JPH11307336A - Manufacture of soft magnetic ferrite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the drop of magnetic permeability in a high frequency area, by heat-treating spinel-type ferrite containing at least nickel oxide, and containing at least one type of Co, Ba and Sr in a magnetic field. SOLUTION: At least one type of Co, Ba and Sr is added to a temporarily baked object containing at least nickel oxide and it is baked. Then, spinel-type ferrite is formed. At that time, the content of CO, Ba and Sr is reduced to CoO, BaFe12 O19 and SrFe12 O19 and about 0.1-about 10 weight % in total is obtained. Spinel-type ferrite is heat-treated in a magnetic field and a face (111) is preferentially oriented. Spinel-type ferrite contains zinc oxide. The drop of magnetic permeability in a high frequency area is improved, the use limit frequency of ferrite containing nickel is extended and the use of ferrite at about 100 MHz is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a soft magnetic ferrite for high frequency.

[0002]

2. Description of the Related Art Ferrite is suitable for high frequency magnetic cores because eddy current loss is significantly smaller than that of metal. However, the limit frequency (Snoek
When this limit frequency is exceeded, the magnetic permeability decreases rapidly and the loss increases sharply, making it unusable. As the high-frequency ferrite, Ni-based spinel type ferrite such as Ni-Zn ferrite is often used, and in particular, Ni-Zn ferrite is frequently used because of its relatively high magnetic permeability. However, Ni-Z
The limit frequency of n-ferrite is less than 100 MHz, and it is desired to be able to use it at a higher frequency with the recent increase in the frequency used in electric and electronic devices.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide Ni
The purpose is to improve the critical frequency of the spinel-type ferrite, and in particular, to make Ni-Zn ferrite usable in a high frequency region of 100 MHz or more.

[0004]

The above object is achieved by the following (1).
This is achieved by any one of the above configurations (5) to (5). (1) Co, Ba containing at least nickel oxide
A method for producing a soft magnetic ferrite, comprising a step of heat-treating a spinel ferrite containing at least one of Sr and Sr in a magnetic field. (2) The spinel-type ferrite contains at least one of Co, Ba and Sr as CoO and BaFe, respectively.
Converted to ₁₂ O ₁₉ and SrFe ₁₂ O ₁₉ ,
The method for producing a soft magnetic ferrite according to the above (1) containing 10% by weight. (3) The spinel-type ferrite is produced by adding at least one of cobalt oxide, Ba ferrite, and Sr ferrite to a calcined product containing at least nickel oxide, followed by firing.
Or (2) the method for producing a soft magnetic ferrite. (4) The method for producing a soft magnetic ferrite according to any one of (1) to (3), wherein the (111) plane is preferentially oriented by heat treatment in a magnetic field. (5) The method for producing a soft magnetic ferrite according to any one of (1) to (4), wherein the spinel-type ferrite contains zinc oxide.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a heat treatment is performed in a magnetic field on a spinel ferrite containing at least nickel oxide and containing at least one of Co, Ba and Sr. By the heat treatment in this magnetic field, the drop in the magnetic permeability in a high-frequency range is improved and the frequency characteristics are improved. For example, in the case of Ni-Zn ferrite, a practically sufficient magnetic permeability is obtained at 100 MHz. In addition, in the case of Ni—Zn ferrite, a magnetic permeability of about 50 can be obtained at 100 MHz without heat treatment in a magnetic field by adding CoO. In this case, magnetic resonance occurs near 100 MHz and the magnetic permeability becomes unstable. Therefore, it cannot be put to practical use. On the other hand, when the present invention is applied to Ni—Zn ferrite, such a problem does not occur because the magnetic permeability is substantially constant even near 100 MHz.

The specific conditions for the heat treatment in a magnetic field may be appropriately determined according to the composition of the ferrite and the like.
The magnetic field strength is preferably at least 10 Oe, more preferably 1 kO
e or more, and the ultimate temperature is preferably 300 ° C. or more, more preferably 500 ° C. or more. If the magnetic field strength is too low or the temperature reached is too low, the effect of the heat treatment in the magnetic field becomes insufficient. Further, the time for maintaining the above-mentioned temperature is not particularly limited, and may be appropriately determined according to the size of the ferrite so that the entire ferrite of the object to be heated has a uniform temperature, but is usually 1 minute to 5 hours. It is preferable to set the degree. The cooling rate is preferably 30 to 200 ° C.
/ Hour, more preferably 50 to 100 ° C / hour. The effect of the present invention is realized by cooling while applying a magnetic field, whereby the magnetic ions in the ferrite are rearranged while thermally oscillating.If the cooling rate is too high, the time available for rearrangement is short. And a sufficient effect cannot be obtained. On the other hand, if the cooling rate is too slow, the thermal decomposition of ferrite may be promoted, and the treatment takes a long time to lower the efficiency, which is not preferable. Although there is no particular upper limit on the magnetic field strength used in the present invention, the upper limit is usually 100 kOe in current magnetic field generators that can be used for mass production.
It is about. In addition, the ultimate temperature is usually preferably 600 ° C. or lower. If the attained temperature is too high, ferrite is thermally decomposed and the possibility of deteriorating magnetic properties increases.
The heat treatment is preferably performed in the air or in an inert atmosphere such as nitrogen or argon.

