JP5883835B2 - Mn-Zn-Ni ferrite and method for producing the same - Google Patents

Description

  The present invention is suitable for use in magnetic cores such as Mn-Zn-Ni ferrites with low energy loss, especially switching power supply transformers. For example, high saturation magnetic flux density and low iron loss in a high temperature region of 150 ° C. or higher. This relates to the Mn-Zn-Ni ferrite shown.

  Oxide magnetic materials are generally referred to as ferrite, and this ferrite is classified into hard magnetic materials such as Ba-based ferrite and Sr-based ferrite and soft magnetic materials such as Mn-Zn-based ferrite and Ni-Zn-based ferrite. . A soft magnetic material is a material that is sufficiently magnetized even with a very small magnetic field, and is used in a wide range of fields such as power supplies, communication devices, measurement control devices, magnetic recording, and computers. Properties required for the soft magnetic material include a low coercivity, a high magnetic permeability, a high saturation magnetic flux density, and a low iron loss.

  As the soft magnetic material, in addition to the oxide ferrite, there are metal materials. Metallic soft magnetic materials are characterized by a higher saturation magnetic flux density than oxide-based materials, but they have low electrical resistance, and when used in a high frequency range, iron loss due to eddy currents increases. . Therefore, in recent years when the frequency of use has been increased due to the demand for miniaturization and high density of electronic devices, conventional metal materials are used in the high frequency band of about 100 kHz or more used for switching power supplies. That is almost impossible.

  Against this background, Mn-Zn ferrite that generates less heat is mainly used as the magnetic core material for power transformers in the high frequency range. However, since this material also has an electrical resistivity value of about 0.01 to 0.05 Ω · m, by further increasing the electrical resistance and reducing eddy current loss, the overall iron loss is reduced and the amount of heat generated is reduced. It was hoped to suppress it.

In response to this problem, for example, in Patent Document 1, a small amount of an oxide such as SiO ₂ or CaO is added as an accessory component to Mn-Zn ferrite and segregated at the grain boundary to increase the grain boundary resistance. A technique for suppressing heat generation by increasing the resistivity to several Ω · m or more is disclosed.

  Also, when used in a power transformer, consideration must be given to the temperature in the built-in equipment (operating temperature) and the temperature rise caused by the heat generated by the iron loss of the transformer material itself. For example, when the temperature at which the iron loss is minimized (hereinafter also referred to as the minimum iron loss temperature) is near room temperature, the iron loss increases due to the rise in the temperature of the magnetic core due to heat generation, and the heat generation further increases accordingly. There is a risk of causing a so-called thermal runaway that repeats this and accelerates the temperature rise. The operating temperature of the transformer is usually around 50 to 70 ° C. To avoid this risk, the current material has a temperature at which the iron loss becomes a minimum of about 100 ° C. The material is designed such that the coefficient is negative and the iron loss decreases with increasing temperature. However, in the case of a material having a minimum iron loss temperature of about 100 ° C., if the temperature rises to 100 ° C. or higher for some reason, the iron loss also increases, so there is a very high risk of thermal runaway.

  Furthermore, recently, in order to cope with the downsizing of electronic devices, the loading density of electronic components has increased, and the temperature rise due to heat generation tends to increase. In addition, parts used in recent electronic automobile applications such as hybrid cars, when placed near the engine, for example, high temperature range that has not been assumed so far, such as exceeding 100 ° C and 150-160 ° C It is forced to work with. Accordingly, there is a need to change the design operating temperature from about 100 ° C. to 150 ° C. or higher so that it can be operated in a high temperature range of about 150 to 160 ° C. For this purpose, the temperature dependence of the iron loss of the ferrite core needs to be compatible with these designs.

  Even when the minimum iron loss temperature is set to about 150 to 160 ° C so that it operates in a high temperature range, the saturation magnetic flux density decreases as the temperature rises. The designed value cannot be maintained, and the design change such as increasing the core shape and the problem of cost increase occur accordingly. The saturation magnetic flux density at 100 ° C. of a conventional low-loss material for transformers is 380 to 400 mT for a general-purpose material, but decreases to about 320 to 350 mT at 150 ° C. Therefore, when changing to a design that operates in a high temperature range of about 150 to 160 ° C., there is a great demand to maintain the saturation magnetic flux density at about 400 mT or more, which is the same as the value at 100 ° C. of the conventional material. .

