JP5786322B2 - Ferrite core - Google Patents

Description

  The present invention relates to a ferrite core made of a sintered body containing a main component containing Fe, Mn and Zn and a subcomponent containing Co, Ti, Si and Ca.

  Ferrite sintered bodies are used as magnetic core materials for power transformers and the like. The ferrite sintered body forming the core (magnetic core) is called a ferrite core, and MnZn-based ferrite containing Mn and Zn is widely used. From the viewpoint of reducing the amount of heat generated during use of the device, the ferrite core is required to have a small power loss (core loss) value over a wide temperature range (see Patent Document 1 below).

  In recent years, in order to cope with the downsizing of electronic devices and power supplies, there has been a strong demand for downsizing and thinning of a core that occupies a large part volume. In electronic devices, the density of parts is also increasing. Under such circumstances, the temperature rise due to heat generation tends to increase, and the temperature of the ferrite core tends to increase accordingly. For example, Patent Literature 2 discloses a ferrite sintered body suitable for use under high temperature conditions and a method for manufacturing the same.

JP 2005-119892 A JP 2009-227554 A

  By the way, conventionally, whether or not the magnetic core material is suitable for use under high temperature conditions has been evaluated by measuring the “bottom temperature” of the magnetic core material. This bottom temperature means a temperature at which the power loss has a minimum value. In Patent Documents 1 and 2, the temperature characteristics of the magnetic core material are evaluated from the relationship between the operating temperature and the power loss, and the suitability is evaluated.

  Conventionally, if the operating temperature of electronic devices and power supplies is lower than the bottom temperature, even if the temperature of the core gradually rises during use, the amount of heat generation will gradually decrease, so that the occurrence of thermal runaway can be sufficiently prevented It was thought. However, the present inventors have assumed that the device on which the core is mounted is operated continuously, and when the temperature change of the core is measured by exciting continuously, even when the operating temperature is lower than the bottom temperature. It has been found that the core temperature may continue to rise.

  The present inventors infer that the difference between the evaluation based on the bottom temperature and the result of the core temperature measurement during continuous operation is caused by the bottom temperature measurement method. That is, the bottom temperature is measured by repeatedly measuring the core while measuring the power loss by exciting the core instantaneously or for a very short time (about 5 seconds) after setting the core at a predetermined temperature. Is a value obtained by. In other words, it is presumed that the bottom temperature is not a value measured by continuous excitation.

  A core material with a relatively high bottom temperature and a sufficiently low power loss at the bottom temperature is said to have good initial characteristics (static characteristics) at the start of excitation. Some temperature rises.

  Accordingly, an object of the present invention is to provide a ferrite core that can sufficiently suppress an increase in core temperature and has a sufficiently high saturation magnetic flux density even in an environment in which continuous excitation is performed.

  The present inventors have intensively studied the composition of a ferrite sintered body that can sufficiently suppress an increase in core temperature even when continuously excited and has a sufficiently high saturation magnetic flux density. It was found that a ferrite sintered body within the range is useful as a core.

That is, the ferrite core of the present invention, when converted to the respective oxides, 51.0 to 54.0 mol% of _Fe 2 _O 3, _34.5~40.0 mol% of MnO, and 9.0 Co, Ti, Si, and Ca in the amounts shown in the following (1) to (4) with respect to 1 mass part of the total mass of the main component consisting of ˜11.5 mol% ZnO and the above-mentioned main oxide. When the content ratio of Fe ₂ O ₃ is A mol% and the content ratio of ZnO is B mol%, the value of the ratio A / B is 4.5 to 6.0.
(1) When converted to CoO, an amount of Co equivalent to 1200 × 10 ^{−6 to} 5000 × 10 ⁻⁶ parts by mass,
(2) When converted to TiO ₂ , an amount of Ti equivalent to 1200 × 10 ^{−6 to} 6000 × 10 ⁻⁶ parts by mass,
(3) When converted to SiO ₂ , an amount of Si equivalent to 50 × 10 ^{−6 to} 150 × 10 ⁻⁶ parts by mass,
(4) When converted to CaCO ₃ , an amount of Ca equivalent to 500 × 10 ^{−6 to} 1500 × 10 ⁻⁶ parts by mass.

From the viewpoint of further suppressing temperature rise, the ferrite core has a Mo content of less than 50 × 10 ⁻⁶ parts by mass in terms of MoO _{3 with} respect to 1 part by mass of the total mass of the main component oxide. Is preferred. Moreover, it is preferable that the said ferrite core further contains Nb and / or V of the quantity shown to the following (5), (6) with respect to 1 mass part of total mass of the said oxide whose subcomponent is a main component.
(5) When converted to Nb ₂ O ₅ , an amount of Nb equivalent to 100 × 10 ^{−6 to} 400 × 10 ⁻⁶ parts by mass,
(6) V converted to V ₂ O ₅ is an amount of V equivalent to 50 × 10 ^{−6 to} 400 × 10 ⁻⁶ parts by mass.