It is considered that the improvement of the frequency characteristic of the magnetic permeability by the heat treatment in a magnetic field is due to the provision of uniaxial anisotropy. For example, in the analysis by X-ray diffraction, it can be confirmed that the (111) plane is preferentially oriented by the heat treatment in the magnetic field.

In the spinel type ferrite of the present invention,
The contents of Co, Ba and Sr are respectively CoO,
The total amount is preferably 0.1 to 10% by weight in terms of BaFe ₁₂ O ₁₉ and SrFe ₁₂ O ₁₉ , and 0.5 to 8% by weight.
More preferably, it is% by weight. If the content of these elements is too small, the effect of the present invention will be insufficient, and if the content is too large, the magnetic permeability will decrease.

In order to include Co, Ba and Sr in the spinel ferrite, a compound of these elements (hereinafter referred to as an additive compound) is added in the process of producing the spinel ferrite. As the additive compound, an oxide is preferable, and in particular, cobalt oxide, Ba ferrite and S
r Ferrite is preferred. By using these oxides, the effects of the present invention are significantly improved. The stoichiometric composition of cobalt oxide is CoO, the Ba ferrite is BaFe ₁₂ O ₁₉ , and the Sr ferrite is SrFe ₁₂ O _19, but the composition of the additive compound may deviate from the stoichiometric composition.

The spinel-type ferrite to which the present invention is applied contains at least nickel oxide. Such spinel ferrites include Ni ferrite, Ni-Zn ferrite, Ni-Cu ferrite, and N
i-Cu-Zn ferrite and the like are preferable, and among these, those containing zinc oxide, particularly Ni-Zn ferrite, are preferable. When the present invention is applied, the specific main composition of each ferrite is not particularly limited, and may be appropriately selected from a commonly used composition range. For example, Ni-Zn
The main composition of the ferrite is usually about 45～55Mol% in iron oxide in terms of Fe ₂ O _3, zinc oxide in terms of ZnO 10
~ 35mol%, nickel oxide is 15 ~
It is about 35 mol%. In addition, various subcomponents are added to each ferrite in order to improve the properties, and the present invention may also include various conventionally known subcomponents, and may also include unavoidable impurities that are usually included. . For example,
Examples of subcomponents or impurities in the Ni-Zn ferrite include calcium oxide, bismuth oxide, aluminum oxide, silicon oxide, and chromium oxide.

The average crystal grain size of the spinel-type ferrite produced according to the present invention is not particularly limited, and Co, Ba, S
It may be equivalent to the case where r is not added, for example, about 1 to 30 μm. Note that even if the manufacturing conditions are almost the same,
The crystal grain size may be affected by the addition of o, Ba, and Sr. For example, when CoO is added to Ni-Zn ferrite, when the addition amount is about 5% by weight, the crystal grain size becomes larger than when it is not added, but the addition amount is 10% by weight.
When the amount is about 5%, the crystal grain size becomes smaller than when the addition amount is 5% by weight. The reason why grain growth is suppressed in this way is that C
It is considered that when oO exceeds the allowable solid solution amount, segregation at crystal grain boundaries is likely to occur.

Next, a specific flow of the manufacturing method of the present invention will be described.

First, the main component materials are mixed so as to obtain a predetermined composition after firing. As a main component material, for example, in the case of Ni—Zn ferrite, iron oxide (Fe
₂ O ₃ ) powder, nickel oxide (NiO) powder and zinc oxide (ZnO) powder are used. In addition to these oxides,
Compounds that become oxides by firing, such as carbonates, hydroxides, and nitrates, can also be used. It is preferable to use a wet mixing method for the mixing.

Next, the mixed raw materials are calcined. In calcination, various conditions such as temperature and atmosphere may be selected to be optimal according to the main composition. For example, Ni-Zn ferrite may be calcined at about 800 to 1200 ° C. for about 1 to 10 hours in air or an atmosphere in which the oxygen partial pressure is controlled.

Next, the calcined product is pulverized. This crushing
It is preferable to carry out by a wet method. The pulverization of the calcined product is preferably performed until the average primary particle size of the calcined product becomes about 0.5 to 1.5 μm.

In the present invention, the additive compound may be added before calcining, but it is preferable to add the compound to the calcined material in order to obtain a higher effect. When the additive compound is added after calcining, the additive compound may be added to the calcined material and both may be pulverized and mixed, or the additional compound may be added after pulverizing the calcined material and pulverized and mixed. In any case, the pulverization and mixing are preferably performed by a wet method. In addition, it is preferable that the additive compound is pulverized until the average particle diameter becomes about 1 to 100 μm.

