JP3492802B2 - Low loss ferrite material - Google Patents
Low loss ferrite materialInfo
- Publication number
- JP3492802B2 JP3492802B2 JP04102695A JP4102695A JP3492802B2 JP 3492802 B2 JP3492802 B2 JP 3492802B2 JP 04102695 A JP04102695 A JP 04102695A JP 4102695 A JP4102695 A JP 4102695A JP 3492802 B2 JP3492802 B2 JP 3492802B2
- Authority
- JP
- Japan
- Prior art keywords
- weight
- ferrite
- ferrite material
- less
- coo
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/34—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials non-metallic substances, e.g. ferrites
- H01F1/342—Oxides
- H01F1/344—Ferrites, e.g. having a cubic spinel structure (X2+O)(Y23+O3), e.g. magnetite Fe3O4
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- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Compounds Of Iron (AREA)
- Magnetic Ceramics (AREA)
- Soft Magnetic Materials (AREA)
Description
【0001】[0001]
【産業上の利用分野】本発明は高周波領域での損失が低
いフェライト材料に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite material having a low loss in a high frequency range.
【0002】[0002]
【従来の技術】フェライト材料はインダクター素子等と
して広く使用されている。例えば、Fe2 O3 −ZnO
−NiOを主成分とするフェライト材料(Ni−Zn系
フェライト)を用いてフェライトコアを製造し、この巻
線部にコイル線を巻回し、コイル線接続用のリードピン
をフェライトコアに取り付けた構造のインダクター素子
が使用されている。2. Description of the Related Art Ferrite materials are widely used as inductor elements and the like. For example, Fe 2 O 3 —ZnO
Of a structure in which a ferrite core containing NiO as a main component (Ni-Zn ferrite) is manufactured, a coil wire is wound around this winding portion, and a lead pin for connecting the coil wire is attached to the ferrite core. Inductor elements are used.
【0003】ところで、Ni−Zn系フェライト材料は
従来より高周波用フェライトとして多用されているが、
粒成長により結晶が大きくなると30MHz以上の高周
波領域における損失が増大してしまうことから、これを
防止するために焼成温度を低くして粒成長を抑えること
が行われている。By the way, Ni--Zn ferrite materials have been widely used as high frequency ferrites from the past.
When the crystal grows due to grain growth, the loss in the high frequency region of 30 MHz or more increases. Therefore, in order to prevent this, the firing temperature is lowered to suppress grain growth.
【0004】また、Ni−Zn系フェライト材料は高周
波領域で電気抵抗値及びQ値が高いものであるが、さら
に高いQ値を得るためにFe2 O3 を数%過剰に加えた
フェライトにCoOを添加し、焼成後に再度焼鈍するこ
とも行われている。Ni-Zn type ferrite materials have high electric resistance and Q value in a high frequency region, but in order to obtain a higher Q value, ferrite containing Fe 2 O 3 in a few percent excess is added to CoO. Is added, and annealing is performed again after firing.
【0005】[0005]
【発明が解決しようとする課題】ところが、従来のNi
−Zn系フェライトにおいて、結晶径を制御するために
焼成温度を低くした場合、焼結密度が5.0g/cm3
以下と理論密度に比べて著しく低くなるため、機械的強
度が低下して信頼性が悪くなるだけでなく、焼成時の収
縮率の制御が難しくなって寸法精度が悪くなり、製造歩
留りが低下するという問題点があった。However, the conventional Ni
In the Zn-based ferrite, the sintering density is 5.0 g / cm 3 when the firing temperature is lowered to control the crystal diameter.
Since it is significantly lower than the theoretical density below, not only the mechanical strength is lowered and the reliability is deteriorated, but also it is difficult to control the shrinkage ratio during firing, the dimensional accuracy is deteriorated, and the manufacturing yield is decreased. There was a problem.
【0006】また、Q値を高めるために、Fe2 O3 を
数%過剰に加えたNi−Zn系フェライトにCoOを添
加した場合、焼成後に焼鈍する必要があるため、製造工
程が煩雑になるという問題点があった。When CoO is added to Ni--Zn type ferrite containing Fe 2 O 3 added in excess of several% in order to increase the Q value, it is necessary to anneal after firing, which complicates the manufacturing process. There was a problem.
