-shaped core was cut out from each of these sintered bodies, and a forward-type switching power supply circuit was prototyped using the core, and the temperature rise corresponding to magnetic loss was evaluated. Under constant light load conditions, the temperature and the temperature rise of the magnetic core with respect to the magnetic core magnetic flux density were measured. The results are shown in (Table 9).

[0065]

[Table 9]

As is clear from Table 9, when the allowable temperature rise due to the core loss of the transformer is estimated at 25 ° C.,
It can be seen that the power supply using the sintered body (c) has a large temperature rise and cannot be used at a very high frequency. On the other hand, the power supply using the developed ferrite material (a) has a small temperature rise, and can be sufficiently used up to 2.2 MHz or more at 50 mT. This is because the material used has very low magnetic loss and good temperature characteristics. At higher frequencies, it is common to lower the magnetic flux density, so it is considered that up to 5 MHz can be used from the results in (Table 8). However, 2
Switching power supplies of MHz or higher are not realistic at present because the loss on the circuit side increases.

From the above results, the switching frequency using the developed ferrite material is 100 kHz to 2 MHz.
Power supplies generate less heat, are more efficient, and have less risk of thermal runaway. In particular, the characteristic becomes remarkable above 300 kHz, and if the loss on the power supply circuit side is reduced, it can be used up to 5 MHz.

[0068]

As described above, according to the present invention, as a main composition, Fe ₂ O ₃ is not less than 62 mol% and not more than 66 mol%.
nO is 14 mol% or more and 28 mol% or less, and ZnO is 1 mol% or less.
A sintered body containing 0 mol% to 20 mol% , and at least 0.05% to 0.5% by weight of CaO and 0.005% to 0.2% by weight of SiO ₂ as subcomponents Since it is an oxide magnetic material, there is an effect that the material has low magnetic loss and excellent temperature characteristics, which has not been achieved in the past. Further, when the oxide magnetic material of the present invention is applied to, for example, a magnetic core of a switching power supply, there is also an effect that low heat generation, high efficiency, and low risk of temperature runaway can be achieved.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Osamu Ishii 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-5-67513 (JP, A) JP-A-60-262404 (JP, A) JP-A-5-74621 (JP, A) JP-A-5-21223 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) H01F 1/34 C01G 49/00

Claims (3)

(57) [Claims] The main composition is as follows: 62 mol% ≦ Fe ₂ O ₃ ≦ 66 mol% 14 mol% ≦ MnO ≦ 28 mol% 10 mol% ≦ ZnO ≦ 20 mol% 0.05 wt% ≦ CaO ≦ 0. An oxide magnetic material characterized by being a sintered body containing at least 5% by weight 0.005% by weight ≦ SiO ₂ ≦ 0.2% by weight. 2. The main composition is 62 mol% ≦ Fe ₂ O ₃ ≦ 66 mol% 14 mol% ≦ MnO ≦ 28 mol% 10 mol% ≦ ZnO ≦ 20 mol% 0.05 wt% ≦ CaO ≦ 0. 5% by weight 0.005% by weight ≦ SiO ₂ ≦ 0.2% by weight, and 0.01 ≦ M _x O _z ≦ 0.5% by weight (where M _x O _z in the formula is ZrO ₂ , HfO ₂ , Ta
₂ O ₅ , Cr ₂ O ₃ , MoO ₃ , WO ₃ , Al ₂ O ₃ , Ga
₂ O ₃ , In ₂ O ₃ , GeO ₂ , SnO ₂ , Sb ₂ O ₃ , Bi ₂
Oxide magnetic material characterized by being a sintered body containing at least one of at least one selected from O3). 3. The oxide magnetic material according to claim 2, wherein the concentration of M _x O _{z in} the grain boundary layer portion is at least five times the concentration inside the grains.