JP2006213531A - Manganese-cobalt-zinc-based ferrite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Mn-Co-Zn-based ferrite in which the standardized impedance in a high frequency region is drastically improved while the standardized impedance in a low frequency region is kept. <P>SOLUTION: The Mn-Co-Zn-based ferrite comprises 45.0 to <50.0 mol% Fe<SB>2</SB>O<SB>3</SB>, 0.5-4.0 mol% CoO, 15.5-24.0 mol% ZnO and the balance being MnO as basic components and contains 0.001-0.05 mass% in total of one or two kinds of SrO and BaO as additive components. The content of P, B, S and Cl contained in the ferrite is respectively <50 mass ppm P, <20 mass ppm B, <30 mass ppm S and <50 mass ppm Cl. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an Mn-Co-Zn ferrite exhibiting good frequency characteristics, having a normalized impedance of 2.5 Ω / mm or more at 100 kHz and 60 Ω / mm or more at 20 MHz.
Here, the above-mentioned standardized impedance means that the measured impedance value is proportional to the square of the number of turns of the winding, and the value changes depending on the shape. Is standardized for comparison, and is defined by the following equation.
Z = (R · l) / (A · N ² )
Where Z: normalized impedance, R: impedance measurement value (Ω), l: core magnetic path length (mm), A: core cross-sectional area (mm ² ), N: number of core winding turns

  Typical examples of the soft magnetic oxide magnetic material include Mn-Zn ferrite. This Mn-Zn ferrite has low loss, high saturation magnetic flux density, high initial permeability, and high impedance compared to other oxide magnetic materials. Utilizing these characteristics For example, a low-loss, high-saturation magnetic flux density material is mainly used for a power transformer core and the like, and a high impedance material is mainly used for a noise filter core and the like.

However, the conventional Mn-Zn ferrite contains about 2 mass% or more of Fe ^{2+ in the} basic component, and since this Fe ²⁺ causes electrons to be exchanged with Fe ³⁺ , the specific resistance is very small. There is a disadvantage that it stops at the value (0.1Ωm). Therefore, when the frequency region to be used becomes high, the loss due to the eddy current flowing in the ferrite increases rapidly. For example, when focusing on the normalized impedance, the frequency increases in the low frequency region in the kHz region, but rises as the frequency increases, but is affected by the eddy current loss and reaches a peak at several MHz at the highest, and the higher frequency region. Then, the normalized impedance continues to decrease. As a result, it cannot cope with a frequency of 10 MHz or more.

Therefore, Ni-Zn ferrite is mainly used as the ferrite used in this frequency region. The reason for this is that Ni-Zn ferrite has a very high specific resistance of 10 ⁵ Ωm or more, approximately 10,000 times that of Mn-Zn ferrite, and is less affected by eddy current loss. This is because the band can have a higher normalized impedance than the Mn-Zn ferrite. However, the Ni-Zn ferrite has a problem that the normalized impedance in the low frequency region of the khz region is lower than that of the Mn-Zn ferrite.

Therefore, attempts have been made to develop materials that maintain high standardized impedance up to a higher frequency region by increasing the specific resistance of Mn-Zn ferrite and suppressing eddy current loss. As an example, Patent Document 1 and Patent Document 2 disclose Mn-Zn-based ferrites in which the Fe ₂ O ₃ component in the raw material is less than 50 mol%, the Fe ²⁺ content is reduced, and the specific resistance is increased. Yes. Patent Documents 3 and 4 disclose techniques for improving magnetic properties by adding CoO having positive magnetic anisotropy to the Mn-Zn ferrite.
Japanese Patent Laid-Open No. 7-230909 JP 2000-277316 A Japanese Patent Laid-Open No. 2001-220221 JP 2003-059712 A

However, the Mn-Zn ferrite described in the above Patent Documents 1 to 4 with Fe ₂ O ₃ component less than 50 mol% often causes deterioration of magnetic properties when actually produced. It has been difficult to stably obtain Mn-Zn ferrite having high standardized impedance even in a high frequency region. Furthermore, since the Mn—Co—Zn ferrite disclosed in Patent Document 3 and Patent Document 4 is fired in a very low oxygen concentration atmosphere, strict atmosphere control of the firing furnace is required. The Therefore, industrial nitrogen gas containing at least 1 to 20 volppm of oxygen cannot be used, and it is necessary to use pure nitrogen. There are problems in both production efficiency and cost for industrialization.