【0007】この他に、Ni−Zn系フェライトに各種
添加物を加えることによって特性を高めることも提案さ
れているが(特開昭49−2092号、49−2093
号、特公昭52−27358号公報等参照)、いずれも
上記問題点を解決するものではなかった。In addition to the above, it has been proposed to add various additives to Ni-Zn type ferrite to improve the characteristics (Japanese Patent Laid-Open Nos. 49-2092 and 49-2093).
Japanese Patent Publication No. 52-27358, etc.) did not solve the above problems.
【0008】そこで本発明は、30MHz以上で使用さ
れる高周波用途のNi−Zn系フェライト材料におい
て、焼結密度が5.0g/cm3 以上で、焼成後の焼鈍
を必要とせず、Q値が高く、損失が小さいフェライト材
料を得ることを目的とする。In view of the above, the present invention provides a Ni-Zn type ferrite material used at a frequency of 30 MHz or higher for high frequency use, has a sintered density of 5.0 g / cm 3 or more, does not require annealing after firing, and has a Q value. The purpose is to obtain a ferrite material that is high and has low loss.
【0009】[0009]
【課題を解決するための手段】本発明は、55〜75重
量%のFe2 O3 と、1〜25重量%のZnOと、5〜
35重量%のNiOと、0.1〜5重量%のCuOとを
主成分とするフェライト材料において、上記主成分10
0重量%に対し、0.01〜2重量%のCoOと、0.
01〜1重量%のBi2 O3 と、0.01〜2重量%の
Al2 O3 を含有することを特徴とする。According to the present invention, 55 to 75% by weight of Fe 2 O 3 and 1 to 25% by weight of ZnO are included.
In a ferrite material containing 35% by weight of NiO and 0.1 to 5% by weight of CuO as main components, the main component 10
0.01 to 2% by weight of CoO with respect to 0% by weight;
It is characterized by containing 01 to 1% by weight of Bi 2 O 3 and 0.01 to 2 % by weight of Al 2 O 3 .
【0010】即ち、本発明は、Ni−Zn−Cu系フェ
ライトに対して、所定量のCoOとBi2 O3 とAl2
O3 を添加することによって、焼結密度が5.0g/c
m3以上で、焼成後の焼鈍を必要とせず、30MHz以
上の高周波領域での損失特性を向上できるようにしたも
のである。That is, according to the present invention, a predetermined amount of CoO, Bi 2 O 3 and Al 2 is added to Ni-Zn-Cu type ferrite.
With the addition of O 3 , the sintered density is 5.0 g / c
With m 3 or more, it is possible to improve the loss characteristics in a high frequency region of 30 MHz or more without requiring annealing after firing.
【0011】また、上記添加成分の範囲を限定したの
は、CoO又はBi2 O3 又はAl2O3 0.01重量
%未満では30MHz以上の高周波領域でのQ値が低下
してしまい、一方CoOが2重量%を超えると温度特性
が劣化し、またBi2 O3 が1重量%を超えると粒成長
が起こってQ値が著しく低下し、さらにAl2 O3 が2
重量%を超えると焼結性が低下してしまうためである。Further, the range of the above-mentioned additive components is limited in that if the content of CoO or Bi 2 O 3 or Al 2 O 3 is less than 0.01% by weight, the Q value in the high frequency region of 30 MHz or more decreases. CoO is deteriorated temperature characteristic exceeds 2 wt%, and Bi 2 O 3 is decreased significantly Q value occurred exceeds the grain growth of 1% by weight, and more Al 2 O 3 2
This is because the sinterability deteriorates when the content exceeds the weight percentage.