  By the way, as a factor governing the iron loss, there is a magnetic anisotropy constant K1, and the iron loss changes with a temperature change of the magnetic anisotropy constant K1, and becomes a minimum at a temperature where K1 = 0. Therefore, in order to change the temperature dependence of the iron loss, it is necessary to change the temperature dependence of the magnetic anisotropy constant and its absolute value. In the case of Mn-Zn ferrite, the temperature dependence of the magnetic anisotropy constant can be reduced by introducing Co ions, and the absolute value of the iron loss temperature coefficient can be reduced (for example, Non-Patent Documents 1 and 2). reference). As a result, a material having a small iron loss in the vicinity of 100 ° C. and a relatively small iron loss in the temperature range before and after that can be obtained. However, by adding CoO, there is a problem that the iron loss minimum temperature decreases or the iron loss temperature coefficient and the minimum temperature fluctuate greatly due to slight fluctuations in the firing temperature and the oxygen concentration of the firing atmosphere. ing.

Here, Patent Document 2 discloses that Mn—Zn—Co based ferrite containing Fe ₂ O ₃ , ZnO, and MnO as main components and containing less than 0.01 to 0.5 mol% of CoO has a wider temperature range than conventional K1. Therefore, it is disclosed that high magnetic permeability and low iron loss are realized in a wide temperature range. However, in the technique of Patent Document 2, as shown in FIG. 1 of the same document, the minimum temperature of the iron loss shifts to a considerably low temperature side, the iron loss value near the maximum operating temperature increases, and the temperature rises. The danger of accelerating has not been resolved.

  In any of the techniques described in the above-mentioned documents, the temperature at which the minimum value of power loss is 100 ° C. or lower is disclosed, and no means is disclosed for transferring the minimum value of iron loss to a high temperature range of 150 ° C. to 160 ° C. Not. Also, even if the iron loss minimum temperature reaches a high temperature of 150 ° C or higher, the saturation magnetic flux density decreases as this iron loss minimum temperature shifts to a higher temperature, and the iron loss absolute value at that minimum temperature increases. To do is left as a problem. For this reason, even if thermal runaway at 150 ° C. or higher is suppressed, there is a disadvantage that the critical loss value increases and the fever problem cannot be solved.

Japanese Patent Publication No. 36-2283 Japanese Patent Publication No. 4-33755

`` The Effect of Cobalt subusutitutions on some properties of manganese zinc ferrites '', A.D.Giles and F.F.Westendorp: J.Phys.D: Appl.Phys., 9 (1976) 2117 `` Low-loss Power Ferrites for frequencies up to 500kHz '', T.G.W.Stijintjes And J.J.Roelofsma; Adv.Cer.16 (1986) 493

  The present invention has been made in view of the situation in which recent electronic components have come to be used in a high temperature range of 150 to 170 ° C. exceeding 100 ° C., which has not been assumed so far. Provides a Mn-Zn-Ni-based ferrite material in which a minimum value of iron loss exists in a high temperature region of, for example, 150 to 160 ° C, the value is small, and the saturation magnetic flux density is high in a high temperature region of 150 ° C or higher There is.

In order to solve the above-mentioned problems of the prior art, the inventors investigated the effect of the basic components Fe ₂ O ₃ and ZnO on the iron loss and its minimum temperature, and contained it as an additive. The effects of the various metal oxides on the saturation magnetic flux density and iron loss in the temperature range of 100 ° C. and higher of the final core have been studied. As a result, the iron loss minimum temperature and the saturation magnetic flux density differ depending on the composition range of the basic component, so Fe ₂ O ₃ and ZnO and MnO and NiO are added to the basic composition, and the composition range is narrowed down, according to the range By selecting the optimal additive and its content, it is possible to maintain a high saturation magnetic flux density in a high temperature range of 150 ° C. or higher and to obtain a low-loss ferrite, and to further reduce the amount of carbon entering as an unavoidable impurity. The inventors have found that the effect can be further improved by suppressing it within the range of the predetermined value, and have completed the present invention.