  An object of the present invention is to provide an Mn-Co-Zn ferrite in which the above-mentioned problems of Mn-Zn ferrite and Mn-Co-Zn ferrite are solved and the frequency characteristics of normalized impedance are improved. .

The inventors have repeatedly studied paying attention to the additive component in order to improve the frequency characteristics of the normalized impedance. As a result, an appropriate amount of one or two of SrO and BaO was added as an additional component to the Mn-Co-Zn ferrite with Fe ₂ O ₃ content of less than 50 mol% and Fe ²⁺ content reduced. By doing so, it was found that the standardized impedance in the high frequency region of 20 MHz can be significantly improved without lowering the standardized impedance in the low frequency region of 100 kHz.

  Furthermore, the inventors examined the reason why excellent magnetic properties could not be stably obtained in the Mn-Co-Zn ferrite, and found that abnormal grain growth was involved in the ferrite manufacturing process. . Abnormal grain growth is a phenomenon that occurs when the balance of grain growth is disrupted locally for some reason, and is particularly often observed during production using powder metallurgy. In this abnormally grown grain, substances that greatly impede the movement of the domain wall such as impurities and lattice defects are mixed, and at the same time, the generation of crystal grain boundaries becomes insufficient. Is significantly degraded.

Therefore, paying attention to the fact that most of the raw material of ferrite, especially the main raw material Fe ₂ O ₃ is produced from the scale generated in the iron making process, the scale-derived Fe ₂ O ₃ raw material and the above abnormal grain growth And investigated the relationship. As a result, ferrite containing a large amount of impurities such as P, B, S and Cl inevitably mixed in steel (scale) is likely to induce abnormal grain growth, that is, in the Fe ₂ O ₃ raw material. It has been newly found that the contained impurities P, B, S and Cl have a serious adverse effect on various properties such as magnetic properties and specific resistance of the soft magnetic ferrite.

That is, in the technologies of Patent Document 1, Patent Document 3, and Patent Document 4, since there is no restriction on the amount of the impurities, it is described in the documents only by following the technical contents disclosed in these documents. It is actually difficult to manufacture Mn-Zn ferrites with desirable characteristics, and even better than those described in this document, which has a standardized impedance of 60 Ω / mm or more at 20 MHz. It was impossible to get. In the technique of Patent Document 2, P is limited, but other impurities are not considered.
The present invention has been developed based on the above findings.

That is, the present invention comprises Fe ₂ O ₃ : 45.0 to less than 50.0 mol%, CoO: 0.5 to 4.0 mol%, ZnO: 15.5 to 24.0 mol%, and the balance MnO. In the Mn-Co-Zn ferrite containing 0.001 to 0.050 mass% in total of any one or two, the amount of P, B, S and Cl contained in this ferrite is P: less than 50 massppm, B: The Mn-Co-Zn ferrite is characterized by being less than 20 massppm, S: less than 30 massppm, and Cl: less than 50 massppm.

The Mn—Co—Zn-based ferrite of the present invention further includes any one or two of CaO: 0.005 to 0.200 mass% and SiO ₂ : 0.001 to 0.050 mass% as the additive component. .

Further, Mn-Co-Zn ferrite of the present invention, further as the additive _{component, ZrO 2: 0.005~0.100mass%, Ta} 2 O 5: 0.005~0.100mass%, HfO 2: 0.005~0.100mass% and Nb ₂ O ₅ : One or more of 0.005 to 0.100 mass% are contained.

  According to the present invention, the standardized impedance in the high frequency region is greatly improved while the Curie temperature is 100 ° C. or higher and the high standardized impedance in the low frequency region is maintained. Specifically, the Curie temperature is 2.5 at 100 kHz. It is possible to provide an Mn—Co—Zn-based ferrite having excellent characteristics of Ω / mm or more and 60 Ω / mm or more at 20 MHz. The ferrite of the present invention can effectively suppress the occurrence of abnormal grain growth and characteristic deterioration due to the change in atmosphere by limiting the amount of impurities. It also has an effect that it can be used, or industrial nitrogen gas containing a large amount of oxygen can be used during cooling during firing.