【0012】さらに、Ni−Zn−Cu系フェライトの
主成分の組成比を上記範囲としたのは、Fe2 O3 が5
5重量%未満では透磁率が低下し、Fe2 O3 が75重
量%を超えるとQ値が低下し、ZnOが25重量%を超
えるとキュリー点が低下し、NiOが35重量%を超え
ると加圧安定性が悪くなり、CuOが5重量%を超える
と磁気特性が劣化するためである。Further, the composition ratio of the main component of the Ni-Zn-Cu type ferrite is set within the above range because Fe 2 O 3 is 5
If it is less than 5% by weight, the magnetic permeability is lowered, if Fe 2 O 3 exceeds 75% by weight, the Q value is lowered, and if ZnO exceeds 25% by weight, the Curie point is lowered, and if NiO exceeds 35% by weight. This is because the pressurization stability deteriorates, and when CuO exceeds 5% by weight, the magnetic characteristics deteriorate.
【0013】また、本発明のフェライト材料は、上記成
分以外に3重量%以下のSiO2 及び/又は2重量%以
下のMgOを含んでいても良い。このSiO2 とMgO
は結晶粒界の抵抗値を高めることができるため、高周波
でのQ値を高くすることができるが、SiO2 が3重量
%を超えると焼結性と透磁率が低下し、MgOが2重量
%を超えると温度特性が劣化するため、上記範囲内が好
ましい。Further, the ferrite material of the present invention may contain, in addition to the above components, 3% by weight or less of SiO 2 and / or 2% by weight or less of MgO. This SiO 2 and MgO
Can increase the resistance of the crystal grain boundaries, so that the Q value at high frequencies can be increased. However, when SiO 2 exceeds 3% by weight, the sinterability and magnetic permeability decrease, and MgO is 2% by weight. %, The temperature characteristics deteriorate, so the above range is preferred.
【0014】本発明のフェライト材料の製造方法は、上
記範囲となるように各原料を調合し、ボールミル等で粉
砕混合した後、スプレードライヤー等で造粒し、得られ
た粉体をプレス成形にて所定形状に成形し、1000〜
1300℃の範囲で焼成することによって得られる。In the method for producing a ferrite material of the present invention, the respective raw materials are mixed so as to fall within the above range, pulverized and mixed by a ball mill or the like, and then granulated by a spray dryer or the like, and the obtained powder is press-molded. To a predetermined shape,
It is obtained by firing in the range of 1300 ° C.
【0015】[0015]
【実施例】実施例1
64重量%のFe2 O3 と、31重量%のNiOと、
1.5重量%のZnOを、3.5重量%のCuOからな
るフェライト粉末100重量%に対し、2重量%のSi
O2 と1重量%のMgOを添加し、さらにCoO、Bi
2 O3 、Al2 O3 の添加量を表1に示すように種々に
変化させて各原料を調合した。 Example 1 64% by weight of Fe 2 O 3 and 31% by weight of NiO,
1.5 wt% ZnO was added to 2 wt% Si based on 100 wt% ferrite powder consisting of 3.5 wt% CuO.
O 2 and 1 wt% MgO were added, and further CoO, Bi
Each raw material was prepared by variously changing the addition amounts of 2 O 3 and Al 2 O 3 as shown in Table 1.
【0016】得られた原料を振動ミルで混合した後、8
00〜900℃で仮焼し、この仮焼粉体をボールミルに
て粉砕し、所定のバインダを加えて造粒した後、圧縮成
形してトロイダルコイル状に成形した。この成形体を1
100℃で2時間焼成したのち、得られた焼結体に線径
0.2μmの導線を巻付け、YHP社製LCRメータで
周波数30MHzにて透磁率μとQ値を測定した。損失
係数は、tanδ/μ(=1/μQ)で計算して求め
た。また、得られた焼結体の密度も測定した。After mixing the obtained raw materials with a vibration mill, 8
The powder was calcined at 00 to 900 ° C., and the calcined powder was crushed by a ball mill, added with a predetermined binder, granulated, and then compression molded to form a toroidal coil. This molded body 1
After firing at 100 ° C. for 2 hours, a conductor wire having a wire diameter of 0.2 μm was wound around the obtained sintered body, and the magnetic permeability μ and the Q value were measured at a frequency of 30 MHz with an LCR meter manufactured by YHP. The loss coefficient was calculated by tan δ / μ (= 1 / μQ). Further, the density of the obtained sintered body was also measured.