After calcination, it is formed into a predetermined shape, and the obtained molded body is fired. In firing, various conditions such as temperature and atmosphere may be selected to be optimal according to the main composition. For example, in the case of Ni-Zn ferrite, 1000-1350 in air or an atmosphere in which the oxygen partial pressure is controlled.
What is necessary is just to bake at about ℃ for about 1 to 10 hours.

The use of the soft magnetic ferrite produced according to the present invention is not particularly limited.
Suitable for microwave materials and the like.

[0019]

EXAMPLE An Fe ₂ O ₃ powder, a ZnO powder and a NiO powder were prepared as main component raw materials, and these were weighed so that the composition after sintering would be Ni _0.3 Zn _0.7 Fe ₂ O _4. Wet mixed for hours. The obtained mixture was calcined in air at 1150 ° C. for 5 hours, and the calcined product was wet-pulverized with a ball for 24 hours.

Then, Co was added to the pulverized material as an additive compound.
O powder, BaFe ₁₂ O ₁₉ powder or SrFe ₁₂ O ₁₉ powder was added and wet-mixed for 3 hours by a ball mill. Table 1 below shows the addition amounts of each additive compound.

Next, the mixture of the calcined product and the additive compound was subjected to wet molding to obtain a toroidal molded body.

Next, the molded body is placed in air for 115 minutes.
Bake at 0 ° C for 5 hours, outer diameter 18mm, inner diameter 12mm, height 5
A toroidal sintered compact magnetic core sample of mm was obtained.

For each sample, 50 MHz and 100 M
The initial permeability at Hz was measured. A vector impedance meter was used for the measurement. Next, each sample was subjected to a heat treatment in a magnetic field. The treatment was performed in air, the magnetic field strength was 50 kOe, the reached temperature was 600 ° C., the temperature holding time was 1 hour, and the cooling rate was 60 ° C./hour. The direction of the applied magnetic field was perpendicular to the radial direction of the toroidal sample (the axial direction of the sample). After this heat treatment in a magnetic field,
The initial magnetic permeability was measured again. Table 1 shows the measurement results.

[0024]

[Table 1]

From Table 1, the effect of the present invention is clear.
That is, in Sample No. 1 containing no additive compound, a practical initial magnetic permeability was not obtained even at 50 MHz regardless of the presence or absence of heat treatment in a magnetic field. While practical initial permeability cannot be obtained, a sufficiently high initial permeability can be obtained at 100 MHz when the sample containing the additive compound is heat-treated in a magnetic field. In addition, the sample of the present invention shown in Table 1 did not have an increased initial permeability due to the presence of a resonance frequency near 100 MHz.
The initial permeability was almost constant around 100 MHz. In particular, in the case of the sample to which CoO is added, 10 MHz to 10 MHz
It can be seen that the decrease in the initial magnetic permeability is small in the range of 0 MHz, and the effect of the heat treatment in the magnetic field is large.

For sample No. 5 shown in Table 1,
To investigate the effect of heat treatment in a magnetic field on crystal orientation,
Analysis by X-ray diffraction was performed. Note that X-rays were incident from the upper surface of the sample. An X-ray diffraction chart of Sample No. 5 is shown in FIG. The chart shown as “transverse magnetic field” in FIG. 1 is a case where the magnetic field application direction during the heat treatment in the magnetic field is the radial direction of the sample, and the chart shown as “longitudinal magnetic field” is the magnetic field during the heat treatment in the magnetic field. This is a case where the application direction is the axial direction of the sample.

FIG. 1 clearly shows that the heat treatment in a magnetic field with a vertical magnetic field increases the reflection peaks of the (111) plane and the equivalent plane. Therefore, it is understood that the (111) plane was preferentially oriented by the heat treatment in the magnetic field.

[0028]

According to the present invention, the usable limit frequency of Ni-containing ferrite is extended, and in particular, Ni-Zn ferrite can be used at 100 MHz, which has not been conventionally used.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart showing a change in crystal orientation of Ni—Zn ferrite by heat treatment in a magnetic field.

Claims (5)

[Claims] Claims: 1. A composition comprising at least nickel oxide,
A method for producing a soft magnetic ferrite, comprising a step of heat-treating a spinel-type ferrite containing at least one of o, Ba and Sr in a magnetic field. 2. The method according to claim 1, wherein the spinel ferrite is Co, B
at least one of a and Sr is CoO, B
aFe ₁₂ O ₁₉ and SrFe ₁₂ manufacturing method of a soft magnetic ferrite according to claim 1, in terms of O ₁₉ containing 0.1 to 10 wt% in total. 3. A method according to claim 1, wherein the calcined material containing at least nickel oxide contains cobalt oxide,
The method for producing a soft magnetic ferrite according to claim 1 or 2, wherein the method is produced by adding at least one of a ferrite and Sr ferrite and calcining. 4. The method for producing a soft magnetic ferrite according to claim 1, wherein the (111) plane is preferentially oriented by heat treatment in a magnetic field. 5. The method for producing a soft magnetic ferrite according to claim 1, wherein said spinel-type ferrite contains zinc oxide.