In the present invention, the reason why the basic component is limited to the above range will be described.
The basic component composition described below, all of the Fe and Mn is obtained by converting as Fe ₂ O ₃ and MnO contained.
_{Fe 2 O 3: Fe 2 O} 3 less than 45.0～50.0Mol%, which is a basic component, if included in excess, as described above, the resistivity Fe ²⁺ content is increased is reduced, at 20MHz The standardized impedance is significantly reduced. In order to avoid this, Fe ₂ O ₃ contained in the ferrite needs to be suppressed to less than 50 mol%. However, if the amount is too small, the Curie temperature is lowered and the normalized impedance is lowered at 100 kHz. Therefore, it is necessary to contain at least 45.0 mol%.

CoO: 0.1-4.0mol%
CoO has the effect of improving the normalized impedance at 100 kHz and 20 MHz by adding an appropriate amount, and is contained in an amount of 0.1 mol% or more. However, if the amount is too large, the standardized impedance is lowered, so the content is limited to 4.0 mol% or less.

ZnO: 15.5-14.0 mol%
Since ZnO has the effect of improving the normalized impedance at 100 kHz, it is necessary to contain 15.5 mol% or more. However, if the content is too high, the Curie temperature will be lowered, and the magnetism will be lost below the heat insulation heat resistance temperature of the Y class electric wire defined in JIS C 4003. Cause a practical problem. Therefore, the upper limit is made 24.0 mol% or less.

MnO: Remainder The ferrite of the present invention is an Mn-Co-Zn ferrite, and the basic component is MnO with the remainder other than the above-mentioned Fe ₂ O ₃ , CoO, and ZnO. The reason for using MnO is to realize good magnetic characteristics such that the normalized impedance at 100 kHz is 2.5 Ω / mm or more.

SrO, BaO: 0.001 to 0.050 mass% in total of 1 type or 2 types
SrO and BaO are both high melting point oxides, and segregate at the ferrite grain boundaries to increase the specific resistance, thereby suppressing eddy current loss and improving the normalized impedance at 20 MHz. . SrO and BaO also have the effect of suppressing abnormal grain growth. Therefore, it is necessary to contain one or two of SrO and BaO in a total amount of 0.001 mass% or more. However, when excessively added, abnormal grain growth is induced and the normalized impedance is lowered, so the upper limit is made 0.050 mass%.

P: less than 50 massppm, B: less than 20 massppm, S: less than 30 massppm, and Cl: less than 50 massppm P, B, S, and Cl are impurity components inevitably contained in the raw iron oxide. These impurity components have no problem as long as their content is extremely small, but when they are contained in a predetermined amount or more, abnormal grain growth of ferrite is induced and seriously adversely affects various properties of ferrite. In the ferrite having an Fe ₂ O ₃ content of less than 50 mol% according to the present invention, crystal grain growth tends to proceed and abnormal grain growth tends to occur more easily than a ferrite having the same content of 50 mol% or more. In order to suppress this abnormal grain growth, it is necessary to limit the contents of P, B, S and Cl to less than 50, 20, 30 and 50 massppm, respectively. In order to suppress the contents of P, B, S, and Cl within the above range, it is preferable to use a high-purity raw material with a small impurity content for Fe ₂ O ₃ , MnO, ZnO or the like used as the raw material. Further, the medium used for mixing and pulverizing such as a ball mill may be mixed due to wear, and therefore, it is desirable to use a medium having few impurities.

In addition to the basic component, additive component, and impurity component, the following additive component can be added to the Mn—Co—Zn ferrite of the present invention.
_{CaO: 0.005~0.200mass%, SiO 2:} 1 kind of 0.001～0.050Mass% or two
Both CaO and SiO ₂ have the function of increasing the electrical resistance of ferrite by segregating at the grain boundaries, suppressing eddy current loss, and increasing the normalized impedance at 20 MHz. However, to obtain this effect, it is necessary to add 0.005 mass% or more and / or SiO ₂ more than 0.001% of CaO. On the other hand, when too much is added, abnormal grain growth in the ferrite grains is induced, and both normalized impedances at 100 kHz and 20 MHz are lowered. Therefore, the upper limit is CaO: 0.200mass%, SiO _2: to 0.050 mass%.