That is, the gist configuration of the present invention is as follows.
(1) Fe ₂ O ₃ : 54.0-55.0 mol%,
ZnO: 5.0 to 10.0 mol%,
NiO: 0.1 to 0.2 mol% and the balance MnO as basic components,
For the basic component,
SiO ₂ : 50 to 500 massppm,
CaO: 200-2000 massppm,
Nb ₂ O ₅ : 50-500 massppm and
BeO: 10-100 massppm
Is an Mn-Zn-Ni based ferrite consisting of inevitable impurities,
The Mn-Zn-Ni ferrite, wherein the carbon content in the inevitable impurities is suppressed to 50 massppm or less.

(2) Saturation magnetic flux density at 150 ° C and magnetizing force 1200A / m is 380mT or more, iron loss minimum temperature at maximum magnetic flux density 200mT and frequency 100kHz is 150-170 ° C, and iron loss at 160 ° C is 450kw / m ³ or less The Mn—Zn—Ni-based ferrite according to (1) above, wherein

(3) Oxide raw materials are weighed according to the basic component composition, mixed, calcined, then added with auxiliary components, mixed, further molded after pulverization, and the molded product is heated to a firing holding temperature. In the method for producing the Mn-Zn-Ni-based ferrite according to (1) or (2) by firing at
CaO as an accessory component is added as a Ca compound that does not contain carbon,
A method for producing an Mn—Zn—Ni-based ferrite, characterized in that an oxygen concentration in an atmosphere from 400 ° C. to a firing holding temperature is set to 5% by volume or more when the temperature is raised.

  According to the present invention, it is possible to provide an Mn—Zn—Ni ferrite having a high saturation magnetic flux density and a low iron loss in a high temperature range of 150 ° C. or higher. The ferrite of the present invention is suitable for use in a transformer core material such as a switching power supply.

From the viewpoint of optimizing the saturation magnetic flux density, the Curie temperature, and the minimum temperature of iron loss, the basic components of the Mn—Zn—Ni ferrite of the present invention are Fe ₂ O ₃ : 54.0 to 55.0 mol%, ZnO: It shall consist of 5.0 to 10.0 mol%, NiO: 0.01 to 0.1 mol% and the balance MnO.
The reason for limiting each component to the said range is demonstrated concretely below.

Fe ₂ O ₃ : 54.0 to 55.0 mol%
Fe ₂ O ₃ needs to have a minimum iron loss temperature of 150 ° C. or higher and 54.0 mol% or higher in order to maintain a high saturation magnetic flux density of 150 ° C. However, if it exceeds 55.0 mol%, the iron loss rises near room temperature, so the upper limit is made 55.0 mol%. Preferably, it is the range of 54.0-54.5 mol%.

ZnO: 5.0 to 10.0 mol%
As described above, the magnetic properties required for soft magnetic ferrite include a high saturation magnetic flux density, a high Curie temperature, a low iron loss, and a high magnetic permeability. Of these, the saturation magnetic flux density and the Curie temperature are substantially determined by the ratio of the basic components MnO, ZnO, and Fe ₂ O ₃ .
First, in a region where the amount of ZnO is relatively small, the saturation magnetic flux density at room temperature increases monotonously as the amount of ZnO increases, but the Curie temperature also decreases. In order to maintain a high saturation magnetic flux density in a high temperature range of about 150 ° C., it is important to increase the Curie temperature. Therefore, it is necessary to determine the ZnO amount in balance with the Curie temperature. That is, when the ZnO content is less than 5.0 mol%, the Curie temperature is high but the saturation magnetic flux density is still low, the iron loss value is considerably high, and the magnetic permeability is also low. On the other hand, when the amount of ZnO is more than 10.0 mol%, the saturation magnetic flux density at 150 ° C. decreases to 380 mT or less. Therefore, in order to maintain the saturation magnetic flux density at about 150 ° C. at 380 mT or more and the iron loss minimum temperature to 150 to 170 ° C., the ZnO content is set in the range of 5.0 to 10.0 mol%. In order to obtain a higher saturation magnetic flux density and a Curie point, a range of 6.0 to 9.0 mol% is preferable.

