JP2019199379A - HEAT RESISTANCE AND HIGH MAGNETIC PERMEABILITY MnZn FERRITE - Google Patents

Abstract

To provide heat resistance high magnetic permeability MnZn ferrite that has less decrease of original high relative initial magnetic permeability even when using it at a high temperature environment equal to or higher than 100°C continuously for a long term.SOLUTION: The heat resistance high magnetic permeability MnZn ferrite is MnZn ferrite including FeO, ZnO and MnO as main constituents in such an amount that, in the main constituent of 100 mol%, has FeOof 50.50 to 54.00 mol%, ZnO of 11.00 to 18.00 mol%, and MnO of the remainder. The heat resistance high magnetic permeability MnZn ferrite includes, as accessory constituents, CoOof 0.10 to 0.55 pts.mass, SnOof 0.50 to 4.00 pts.mass, BiOof 0.001 to 0.030 pts.mass, MoOof 0.001 to 0.020 pts.mass, SiOof 0.001 to 0.010 pts.mass, and CaO of 0.015 to 0.030 pts.mass, based on 100 pts.mass of a total amount of the main constituent.SELECTED DRAWING: None

Description

  The present invention relates to a heat resistant high magnetic permeability MnZn ferrite.

In recent years, the need for CO ₂ emission reduction and energy saving has increased, and the in-vehicle devices such as hybrid vehicles and electric vehicles have been electrically equipped, and studies for clearing the noise regulations related to the in-vehicle devices are in progress.

  In particular, it has been clarified that common mode noise is generated from the inverter and the motor in the electric compressor, and the need for noise countermeasures using an AC line filter or the like is increasing.

  Conventionally, a common mode choke coil such as an AC line filter has been developed in order to suppress noise generated from a power supply line of a television or an air conditioner. In particular, in recent years, in order to increase the noise attenuation capability in the region from 150 kHz to several MHz, the magnetic permeability of the MnZn ferrite (sintered body) that becomes the magnetic core material (core) of the AC line filter is improved and the stability of the magnetic permeability with respect to frequency Development has been done to enhance.

  MnZn ferrite that has been developed as a magnetic core material for AC line filters so far mainly has a Curie temperature of about 120 ° C in order to increase the initial permeability near room temperature, and in a high temperature range exceeding this temperature. The function as a line filter was not able to be demonstrated by the use of the vehicle equipment etc. which are used.

  On the other hand, in Patent Document 1, the basic component composition of ferrite is controlled, and the amount of carbon remaining in the ferrite is suppressed to a predetermined value or less, thereby allowing the initial permeability at 10 kHz in a wide temperature range of −20 to 150 ° C. An Mn—Zn—Co based ferrite with increased magnetic susceptibility is disclosed. Further, Patent Document 2 discloses a Mn—Zn—Co based ferrite in which a trace amount of MgO is added and the amount of carbon remaining in the ferrite is suppressed to a predetermined value or less. These techniques are considered to be effective techniques for equipment used in a high temperature range.

JP2015-229626A JP2015-229625A

  On the other hand, in particular, electronic components used for in-vehicle use not only have temporary magnetic characteristics in a high temperature environment, but also maintain performance even when used continuously for a long time in a high temperature environment of, for example, 100 ° C. High durability is also required. However, until now, such durability has not been evaluated including the above patent documents.

  In view of the above problems, the present invention provides a heat-resistant and high-permeability MnZn ferrite with little decrease in initial high relative initial permeability even when used continuously for a long time in a high-temperature environment of 100 ° C. or higher. Objective.

The heat resistant high magnetic permeability MnZn ferrite according to the present invention is
MnZn ferrite mainly composed of Fe ₂ O ₃ , ZnO and MnO,
During the main component 100mol%, 50.50~54.00mol% of _Fe 2 _{O 3, 11.00~18.00mol%} of ZnO, in an amount which is a remainder of MnO,
When the total amount of the main component is 100 parts by mass, 0.10 to 0.55 parts by mass of Co ₂ O ₃ , 0.50 to 4.00 parts by mass of SnO ₂ and Bi ₂ O ₃ as subcomponents are used. 0.001 to 0.030 parts by mass, 0.001 to 0.020 part by weight of MoO _3, the SiO ₂ 0.001 to 0.010 parts by weight, and CaO containing 0.015 to 0.030 parts by weight It is characterized by that.