【0017】結果は表1に示す通りであり、CoO,B
i2 O3 ,Al2 O3 の添加量が本発明の範囲外である
No.1〜7、13ではtanδ/μが500×10-6
以上と損失係数が大きく、さらにNo.2〜7では焼結
密度が5.0g/cm3 未満と小さかった。The results are shown in Table 1, and CoO, B
amount of i 2 O 3, Al 2 O 3 is out of the scope of the present invention No. In 1 to 7 and 13, tan δ / μ is 500 × 10 -6
The loss coefficient is large as above, and further, No. In Nos. 2 to 7, the sintered density was as small as less than 5.0 g / cm 3 .
【0018】これらに対し、本発明実施例であるNo.
8〜12ではtanδ/μが500×10-6以下と損失
係数が小さく、かつ焼結密度が5.0g/cm3 以上と
大きかった。On the other hand, in No. 1 which is the embodiment of the present invention.
In Nos. 8 to 12, tan δ / μ was as small as 500 × 10 −6 or less and the loss factor was small, and the sintered density was as large as 5.0 g / cm 3 or more.
【0019】[0019]
【表1】 [Table 1]
【0020】実施例2
次に、65重量%のFe2 O3 と、22重量%のNiO
と、9重量%のZnOと、4重量%のCuOからなるフ
ェライト粉末100重量%に対し、2.5重量%のSi
O2 と1重量%のMgOを添加し、さらにCoO,Bi
2 O3 ,Al2O3 の添加量を表2に示すように種々に
変化させて各原料を調合した。それぞれ上記実施例と同
様にしてフェライトコアを作製し、周波数30MHzで
の透磁率μとQ値を測定してtanδ/μを求め、焼結
密度を測定した。 Example 2 Next, 65% by weight of Fe 2 O 3 and 22% by weight of NiO were used.
And 100 wt% of ferrite powder consisting of 9 wt% ZnO and 4 wt% CuO, 2.5 wt% Si
O 2 and 1 wt% MgO were added, and further CoO, Bi
Each raw material was prepared by variously changing the addition amounts of 2 O 3 and Al 2 O 3 as shown in Table 2. Ferrite cores were produced in the same manner as in the above-mentioned examples, and the magnetic permeability μ and Q value at a frequency of 30 MHz were measured to obtain tan δ / μ, and the sintered density was measured.
【0021】結果は表2に示す通りであり、CoO,B
i2 O3 ,Al2 O3 の添加量が本発明の範囲外である
No.14〜17、22、23では、tanδ/μが5
00×10-6以上と損失係数が大きく、さらにNo.1
4、15では焼結密度が5.0g/cm3 未満と小さか
った。The results are shown in Table 2. CoO, B
amount of i 2 O 3, Al 2 O 3 is out of the scope of the present invention No. In 14 to 17, 22, and 23, tan δ / μ is 5
The loss factor is as large as 00 × 10 −6 or more. 1
In Nos. 4 and 15, the sintered density was as small as less than 5.0 g / cm 3 .
【0022】これらに対し、本発明実施例であるNo.
18〜21ではtanδ/μが300×10-6以下と損
失係数が小さく、かつ焼結密度が5.0g/cm3 以上
と大きかった。On the other hand, in No. 1 which is the embodiment of the present invention.
In Nos. 18 to 21, the tan δ / μ was 300 × 10 −6 or less, which was a small loss factor, and the sintered density was 5.0 g / cm 3 or more, which was large.