NiO: 0.1-0.2mol%
When the minimum iron loss temperature is set to 150 ° C or higher, and the composition of Fe ₂ O ₃ and ZnO is maintained as described above in order to maintain a high saturation magnetic flux density of 150 ° C, the iron loss value increases from other composition ranges. It was unavoidable that NiO was effectively added as a basic composition in the range of 0.1 to 0.2 mol% in order to suppress the increase in the iron loss value. In other words, NiO constitutes the spinel phase of Mn-Zn ferrite and affects the magnetic anisotropy together with Zn and Mn elements and contributes to realizing high saturation magnetic flux density and low loss. As a result of various studies on this point, it is 0.1 mol% or more that exerts the effect under the above-described Fe ₂ O ₃ and ZnO composition, and the low loss when the iron loss minimum temperature is 150 to 170 ° C. is 0.2%. Since it is up to mol%, the range of NiO is 0.1 to 0.2 mol%. Preferably, it is the range of 0.15-0.19 mol%.

The ferrite of the present invention is a quaternary ferrite of Fe ₂ O ₃ —ZnO—MnO—NiO, and the remaining basic component other than Fe ₂ O ₃ , ZnO and NiO is MnO. The amount of MnO is preferably in the range of 35 to 42 mol%. Note that the total of Fe ₂ O ₃ , ZnO, NiO and MnO is 100 mol%.

In addition to the above basic components, the ferrite of the present invention needs to add the following components as subcomponents. That is, Fe ₂ O ₃ , ZnO, MnO and NiO, which are the basic components of the ferrite of the present invention, form a spinel structure, and do not form a spinel, SiO ₂ , CaO and Nb ₂ O ₅ , and By adding a small amount of BeO, a high-performance Mn-Zn-Ni ferrite material with low iron loss can be obtained. Among these, the combined addition of SiO ₂ , CaO, Nb ₂ O ₅ and BeO is effective, and the action is as follows.

SiO ₂ : 50 to 500 massppm
CaO: 200-2000massppm
SiO ₂ forms a grain boundary with CaO, increases the resistance of the grain boundary, and contributes to a reduction in iron loss. However, if the addition amount is less than 50 massppm, the contribution is small, and if it exceeds 500 massppm, abnormal grain growth occurs during sintering, and the iron loss is greatly increased. CaO also contributes to lowering the iron loss by increasing the grain boundary resistance when coexisting with SiO ₂ , but the effect is small when the addition amount is less than 200 massppm, and the iron loss increases conversely when it exceeds 2000 massppm. Therefore, the addition amount of SiO ₂ and CaO is SiO _2: 50～500Massppm and CaO: preferably added in an amount of 200～2000Massppm. In order to obtain a lower loss, SiO ₂ : 50 to 300 massppm, CaO: 200 to 1500 massppm are preferable.

Nb ₂ O ₅ : 50-500 massppm
Nb ₂ O ₅ effectively contributes to the increase in specific resistance in the presence of SiO ₂ and CaO. However, if the content is less than 50 massppm, the addition effect is poor, whereas if it exceeds 500 massppm, the iron loss is reversed. Increase. Therefore, Nb ₂ O ₅ is added in the range of 50 to 500 massppm. In order to obtain a lower loss, the range of 50 to 300 massppm is preferable.

BeO: 10-100 massppm
BeO is an effective component for stably realizing low iron loss in a high temperature range of 150 ° C. or higher. Although the mechanism by which BeO addition affects the magnetic properties of the final sintered body has not yet been clearly clarified, BeO is an oxide having a high specific resistance and low dielectric constant and dielectric loss. It is considered that it has a positive effect on the properties of the final sintered body, particularly the iron loss on the high temperature side of 150 ° C. or higher. If the addition amount is less than 10 massppm, the effect cannot be obtained. If the addition amount is more than 100 massppm, abnormal grain growth is caused and the iron loss is greatly increased. Therefore, BeO is added in the range of 10 to 100 massppm.