  ADVANTAGE OF THE INVENTION According to this invention, even when it uses continuously for a long period of time in a high temperature environment of 100 degreeC or more, it can provide the heat resistant high magnetic permeability MnZn ferrite with little fall of the initial high relative initial magnetic permeability.

Embodiments of the present invention will be described below. The MnZn ferrite according to the embodiment of the present invention includes Fe ₂ O ₃ (iron oxide (III)) and ZnO (zinc oxide) as main components after sintering, and the balance is substantially MnO (manganese oxide). It consists of Further, MnZn ferrite according to an embodiment of the present invention, as the additive, SiO ₂ (silicon dioxide), CaO (calcium oxide), MoO ₃ (molybdenum oxide), _Bi 2 _{O 3} (bismuth oxide), and _Co 2 O ₃ (cobalt oxide) and SnO ₂ (tin oxide).

(Curie temperature)
The MnZn ferrite according to the embodiment of the present invention will be described below. Since the MnZn ferrite according to the present embodiment is used as a magnetic core material such as an in-vehicle AC line filter, it is preferable to have a high Curie temperature of 170 to 235 ° C. so as to withstand continuous use for a long time in a high temperature environment. . Curie temperature is the temperature at which a ferromagnetic material changes to a paramagnetic material. In MnZn ferrite, the Curie temperature is substantially determined by the ratio of the main components Fe ₂ O ₃ , MnO, and ZnO. Therefore, MnZn ferrite having a Curie temperature of 170 to 235 ° C. can be obtained by appropriately combining these blending amounts.

Specifically, 50.50～54.00Mol% of _Fe 2 _{O 3} as a main component, ZnO and 11.00～18.00Mol%, by containing such that 100 mol% combined MnO as balance, An MnZn ferrite having a Curie temperature of 170 ° C. or higher and 235 ° C. or lower can be obtained. Fe ₂ O ₃ is more preferably 51.00 mol% or more and 53.00 mol% or less. ZnO is more preferably 15.00 mol% or more and 17.00 mol% or less.

By setting the content of Fe ₂ O ₃ to 50.50 mol% or more, a Curie temperature of 170 ° C. or more can be obtained. Further, the _Fe 2 _{O 3} is set to be lower than or equal 54.00Mol%, can be obtained more than 7,000 in a ratio initial permeability 10kHz~200kHz at 23 ° C. to 150 DEG ° C..

  Further, by setting the ZnO content to 11.00 mol% or more, it is possible to obtain 7000 or more with a relative initial permeability of 10 kHz to 200 kHz at 23 ° C. to 150 ° C. Moreover, Curie temperature 170 degreeC or more can be obtained by making ZnO 18.00 mol% or less.

  Since this MnZn ferrite has a Curie temperature of 170 ° C. or higher, it is possible to manufacture a line filter using a MnZn ferrite core that can be used for a long time in a high temperature environment of 100 ° C. or higher as a magnetic core.

  Hereinafter, subcomponents for improving the relative initial permeability will be described.

(Improvement of temperature dependence of relative initial permeability)
The MnZn ferrite preferably has a relative initial permeability as high as possible. For that purpose, it is preferable to have uniform and large crystal grains. Therefore, by combining Bi ₂ O ₃ that promotes crystal grain growth and MoO ₃ that promotes uniform crystal grain growth as a material, uniform and large crystal grains can be obtained, and high relative initial permeability can be obtained. Furthermore, by containing Co ₂ O ₃ , the temperature dependence of the magnetocrystalline anisotropy can be suppressed to a small value, and a high specific initial permeability (7000 or more) can be obtained in a wide temperature range (23 to 150 ° C.). By appropriately combining the blending amounts of these materials, MnZn ferrite having a high relative initial permeability over a wide temperature range can be obtained.

Specifically, in the above MnZn ferrite, when the total amount of Fe ₂ O ₃ , MnO, and ZnO as main components is 100 parts by mass, Bi ₂ O ₃ is 0.001 to 0.030 mass as an accessory component. 7000 or more can be obtained as a relative initial permeability of 10 kHz at 23 to 150 ° C. by containing 0.001 to 0.020 parts by mass of MoO ₃ . Furthermore, the temperature dependence of the relative initial permeability can be suppressed by containing 0.10 to 0.55 parts by mass of Co ₂ O ₃ . Incidentally, _Bi 2 _{O 3} is more preferably 0.005 to 0.020 parts by weight. MoO ₃ is more preferably 0.001 to 0.010 parts by mass. Co ₂ O ₃ is more preferably 0.20 to 0.40 parts by mass.