One or more selected from ZrO ₂ : 0.005 to 0.100 mass%, Ta ₂ O ₅ : 0.005 to 0.100 mass%, HfO ₂ : 0.005 to 0.100 mass% and Nb ₂ O ₅ : 0.005 to 0.100 mass%
ZrO ₂ , Ta ₂ O ₅ , HfO _2, and Nb ₂ O ₅ are all compounds having a high melting point, and when added to Mn-Co-Zn ferrite, the crystal grains are reduced to reduce the specific resistance. It has the function of increasing the standardized impedance at 20 MHz. However, when the addition amount is less than the above appropriate range, the effect cannot be obtained. On the other hand, when the addition amount is large, both normalized impedances of 100 kHz and 20 MHz are lowered due to generation of abnormal grains. For this reason, it is desirable that each be within the above range.

  In addition, although the additive component demonstrated above can also acquire the effect, even if it adds each independently, even when combining and adding them, the same effect is exhibited. Even in this case, in order to suppress the occurrence of abnormal grain growth and the decrease in normalized impedance, it is desirable to suppress the amount of addition in the above range.

Next, a preferred method for producing the Mn—Co—Zn ferrite of the present invention will be described.
First, raw material powders of Fe ₂ O ₃ , ZnO, CoO and MnO are weighed so as to have a predetermined ratio, and these are mixed thoroughly and calcined, and this calcined powder is mixed with one kind of SrO and BaO. Or, two kinds are added in a total weight of 0.001 to 0.050 mass% and pulverized together with the calcined powder. When other additive components are added, they are also added and pulverized. In this operation, it is necessary to sufficiently homogenize so that the concentration of the added component is not biased. The powder of the target composition obtained by pulverization is granulated using an organic binder such as polyvinyl alcohol, formed by applying pressure, and then fired to obtain a ferrite sintered body.

  In addition, since the Mn-Co-Zn ferrite of the present invention limits the amount of impurities, it is a problem when using a powder metallurgical technique, and it is also problematic for abnormal grain growth and changes in atmosphere during firing. Less likely to cause degradation of normalized impedance. Therefore, as described above, a powder metallurgy technique can be used during production, and industrial nitrogen containing 1 to 20 volppm of oxygen can be used during cooling after firing.

The Mn-Co-Zn ferrite thus obtained has significantly improved high-frequency characteristics of standardized impedance compared to the conventional Mn-Zn ferrite containing 50 mol% or more of Fe ₂ O ₃ as a basic component. Further, by containing an appropriate amount of one or two of SrO and BaO, the normalized impedance at 20 MHz can be greatly improved as compared with the case where they are not added.

Using a ball mill, each raw material powder weighed so that Fe ₂ O ₃ , ZnO, CoO and MnO have the ratios shown in Table 1 when all the contained Fe and Mn are converted as Fe ₂ O ₃ and MnO. After mixing for 16 hours, calcination was performed in air at 925 ° C. for 3 hours. Next, SrO and BaO are weighed and added to the calcined powder in the ratios shown in Table 1 and pulverized with a ball mill for 12 hours. The obtained pulverized powder is granulated by adding polyvinyl alcohol. The toroidal core was molded by applying a pressure of 118 MPa. After that, the compact was placed in a firing furnace and fired at a maximum temperature of 1350 ° C. Cooling after firing was carried out in a temperature range from 1100 ° C to 500 ° C, and an industrial nitrogen stream with an oxygen partial pressure of 10 volppm. A sintered core having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm was obtained. For each sample obtained in this way, the Curie temperature was measured, and the normalized impedance was calculated from the impedance at 100 kHz and 20 MHz measured by applying a 10-turn winding. In addition, since the raw materials including iron oxide were all high-purity materials, the final contents of P, B, S, and Cl were less than 5 massppm in all samples.