As described above, it is possible to determine the composition range of the basic components Fe ₂ O ₃ , ZnO, MnO and NiO and to add SiO ₂ , CaO, Nb ₂ O ₅ and BeO in combination as subcomponents is important. Furthermore, it has been found that in order to stably realize low iron loss at a high temperature range of 150 ° C. or higher, it is effective to contain carbon (C) as an impurity within an appropriate range.

  That is, the impurity carbon (C) is inevitably mixed in the ferrite manufacturing process, and is included as residual C even after firing. As a result of various studies on the relationship between the residual C amount and the iron loss, new knowledge has been obtained that if the C amount is 50 massppm or less, it is effective in improving the iron loss in the frequency band up to 100 kHz. The reason why the amount of residual C affects the iron loss has not been fully elucidated, but if C is in the crystal grains, it will hinder the domain wall movement and increase the iron loss, and the grain boundary If it breaks down, it becomes the core for imparting conductivity, reducing the specific resistance when using ferrite as the core in the high frequency range, and as a result, eddy current loss increases, affecting iron loss on the high temperature side of 150 ° C or higher It is thought that it exerts.

  Specifically, it is necessary to suppress the carbon content in the inevitable impurities to 50 massppm or less. That is, if the carbon content exceeds 50 massppm, the effect of improving the iron loss value is lost, and if it is 50 massppm or less, the iron loss value is sufficiently improved as compared with the conventional material. In addition to the above-mentioned C, other impurities include (chlorine Cl, sulfur S) and the like, but these have no problem in terms of characteristics if the total amount mixed is 0.01% by mass or less.

Here, C mixed in the ferrite manufacturing process includes (i) C contained in the main raw materials of Nb ₂ O ₅ , MnO and ZnO, (ii) C contained in various additives of the auxiliary raw materials, ( iii) C contained in steel containers and crushed beads used during grinding, and (iv) C contained in organic PVA (polyvinyl alcohol) which is a binder mixed during granulation. Of these, PVA added to the final step of the production of (iv) is in contact with the outside of the ferrite particles, so most of the PVA is decomposed and burned in the middle of the firing temperature rise and discharged outside the core. A condition for complete combustion at this stage may be used. Although the amount of C contained in the main raw material (i) and C mixed from the pulverizer (iii) is large, most of it is burned in the calcination or firing step and discharged to the outside.

Therefore, for C in the above (i), (iii) and (iv), it was found that the amount of residual C can be reduced if the firing conditions are controlled well, but in the addition of CaO in (ii) above. In general, when added in the form of carbon-containing CaCO ₃ , CaCO ₃ is decomposed and discharged in the firing process, but often remains in the crystal grains or at the grain boundaries. We found that residual C increased. Therefore, it was found that the amount of residual C can be suppressed to 50 massppm or less by adding CaO as an additive as a Ca compound in a form not containing carbon. Specifically, the amount of residual C can be suppressed to 50 massppm or less by adding it in the form of CaO oxide instead of the form of CaCO ₃ carbonate generally used when adding CaO. Become. The Ca compound not containing carbon may be in the form of calcium hydroxide (Ca (OH) ₂ ) or calcium fluoride (CaF ₂ ) in addition to CaO. However, from the viewpoint of cost and the like, addition in the form of CaO is preferable.

  The Mn-Zn-Ni ferrite of the present invention is usually pulverized by mixing the powder raw materials so as to have a predetermined final composition and then mixing additive components with the obtained calcined ferrite powder. Thereafter, it is manufactured by granulating and compression molding, and then firing. In such a normal method, in particular, in the present invention, the oxygen concentration in the firing atmosphere is changed from 5 vol% to 21 vol% (which is the concentration in the atmosphere) until the firing holding temperature is reached from 400 ° C. during the heating process. It is characterized in that it is fired as follows.