By controlling the content of Bi ₂ O ₃ to 0.030 parts by mass or less, it is possible to suppress the generation of a large amount of coarse crystal grains, to suppress non-uniformity of the crystal grain size, and to increase the initial permeability while increasing the ferrite permeability. In order to suppress the deterioration of the frequency characteristics, a relative initial permeability of 7000 or more can be obtained even at 200 kHz. Further, by setting the _Bi 2 _{O 3} and 0.001 parts by mass or more, grain growth of the core center portion is performed sufficiently, it is possible to obtain more than 7,000 in a ratio initial permeability 10 kHz.

By containing 0.001 part by mass or more of MoO ₃ , a sintered body having a uniform crystal grain size can be obtained, the frequency characteristics can be improved, and a relative initial permeability of 7000 or more can be obtained even at 200 kHz. Further, by making the MoO ₃ than 0.020 parts by mass, grain growth of the core center portion is performed sufficiently, it is possible to obtain more than 7,000 in a ratio initial permeability 10 kHz.

By containing Co ₂ O ₃ in an amount of 0.10 parts by mass or more and 0.55 parts by mass or less, the temperature dependence of the relative initial permeability is suppressed, and a relative initial permeability of 7000 or more is obtained at 23 ° C. to 150 ° C. Can do.

  Since this MnZn ferrite has a high relative initial magnetic permeability (7000 or more) over a wide temperature range (23 to 150 ° C.), a line filter with the same size and higher performance as the line filter using the conventional MnZn ferrite is manufactured. can do. Alternatively, a smaller line filter having the same performance as the conventional one can be manufactured.

(Improvement of frequency dependence of relative initial permeability)
MnZn ferrite suppresses generation of eddy currents in a high frequency region by forming a crystal grain boundary having high specific resistance due to SiO ₂ and CaO, and has a high relative initial permeability (7000 or more) up to a high frequency region (˜200 kHz). ) Can be kept. Further, when a core is wound and used as a magnetic core of a line filter, it can have a large noise attenuation capability (impedance) in a frequency band (150 kHz to 1 MHz vicinity) considered to be particularly important.

Specifically, in the MnZn ferrite, when the total amount of the main components is 100 parts by mass, 0.002 to 0.010 parts by mass of SiO ₂ and 0.015 to 0.030 parts by mass of CaO are contained as subcomponents. By doing so, a relative initial permeability of 7000 or more can be obtained in a frequency range of 10 kHz to 200 kHz. Incidentally, it is more preferable SiO ₂ is 0.003 to 0.006 parts by weight. CaO is more preferably 0.018 to 0.023 parts by mass.

By containing 0.001 part by mass or more of SiO ₂ , the deterioration of the frequency characteristic of the magnetic permeability can be suppressed, and a relative initial magnetic permeability of 7000 or more can be obtained even at 200 kHz. Further, by the SiO ₂ and not more than 0.010 part by weight, it is possible that the value of the ratio initial permeability at 10kHz get more 7000.

  Further, by containing 0.015 parts by mass or more of CaO, it is possible to suppress deterioration of the frequency characteristics of the magnetic permeability, and to obtain a relative initial magnetic permeability of 7000 or more even at 200 kHz. Moreover, the value of the relative initial permeability at 10 kHz can be 7000 or more by setting CaO to 0.030 parts by mass or less.

  Such MnZn ferrite has a large noise attenuation capability (impedance) in a frequency band (around 150 kHz to 1 MHz) that is considered particularly important when it is molded into a core, wound, and used as a magnetic core of a line filter. . That is, the ability to reduce noise is greater than that of a line filter using MnZn ferrite of the prior art.

(Improved heat resistance)
When MnZn ferrite containing 50 mol% or more of Fe ₂ O ₃ is left in a high temperature environment such as 150 ° C., for example, metal ions (Fe ²⁺ and Co ²⁺ ) begin to diffuse into the vacancies, and the vacancies gradually move around the domain wall. It is considered that the domain wall becomes difficult to move and the relative permeability is lowered.

In order to suppress this phenomenon, it is considered effective to reduce metal ions (Fe ²⁺ , Co ²⁺ ) in ferrite or to reduce vacancies. In order to reduce Fe ²⁺ , it is considered effective to make Fe ₂ O ₃ 50 mol% or less, but the problem arises that the relative permeability and the Curie temperature are lowered. Moreover, if the content of Co ₂ O ₃ is reduced in order to reduce Co ²⁺ , the temperature dependency of the relative permeability is deteriorated. Moreover, it is considered effective to reduce the oxygen concentration in the sintering process to reduce the vacancies, but in order to maintain a high relative permeability up to a high frequency region of about 200 kHz, the specific resistance of the ferrite sintered body should be reduced. In order to improve it, it is necessary to raise the oxygen concentration moderately and form a high-resistance crystal grain boundary, and it is difficult to completely eliminate vacancies.