The measurement results of Curie temperature and normalized impedance are shown together in Table 1. From Table 1, Sample Nos. 1-3, 1-5, 1-6, 1-13, and 1-14, which are examples of the invention, have a Curie temperature of 100 ° C. or higher, a normalized impedance of 100 kHz, 2.5 Ω / mm or higher, and It has excellent characteristics of 60Ω / mm or more at 20MHz. On the other hand, in the sample numbers 1-1 and 1-2 of the comparative example in which Fe ₂ O ₃ is 50.0 mol% or more, the normalized impedance at 20 MHz is greatly lowered. On the other hand, Sample Nos. 1-15 of the comparative example lacking Fe ₂ O ₃ show a decrease in Curie temperature and a decrease in normalized impedance at 100 kHz. Moreover, in the sample numbers 1-4 of the comparative example which does not contain CoO, the value of the normalized impedance of 100 kHz is lowered. On the contrary, in the sample numbers 1-10 of the comparative example containing a large amount, both the normalized impedance values at 100 kHz and 20 MHz are lowered. In addition, in Sample No. 1-11 of the comparative example containing ZnO in a larger amount than the claimed range, the Curie temperature is less than 100 ° C. On the contrary, in the sample numbers 1-12 of the comparative example in which ZnO is insufficient, the normalized impedance at 100 kHz is lowered. Paying attention to the additive components SrO and BaO, in the invention example containing these in a range of 0.001 to 0.050 mass% in total of one or two, both have high normalized impedance at 100 kHz and 20 MHz. However, in Comparative Sample Nos. 1-7 that do not include these, the normalized impedance at 20 MHz remains low. Moreover, in the sample numbers 1-8 and 1-9 of the comparative examples including these in total of 0.050 mass% or more, the normalized impedance at 100 kHz is reduced.

Various iron oxide raw materials having different contents of P, B, S, and Cl are used, and the content in the sintered body sample is finally P: 50 massppm or less, B: 20 massppm or less, S: 30 massppm or less, and When calculated to contain Cl: 50 massppm or less and all Fe and Mn contained are converted as Fe ₂ O ₃ and MnO, Fe ₂ O ₃ : 49.0 mol%, ZnO: 20.0%, CoO: 2.0 mol The raw materials were weighed so as to have a composition of% and the balance MnO, mixed for 16 hours using a ball mill, and then calcined in air at 925 ° C. for 3 hours. Next, 0.005 mass% each of SrO and BaO is added to the calcined powder, pulverized with a ball mill for 12 hours, the resulting pulverized powder is granulated with polyvinyl alcohol, and a pressure of 118 MPa is applied. A toroidal core was molded. After that, the compact was placed in a firing furnace, fired at a maximum temperature of 1350 ° C, and cooled in the temperature range from 1100 ° C to 500 ° C in an industrial nitrogen stream with an oxygen partial pressure of 10 volppm. A sintered body sample having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm was obtained. For each of these samples, the Curie temperature was measured, and the normalized impedance was calculated from the impedance at 100 kHz and 20 MHz measured by applying a 10-turn winding.

  Table 2 shows the measurement results of the normalized impedance. The Curie temperature almost determined by the main component composition was 130 ° C. for all samples. From Table 2, the invention examples (Sample Nos. 1-5, 2-1) with P, B, S, and Cl components of less than 50, 20, 30 and 50 massppm, respectively, showed no abnormal grain growth and were normalized. An excellent impedance value of 2.5 Ω / mm or more at 100 kHz and 60 Ω / mm or more at 20 MHz was obtained. On the other hand, the occurrence of abnormal particles was confirmed in all of the comparative examples (sample numbers 2-2 to 2-7) including more than one appropriate value among the four components. For this reason, the values of normalized impedance are greatly deteriorated in both 100 kHz and 20 MHz.

To the calcined powder having the same composition as in Example 2 (however, P, B, S and Cl are all adjusted to less than 5 massppm), CaO and SiO ₂ are added as additive components so that the final composition has the ratio shown in Table 3. Then, it is pulverized for 12 hours in a ball mill, granulated by adding polyvinyl alcohol to this pulverized powder, and a toroidal core is formed by applying a pressure of 118 MPa. Firing at 1350 ° C, cooling in the temperature range from 1100 ° C to 500 ° C after firing in an industrial nitrogen flow with an oxygen partial pressure of 10 volppm, sintering with an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm Got a body core. For each of these samples, the Curie temperature was measured, and the normalized impedance was calculated from the impedance at 100 kHz and 20 MHz measured by applying a 10-turn winding.

The obtained measurement results are shown in Table 3. The Curie temperature determined by the main component composition was 130 ° C. for all samples. From Table 3, the normalized impedance at 20 MHz is improved in the invention examples (sample numbers 3-1 to 3-3) to which one or two kinds of CaO and SiO ₂ are added. However, in either of the comparative examples (sample numbers 3-4 to 3-6) including more than the appropriate value in either one, abnormal grain growth occurs and the normalized impedance is greatly deteriorated in both 100 kHz and 20 MHz.