From the start of firing to 400 ° C, PVA added to the calcined ferrite powder almost decomposes and burns. Thereafter, it is known that when the oxygen concentration until the firing holding temperature is reduced, crystal grain growth proceeds rapidly, and as a result, high initial permeability is obtained and iron loss is also reduced. However, if the oxygen concentration from 400 ° C. to the firing holding temperature is made too low, this time, as described above, C mixed in each step is not sufficiently burned and decomposed and is taken into the crystal, so the residual C amount is reduced. It does not reduce, but rather hinders the effect of improving the initial permeability and iron loss. As a result of various examinations in view of this, if the oxygen concentration in the firing atmosphere is controlled to 5% by volume or more from 400 ° C. during the temperature rise until the firing holding temperature is reached, the balance between the grain growth and the residual C amount is achieved, It was found that low iron loss on the high temperature side of 150 ° C or higher can be realized.
In addition, since it is a big problem in terms of cost to make the oxygen concentration higher than the concentration in the air, the upper limit is preferably 21% by volume of the atmospheric oxygen concentration.

Fe ₂ O ₃ : 54.5 mol%, ZnO: 6.5 mol%, NiO: 0.17 mol%, and the balance MnO were mixed and calcined at 925 ° C for 3 hours in the atmosphere. To this calcined powder, SiO ₂ , CaO, Nb ₂ O ₅ and BeO were added as 100 massppm, 700 massppm, 200 massppm and 60 massppm respectively, and after grinding for 12 hours with a ball mill, the outer diameter was 31 mm after firing. Molded into a ring shape with an inner diameter of 19 mm and a height of 7 mm, then heated to 400 ° C. at 250 ° C./h in the atmosphere, and various oxygen shown in Table 1 from 400 ° C. to a holding temperature of 1330 ° C. Under the concentration, the temperature was raised at a heating rate of 600 ° C./h. Thereafter, after reaching a holding temperature of 1330 ° C., the oxygen concentration was controlled to 10% by volume or less, and firing was performed for 2 hours.

For the ring-shaped sample thus obtained, an AC BH loop tracer was used to measure the iron loss when excited to a magnetic flux density of 200 mT at a frequency of 100 kHz in a temperature range of 25 ° C. to 180 ° C. The saturation magnetic flux density in a temperature range of 25 ° C. to 180 ° C. was measured using a loop tracer. The saturation magnetic flux density is a value measured as the magnetic flux density when the magnetizing force is 1200 A / m. The amount of residual C was measured by a high-frequency combustion type / infrared absorption method in which a sample was burned in an oxygen stream, the generated CO ₂ gas was detected by an infrared detector, and converted to a carbon amount.

Table 1 shows the amount of residual C and magnetic properties of the obtained sintered body. In Table 1, those within the scope of the present invention are invention examples, and those outside the scope are comparative examples. In addition, although CaO was added in the form of CaO which is an oxide among the additives in the invention examples, it was added in the form of CaCO ₃ which is a carbonate in some of the comparative examples.

As shown in Table 1, according to the invention example, the residual C amount is reduced to 50 massppm or less by controlling the oxygen concentration in the firing atmosphere to 5 vol% or more from 400 ° C. during the temperature rise until the firing holding temperature is reached. At that time, the saturation magnetic flux density at 150 ° C is 380 mT or more, the minimum magnetic loss temperature measured at a maximum magnetic flux density of 200 mT and a frequency of 100 kHz is 150 to 170 ° C, and the iron loss at 160 ° C is 450 kW / m ³ or less is obtained. Therefore, if such a ferrite core is mounted as a transformer core, excellent power supply characteristics can be exhibited in a high temperature range of 150 ° C. or higher.

After mixing the raw materials so as to have various Fe ₂ O ₃ , ZnO and NiO compositions as shown in Tables 2 and 3 and the balance being MnO, calcining in the atmosphere at 930 ° C. for 3 hours As shown in Tables 2 and 3, to this calcined powder, various amounts of SiO ₂ , CaO, Nb ₂ O ₅ and BeO were added as additive components and pulverized with a ball mill for 10 hours. It was molded into a ring shape with an outer diameter of 31 mm, an inner diameter of 19 mm, and a height of 7 mm. Thereafter, the heating rate from 400 ° C. to 1340 ° C. was set to 650 ° C./h and the oxygen concentration was set to 12% by volume. Thereafter, the oxygen concentration was controlled within the range of 1 to 5% by volume at 1340 ° C. X2 hours of baking.