The inventors considered that it would be effective to incorporate metal ions other than Fe ²⁺ and Co ^{2+ in} order to reduce vacancies without reducing the oxygen concentration during sintering, and as a result of conducting various studies, In MnZn ferrite containing Co ₂ O ₃ and containing 50 mol% or more of Fe ₂ O ₃ , it has been found that by containing an appropriate amount of SnO ₂ , a decrease in the relative permeability after being left in a high temperature environment can be suppressed. .

Specifically, in the above MnZn ferrite, when the total amount of the main component is 100 parts by mass, by containing 0.50 to 4.00 parts by mass of SnO ₂ as an auxiliary component, 1000 hours in an environment of 150 ° C. It was found that the rate of change of the relative initial permeability at 10 kHz at 120 ° C. after being allowed to stand before being allowed to stand can be suppressed to 35% or less as an absolute value. Incidentally, it is more preferably SnO ₂ is from 1.50 to 2.50 parts by weight.

By containing SnO ₂ in an amount of 0.50 parts by mass or more, the relative initial permeability at 120 ° C. after being allowed to stand for 1000 hours in an environment at 150 ° C. is 35% or less as an absolute value compared to the relative initial permeability before being left as it is. It can be. Further, by making the SnO ₂ than 4.00 part by weight, it is possible to obtain a specific initial permeability 7000 or more at 23 ° C. to 150 DEG ° C..

  Such MnZn ferrite can provide a line filter with little deterioration in characteristics such as relative initial permeability due to changes over time even in a situation where the use is continued for a long time in an in-vehicle environment of 100 ° C. or higher.

As described above, Fe ₂ O ₃ , ZnO, and MnO are the main components and Co ₂ O ₃ , SnO ₂ , Bi ₂ O ₃ , MoO ₃ , SiO ₂ , and CaO are contained in a predetermined range as subcomponents. Thus, the Curie temperature is 170 ° C. or higher, the relative initial permeability is as high as 7000 or higher in a wide frequency range of 10 kHz to 200 kHz in the temperature range of 23 to 150 ° C., and 120 even after being left for 1000 hours in an environment of 150 ° C. It is possible to obtain a high magnetic permeability MnZn ferrite having excellent heat resistance characteristics such that there is little decrease in the relative initial magnetic permeability at ° C.

(Production method)
Next, an embodiment of a method for producing MnZn ferrite will be described.
The manufacturing method of the MnZn ferrite core of the present embodiment includes a mixing process, a drying / granulating process, a calcining process, a crushing process, a drying / granulating process, a molding process, and a sintering process.

Fe ₂ O ₃ content after sintering is 50.50 mol% or more and 54.00 mol% or less, ZnO content is 11.00 mol% or more and 18.00 mol% or less, and the balance is 100 mol% as MnO in total. In addition, in the mixing step, each raw material powder of the main component so that Fe ₂ O ₃ is 49.30 mol% or more and 52.80 mol% or less, ZnO is 11.60 mol% or more and 18.60 mol% or less, and the balance is MnO. Weigh. Next, all raw material powders are mixed and pulverized to obtain a mixed powder. Specifically, the agglomerated raw material powder is pulverized and mixed using an attritor or the like until the median diameter D50 of the mixed powder is 0.5 μm or more and 0.9 μm or less. The particle size distribution of the mixed powder can be measured with a particle size distribution measuring device.

  In the drying and granulation step, 0.5 to 1 part by weight of a binder such as polyvinyl alcohol is added to the mixed powder obtained in the mixing step when the total weight of the mixed powder is 100 parts by weight. Use to spray to obtain granules.

  In the calcining step, the granule obtained in the drying / granulating step is calcined at, for example, 750 ° C. for 1 hour in an air atmosphere to obtain a calcined product.