The calcined powder having the same composition as in Example 2 (however, P, B, S and Cl are all adjusted to less than ₅ massppm), and Nb ₂ O ₅ , Ta ₂ O ₅ , HfO ₂ and ZrO ₂ are added as additive components, respectively. Add the composition to the ratio shown in Table 4, grind it with a ball mill for 12 hours, add polyvinyl alcohol to this pulverized powder, granulate, shape the toroidal core by applying a pressure of 118 MPa, and then The body was placed in a firing furnace, fired at a maximum temperature of 1350 ° C, and cooled in the temperature range from 1100 ° C to 500 ° C after firing in an industrial nitrogen flow with an oxygen partial pressure of 10 volppm. A sintered core of 15 mm and a height of 5 mm was obtained. For each of these samples, the Curie temperature was measured, and the normalized impedance was calculated from the impedance at 100 kHz and 20 MHz measured by applying a 10-turn winding.

The obtained measurement results are shown in Table 4. The Curie temperature determined by the main component composition was 130 ° C. for all samples. From the results in Table 4, all of the invention examples (sample numbers 4-1 to 4-15) to which one or more appropriate amounts of Nb ₂ O ₅ , Ta ₂ O ₅ , HfO ₂ and ZrO ₂ were added were crystalline. As a result of moderately suppressed growth, the normalized impedance at 20 MHz is improved. However, the comparative examples (sample numbers 4-16 to 4-18) containing one of these four components in excess of the appropriate range all generate abnormal grains and have normalized impedances of 100 kHz and 20 MHz. Both have deteriorated greatly.

Calcined powder having the same composition as in Example 2 (except, P, B, all S and Cl are adjusted to less than 5Massppm) to, as a secondary component, CaO, and SiO _2, further _{Nb 2 O 5, Ta 2 O} 5, Add HfO ₂ and ZrO _{2 so} that the final components are as shown in Table 5, pulverize with a ball mill for 12 hours, add polyvinyl alcohol to the obtained pulverized powder, granulate, and apply a pressure of 118 MPa. The toroidal core is then molded, and then the compact is placed in a firing furnace, fired at a maximum temperature of 1350 ° C, and cooled in the temperature range from 1100 ° C to 500 ° C for an oxygen partial pressure of 10 volppm. A sintered core having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm was obtained. For each of these samples, the Curie temperature was measured, and the normalized impedance was calculated from the impedance at 100 kHz and 20 MHz measured by applying a 10-turn winding. The Curie temperature determined by the main component composition was 130 ° C. for all samples.

  The obtained measurement results are shown in Table 5. The Curie temperature determined by the main component composition was 130 ° C. for all samples. As shown in Table 5, all of the inventive examples (sample numbers 5-1 to 5-9) added in the scope of the present invention in combination with the above six kinds of additive components were 20 MHz compared with the case where they were not added. The standardized impedance at has improved. On the other hand, in any of the comparative examples (sample numbers 5-10 to 5-11) containing any one of these six components in excess of the appropriate value, abnormal particles are generated and normalized at 100 kHz and 20 MHz. Both impedances are greatly degraded.

  The ferrite of the present invention can be used mainly as a magnetic core (core) of a noise filter used in various electric appliances as an electronic component.

Claims (3)

The basic components consist of Fe ₂ O ₃ : 45.0 to less than 50.0 mol%, CoO: 0.5 to 4.0 mol%, ZnO: 15.5 to 24.0 mol%, the balance MnO, and any one or two of SrO and BaO as additive components In the Mn-Co-Zn ferrite containing 0.001 to 0.050 mass% of seeds in total, the amounts of P, B, S and Cl contained in the ferrite are P: less than 50 massppm, B: less than 20 massppm, and S: 30 massppm, respectively. And Mn—Co—Zn ferrite characterized by being less than 50 massppm. 2. The Mn—Co—Zn system according to claim 1, further comprising any one or two of CaO: 0.005 to 0.200 mass% and SiO ₂ : 0.001 to 0.050 mass% as the additive component. Ferrite. As the additive component, ZrO ₂ : 0.005 to 0.100 mass%, Ta ₂ O ₅ : 0.005 to 0.100 mass%, HfO ₂ : 0.005 to 0.100 mass%, and Nb ₂ O ₅ : 0.005 to 0.100 mass% Or Mn-Co-Zn type ferrite of Claim 1 or 2 containing 2 or more types.