For the ring-shaped sample thus obtained, using an AC BH loop tracer, the iron loss when excited to a magnetic flux density of 200 mT at a frequency of 100 kHz in the temperature range of 25 ° C. to 180 ° C., also using the DC BH loop tracer Then, the saturation magnetic flux density at a magnetizing force of 1200 A / m in a temperature range of 25 ° C. to 180 ° C. was measured. The amount of residual C was measured by a high-frequency combustion type / infrared absorption method in which a sample was burned in an oxygen stream, the generated CO ₂ gas was detected by an infrared detector, and converted to a carbon amount.

Based on the above measurement results, the amount of residual C and magnetic characteristics are shown in Tables 2 and 3 together with the temperature at which the iron loss is minimized and the iron loss value at 150 ° C. In addition, although CaO was added in the form of CaO which is an oxide among the additives in the invention examples, it was added in the form of CaCO ₃ which is a carbonate in some of the comparative examples.
Here, Nos. 2-1 to 34 in Table 2 show examples of the invention according to the present invention, and Nos. 2-35 to 76 in Table 3 show comparative examples of the invention.

As can be seen from Tables 2 and 3, in the present invention, the basic composition of Fe ₂ O ₃ , ZnO, MnO, and NiO and the composition of additive components of SiO ₂ , CaO, Nb ₂ O ₅ , and BeO were appropriately selected. In addition, as a result of controlling the amount of impurity C to 50 massppm or less, the iron loss minimum temperature measured at a maximum magnetic flux density of 200 mT and a frequency of 100 kHz is in the range of 150 to 170 ° C under any condition, and the saturation magnetic flux density at 150 ° C is above 380MT, and has a core loss at 160 ° C. is 450 kW / m ³ or less, or 400 kW / m ³ or less, at a high temperature range above 0.99 ° C., Mn-Zn- high saturation magnetic flux density and low loss Ni-based ferrite material has been obtained.

  The ferrite of the present invention has a high saturation magnetic flux density and a low iron loss in a high temperature range of 150 ° C. or higher, so that it can be used for various power transformer cores for automobiles, choke coils, etc. whose operating temperature is higher than that of normal electronic devices. Can do.

Claims (3)

Fe ₂ O ₃ : 54.0 to 55.0 mol%,
ZnO: 5.0 to 10.0 mol%,
NiO: 0.1 to 0.2 mol% and the balance MnO as basic components,
For the basic component,
SiO ₂ : 50 to 500 massppm,
CaO: 200-2000 massppm,
Nb ₂ O ₅ : 50-500 massppm and
BeO: 10-100 massppm
Is an Mn-Zn-Ni based ferrite consisting of inevitable impurities,
The Mn-Zn-Ni ferrite, wherein the carbon content in the inevitable impurities is suppressed to 50 massppm or less. 0.99 ° C. and saturated magnetic flux density at a magnetizing force 1200A / m or more 380MT, maximum magnetic flux density iron loss minimum temperature at 200mT and frequency 100kHz is 150-170 ° C., and the iron loss at 160 ° C. is 450 kW / m ³ or less The Mn-Zn-Ni ferrite according to claim 1, Oxide raw materials are weighed according to the basic component composition, mixed, calcined, then added with auxiliary components, mixed, further molded after pulverization, and then heated at a firing holding temperature. In the method for manufacturing the Mn-Zn-Ni ferrite according to claim 1 or 2,
CaO as an accessory component is added as a Ca compound that does not contain carbon,
A method for producing an Mn—Zn—Ni-based ferrite, characterized in that an oxygen concentration in an atmosphere from 400 ° C. to a firing holding temperature is set to 5% by volume or more when the temperature is raised.