In the crushing step, when the total mass of the obtained calcined product (main component) is 100 parts by mass, 0.001 to 0.010 part by mass of SiO ₂ is added to the calcined product. Here, it is preferable amount of SiO ₂ is 0.003 to 0.006 parts by weight. Moreover, 0.019-0.040 mass part Ca (OH) ₂ is added to a calcined product so that CaO content after sintering may be 0.015-0.030 mass part. Furthermore, when the total mass of the calcined product is 100 parts by mass, the required amount of MoO ₃ is added to the calcined product so that the MoO ₃ content after sintering is 0.001 to 0.020 part by mass. Since a part of MoO ₃ is volatilized in the sintering step, a required amount larger than the desired content after sintering is added. The required amount of MoO ₃ is, for example, 0.1 parts by mass or less.

Bi ₂ O ₃ has the effect of growing crystal grains by adding to ferrite, but also has the effect of making the crystal grain size non-uniform, so when the total mass of the calcined product is 100 parts by mass It is desirable to add 0.001 to 0.030 parts by mass to the calcined product. Further, when the total mass of the calcined product is 100 parts by mass so that the content of Co ₂ O ₃ after sintering is 0.10 to 0.55 parts by mass, 0.09 to 0.54 parts by mass Co ₃ O ₄ is added to the calcined product. Further, when the total mass of the calcined product is 100 parts by mass, 0.50 to 4.00 parts by mass of SnO ₂ is added.

  After each additive is added, the calcined product is crushed to obtain a crushed powder. Specifically, in the crushing step, the calcined product is crushed until the median diameter D50 of the crushed particle size is 0.5 μm or more and 1.0 μm or less to obtain a crushed powder.

  In the drying / granulation process, when the total mass of the pulverized powder is 100 parts by mass to the pulverized powder obtained in the pulverization process, 0.5 to 1.0 parts by mass of a binder such as polyvinyl alcohol is added. Granules are obtained by spraying with a spray dryer or the like. At this time, the median diameter D50 of the granules is preferably 80 μm or more and 200 μm or less.

  In the molding step, the granules obtained in the drying / granulation step are molded into a toroidal core having a predetermined shape, for example, an outer diameter of 19 mm, an inner diameter of 13 mm, and a height of 11 mm.

  In the sintering step, for example, a sintered body is obtained by sintering at 1300 ° C. for a predetermined time.

  Next, examples will be described. In the examples, a MnZn ferrite core was prepared using a raw material containing a predetermined amount of a predetermined component, and its characteristics were evaluated. First, the ferrite core used for property evaluation will be described. The ferrite cores produced in the examples of the present invention and the comparative examples are toroidal ferrite cores having an outer diameter of 19 mm, an inner diameter of 13 mm, and a height of 11 mm. An evaluation sample was prepared by winding a copper wire having a wire diameter of 0.26 mm around this ferrite core 10 times, and the relative initial permeability was measured using an impedance analyzer (4194A, manufactured by Yokogawa Hewlett-Packard Company). The current value at the time of measurement was 0.2 mA.

Example 1
_Fe 2 _{O 3} content 50.50Mol% after sintering, 16.00Mol% ZnO, the content, as MnO content is the total 100 mol% as 33.50Mol%, in the mixing step, _Fe 2 _{O 3} Each raw material powder was weighed and mixed so that the total amount was 100 mol%, with 49.30 mol% of Zn, 16.60 mol% of ZnO, and 34.10 mol% of Mn ₃ O ₄ in terms of MnO. In the mixing step, the mixture was pulverized with an attritor until the median diameter D50 of the mixture became 0.5 μm or more and 0.9 μm or less. Next, in the drying and granulation step, 0.5 parts by mass of polyvinyl alcohol was added when the total mass of the mixture was 100 parts by mass, and the mixture was sprayed with a spray dryer to obtain granules. Next, as a calcining step, this was calcined at 750 ° C. for 1 hour in an air atmosphere to obtain a calcined product.

When the total mass of the obtained calcined product was 100 parts by mass, 0.004 part by mass of SiO ₂ was added to the calcined product. Similarly, 0.028 parts by mass of Ca (OH) ₂ and MoO ₃ are 0.075 parts by mass, and Bi ₂ O ₃ is 0.00 parts by mass so that the CaO content after sintering is 0.021 parts by mass. When the total mass of the calcined product is 100 parts by mass so that the content of Co ₂ O ₃ after sintering is 0.29 parts by mass, 0.28 parts by mass of Co ₃ O ₄ , SnO ₂ was added to the calcined product at 2.00 parts by mass.