【0023】[0023]
【表2】 [Table 2]
【0024】実施例3
次に、60.5重量%のFe2 O3 と、22.5重量%
のNiOと、13重量%のZnOと、4重量%のCuO
からなるフェライト粉末100重量%に対し、2.5重
量%のSiO2 を添加し、さらにCoO,Bi2 O3 ,
Al2 O3 の添加量を表3に示すように種々に変化させ
て各原料を調合した。それぞれ上記実施例と同様にして
フェライトコアを作製し、周波数30MHzでの透磁率
μとQ値を測定してtanδ/μを求め、焼結密度を測
定した。 Example 3 Next, 60.5 wt% Fe 2 O 3 and 22.5 wt%
NiO, 13 wt% ZnO, 4 wt% CuO
2.5% by weight of SiO 2 was added to 100% by weight of ferrite powder consisting of CoO, Bi 2 O 3 ,
Each raw material was prepared by variously changing the addition amount of Al 2 O 3 as shown in Table 3. Ferrite cores were produced in the same manner as in the above-mentioned examples, and the magnetic permeability μ and Q value at a frequency of 30 MHz were measured to obtain tan δ / μ, and the sintered density was measured.
【0025】結果は表3に示す通りであり、CoO,B
i2 O3 ,Al2 O3 の添加量が本発明の範囲外である
No.24〜27、32では、tanδ/μが500×
10-6以上と損失係数が大きく、さらにNo.26では
焼結密度が5.0g/cm3未満と小さかった。The results are shown in Table 3, and CoO, B
amount of i 2 O 3, Al 2 O 3 is out of the scope of the present invention No. In 24-27 and 32, tan δ / μ is 500 ×
The loss factor is as large as 10 -6 or more, and further, No. In No. 26, the sintered density was as small as less than 5.0 g / cm 3 .
【0026】これらに対し、本発明実施例であるNo.
28〜31ではtanδ/μが500×10-6以下と損
失係数が小さく、焼結密度が5.0g/cm3 以上と大
きかった。On the other hand, in No. 1 which is an embodiment of the present invention.
In Nos. 28 to 31, tan δ / μ was 500 × 10 −6 or less and the loss factor was small, and the sintered density was 5.0 g / cm 3 or more.
【0027】[0027]
【表3】 [Table 3]
【0028】さらに実験を重ねた結果、主成分の組成比
として、Fe2 O3 が55〜75重量%、ZnOが1〜
25重量%、NiOが5〜35重量%、CuOが0.1
〜5重量%の範囲を満たすフェライト材料に、0.01
〜2重量%のCoOと、0.01〜1重量%のBi2 O
3 と、0.01〜2重量%のAl2 O3 を添加すること
により、30MHz以上の高周波領域でtanδ/μが
500×10-6以下と低損失で、かつ焼結密度が5.0
g/cm3 以上の緻密なフェライトコアを得られること
がわかった。As a result of further experiments, as a composition ratio of the main components, Fe 2 O 3 is 55 to 75% by weight, and ZnO is 1 to 1.
25% by weight, NiO 5 to 35% by weight, CuO 0.1
To the ferrite material satisfying the range of
To 2% by weight of CoO, 0.01 to 1 wt% of Bi 2 O
By adding 3 and 0.01 to 2 % by weight of Al 2 O 3 , the tan δ / μ is 500 × 10 −6 or less in the high frequency region of 30 MHz or more, and the sintering density is 5.0 or less.
It was found that a dense ferrite core having a g / cm 3 or more can be obtained.
【0029】なお、以上の実施例ではフェライトコアに
ついてのみ述べたが、本発明のフェライト材料はその他
のさまざまな用途に用いることができる。例えば、各種
電子部品を搭載したり、分割して電子部品とするための
フェライト基板や、電磁波を吸収して磁気ヘッド等をシ
ールドしたり、発熱するための電磁波吸収体等として用
いることができる。Although only the ferrite core has been described in the above embodiments, the ferrite material of the present invention can be used for various other purposes. For example, it can be used as a ferrite substrate for mounting various electronic parts or for dividing into electronic parts, for shielding a magnetic head or the like by absorbing electromagnetic waves, or as an electromagnetic wave absorber for generating heat.