  Next, as a crushing step, the mixture of the calcined product and the additive is crushed with a crusher so that the median diameter D50 of the crushed particle size is 0.5 μm or more and 1.0 μm or less, and then crushed powder Got. Next, as a drying / granulating step, when the total mass of the crushed material was 100 parts by mass, 1 part by mass of polyvinyl alcohol was added to the crushed material and sprayed with a spray dryer to obtain granules. The median diameter D50 of the granules at this time was 110 μm. Next, as a forming step and a sintering step, the granules were formed into a toroidal core having an outer diameter of 19 mm, an inner diameter of 13 mm, and a height of 11 mm, and sintered at 1300 ° C. to obtain a sintered body. The above manufacturing process until the sintered body is obtained is the same as the manufacturing process of the ferrite core in the prior art.

  The relative initial permeability (23 ° C.) of this ferrite core was 7200 at 10 kHz and 7300 at 200 kHz. The Curie temperature was 171 ° C. The ferrite core was left in a thermostatic chamber (air atmosphere) at 150 ° C. for 1000 hours, and the relative initial permeability at 10 kHz at 120 ° C. before and after being left was measured to determine the rate of change. As a result of measuring the relative initial permeability as described above, the change rate of the relative initial permeability at 10 kHz was −24.0%. The rate of change was calculated by ((Relative initial permeability at 120 ° C. after standing−Relative initial permeability at 120 ° C. before standing) / Relative initial permeability at 120 ° C. before standing) × 100 (%).

  In the same manner as above, the properties of the ferrite cores of Examples 2 to 16 and Comparative Examples 1 to 16 were measured with the compositions shown in Table 1. The results are shown in Table 1.

  As shown in Table 1, by producing a MnZn ferrite core using a material having a composition within the range of the present invention, the relative initial permeability (23 ° C.) is 7000 at a Curie temperature of 170 ° C. or higher and 10 kHz to 200 kHz. As described above, an MnZn ferrite core in which the rate of change in relative initial permeability at 10 kHz at 120 ° C. before and after being left for 1000 hours in an environment at 150 ° C. was 35% or less as an absolute value could be obtained.

In particular, it can be seen from Example 1-4 and Comparative Example 1-4 that it is important to keep Fe ₂ O ₃ , ZnO, and MnO within a predetermined range in order to set the Curie temperature to 170-235 ° C. . Further, from Example 5-12 and Comparative Example 5-12, in order to increase the relative initial permeability (23 ° C.) to 7000 or more, SiO ₂ , CaO, MoO ₃ and Bi ₂ O ₃ are set within a predetermined range. It turns out that is important. Also, from Example 13-16 and Comparative Example 13-16, in order for the rate of change of the relative initial permeability at 120 ° C. before and after being left in a 150 ° C. environment for 1000 hours to be 35% or less as an absolute value, It can be seen that it is important to keep Co ₂ O ₃ and SnO ₂ within a predetermined range.

Claims (5)

MnZn ferrite mainly composed of Fe ₂ O ₃ , ZnO and MnO,
During the main component 100mol%, 50.50~54.00mol% of _Fe 2 _{O 3, 11.00~18.00mol%} of ZnO, in an amount which is a remainder of MnO,
When the total amount of the main component is 100 parts by mass, 0.10 to 0.55 parts by mass of Co ₂ O ₃ , 0.50 to 4.00 parts by mass of SnO ₂ and Bi ₂ O ₃ as subcomponents are used. 0.001 to 0.030 parts by mass, 0.001 to 0.020 part by weight of MoO _3, the SiO ₂ 0.001 to 0.010 parts by weight, and CaO containing 0.015 to 0.030 parts by weight A heat-resistant high magnetic permeability MnZn ferrite characterized by the above. _2. The heat resistant high magnetic permeability MnZn ferrite according to claim 1, comprising 0.20 to 0.40 parts by mass of Co ₂ O ₃ and 1.50 to 2.50 parts by mass of SnO ₂ . The heat-resistant high magnetic permeability MnZn according to claim 1 or 2, wherein 0.002 to 0.020 parts by mass of Bi ₂ O ₃ and 0.001 to 0.010 parts by mass of MoO ₃ are contained. Ferrite. The heat resistant high permeability according to any one of claims 1 to 3, comprising 0.003 to 0.006 parts by mass of the SiO ₂ and 0.018 to 0.023 parts by mass of the CaO. Magnetic susceptibility MnZn ferrite.   5. The rate of change in relative initial permeability at 10 kHz at 120 ° C. before and after being left in a 150 ° C. environment for 1000 hours is absolute, including the heat-resistant high magnetic permeability MnZn ferrite according to claim 1. A MnZn ferrite core for a line filter having a value of 35% or less.