【0030】[0030]
【発明の効果】以上のように 本発明によれば、55〜
75重量%のFe2 O3 と、1〜25重量%のZnO
と、5〜35重量%のNiOと、0.1〜5重量%のC
uOを主成分とするフェライト材料において、上記主成
分100重量%に対し、0.01〜2重量%のCoO
と、0.01〜1重量%のBi2 O3 と、0.01〜2
重量%のAl2 O3 を含有させることによって、焼成後
に再度焼鈍する必要がなく、高密度で機械的強度や寸法
精度が高く、高周波領域での損失が低いフェライト材料
を提供することができる。As described above, according to the present invention,
75 wt% Fe 2 O 3 and 1-25 wt% ZnO
And 5 to 35 wt% NiO and 0.1 to 5 wt% C
In a ferrite material containing uO as a main component, 0.01 to 2 wt% of CoO is used with respect to 100 wt% of the main component.
And 0.01 to 1% by weight of Bi 2 O 3 and 0.01 to 2
By including Al 2 O 3 by weight%, it is possible to provide a ferrite material that does not need to be annealed again after firing, has high density, high mechanical strength and dimensional accuracy, and low loss in a high frequency region.
Claims (2)
5重量%のZnOと、5〜35重量%のNiOと、0.
1〜5重量%のCuOから成る主成分100重量%に対
し、0.01〜2重量%のCoOと、0.01〜1重量
%のBi2 O3 と、0.01〜2重量%のAl2 O3 を
含有し、周波数30MHzにおける損失係数(tanδ
/μ)が500×10 −6 以下であることを特徴とする
低損失フェライト材料。1. Fe 2 O 3 in an amount of 55 to 75% by weight, and 1 to 2
5 wt% ZnO, 5-35 wt% NiO, and
With respect to 100% by weight of the main component composed of 1 to 5% by weight CuO, 0.01 to 2 % by weight of CoO, 0.01 to 1% by weight of Bi 2 O 3, and 0.01 to 2 % by weight of It contains Al 2 O 3 and has a loss factor (tan δ at a frequency of 30 MHz.
/ Mu) is low-loss ferrite material, characterized in der Rukoto 500 × 10 -6 or less.
2重量%以下のMgOを含有することを特徴とする請求
項1記載の低損失フェライト材料。2. The low-loss ferrite material according to claim 1, further containing 3 wt% or less of SiO 2 and / or 2 wt% or less of MgO.
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JP04102695A JP3492802B2 (en) | 1995-02-28 | 1995-02-28 | Low loss ferrite material |
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JP04102695A JP3492802B2 (en) | 1995-02-28 | 1995-02-28 | Low loss ferrite material |
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JP3492802B2 true JP3492802B2 (en) | 2004-02-03 |
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Families Citing this family (11)
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KR100210369B1 (en) * | 1997-02-12 | 1999-07-15 | 홍성용 | A composition for absorbing electromagnetic wave and a method for manufacturing the same |
JP3672161B2 (en) * | 1997-07-16 | 2005-07-13 | Tdk株式会社 | Ferrite manufacturing method and inductor manufacturing method |
KR100320944B1 (en) * | 1997-12-11 | 2002-03-08 | 이형도 | Magnetic material for use in high frequency inductor |
JPH11243024A (en) * | 1998-02-25 | 1999-09-07 | Kyocera Corp | Electrical equipment applicable to non-contact charger |
US6191934B1 (en) * | 1998-10-02 | 2001-02-20 | Sarnoff Corporation & Co., Ltd. | High dielectric constant embedded capacitors |
JP5137275B2 (en) * | 1999-11-26 | 2013-02-06 | 京セラ株式会社 | High saturation magnetic flux density ferrite material and ferrite core using the same |
JP4557690B2 (en) * | 2004-11-25 | 2010-10-06 | 京セラ株式会社 | Coil built-in board |
KR20160118973A (en) | 2015-04-02 | 2016-10-12 | 티디케이가부시기가이샤 | Ferrite composition and electronic component |
JP6024843B1 (en) * | 2015-04-02 | 2016-11-16 | Tdk株式会社 | Ferrite composition and electronic component |
JP6740817B2 (en) | 2016-08-30 | 2020-08-19 | Tdk株式会社 | Ferrite composition, ferrite sintered body, electronic component and chip coil |
CN106495677A (en) * | 2016-10-10 | 2017-03-15 | 电子科技大学 | A kind of high-strength thermal-shock power nickel-zinc ferrite and preparation method thereof |
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1995
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