  When the ferrite core contains Nb and / or V in the amounts shown in the above (5) and (6) as subcomponents, the grain boundary of the ferrite core becomes high resistance, and the power loss can be further reduced.

  According to the present invention, there is provided a ferrite core that can sufficiently suppress an increase in core temperature and has a sufficiently high saturation magnetic flux density even in an environment in which continuous excitation is performed.

1 is a perspective view showing an embodiment of a ferrite core according to the present invention. It is a graph which shows an example of the temperature setting in a main baking process. Is a graph showing the relationship between the ratio of the content of the ZnO content of the _{Fe 2 O 3 (A / B} ) as the core of the temperature rise ([Delta] T). Fe content and ZnO ratio of the content of the ₂ O ₃ (A / B) and a graph showing the relationship between the saturation magnetic flux density. The ratio of the content of the ZnO content of the Fe ₂ O ₃ and (A / B) is a graph showing the relationship between the power loss at the bottom temperature.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a perspective view showing a ferrite core (magnetic core) according to this embodiment. As shown in FIG. 1, the E-shaped ferrite core 10 is called an E-type core and is used for a transformer or the like. As a transformer in which an E-type core such as the ferrite core 10 is adopted, a transformer in which two E-type cores are arranged to face each other is known.

<Ferrite core>
The ferrite core 10 is made of a ferrite sintered body, and contains a main component including Fe, Mn, and Zn and a subcomponent including Co, Ti, Si, and Ca. The main component of the ferrite core, when converted to the respective oxides, 51.0 to 54.0 mol% of _Fe 2 _O 3, _34.5~40.0 mol% of MnO, and 9.0 to 11. It consists of 5 mol% ZnO. The subcomponent of the ferrite sintered body contains Co, Ti, Si, and Ca in the amounts shown in the following (1) to (4) with respect to 1 part by mass of the total mass of the main oxide.
(1) When converted to CoO, an amount of Co equivalent to 1200 × 10 ^{−6 to} 5000 × 10 ⁻⁶ parts by mass,
(2) When converted to TiO ₂ , an amount of Ti equivalent to 1200 × 10 ^{−6 to} 6000 × 10 ⁻⁶ parts by mass,
(3) When converted to SiO ₂ , an amount of Si equivalent to 50 × 10 ^{−6 to} 150 × 10 ⁻⁶ parts by mass,
(4) When converted to CaCO ₃ , an amount of Ca equivalent to 500 × 10 ^{−6 to} 1500 × 10 ⁻⁶ parts by mass.

The ferrite sintered body forming the ferrite core 10 has a ratio A / B of 4.5 to 6.0, where the Fe ₂ O ₃ content is A mol% and the ZnO content is B mol%. is there. When the value of A / B is less than 4.5, the saturation magnetic flux density becomes low, and when it exceeds 6.0, the temperature rise of the core becomes high. From this viewpoint, the value of A / B is preferably 4.5 to 5.9, and more preferably 4.5 to 5.8. Since the ferrite core 10 has high reliability under high temperature conditions (about 100 to 150 ° C.), the ferrite core 10 can be suitably used for a miniaturized device in which the operating temperature is likely to be high or a device in which components are mounted at a high density. .

  The reason why the ferrite sintered body forming the ferrite core 10 has the above composition is as follows.

(Main component)
When the content of Fe ₂ O _{3 in} the ferrite sintered body is less than 51.0 mol%, the saturation magnetic flux density is lowered. On the other hand, when the content of Fe ₂ O ₃ exceeds 54.0 mol%, the deterioration with time of the performance becomes significant when used under high temperature conditions. The content of Fe ₂ O ₃ is more preferably 51.5 to 53.5 mol%.

  When the ZnO content of the ferrite sintered body is less than 9.0 mol%, the temperature at which the core rises increases. On the other hand, when the ZnO content exceeds 11.5 mol%, the saturation magnetic flux density is lowered. As for the content rate of ZnO, it is more preferable that it is 9.0-11.0 mol%.

The content of MnO in the ferrite sintered body is determined as the balance of the main components when the content of Fe ₂ O ₃ and ZnO, which are other main components, is determined.

(Subcomponent)
In order to more reliably prevent thermal runaway of the device, it is desirable to maintain as low a power loss as possible without causing a significant increase in power loss even when continuously excited and operated for a long period of time. Since Co has a relatively large positive value of the magnetic anisotropy constant K1, the effect of being able to sufficiently suppress the temperature change rate of power loss under high temperature conditions is obtained by including an appropriate amount of Co. .

When the content of Co in the ferrite sintered body (CoO conversion) is less than 1200 × 10 ⁻⁶ parts by mass with ^respect to 1 part by mass of the total mass of the main component oxides, the power loss under high temperature conditions is increased. Become prominent. On the other hand, when the Co content (CoO conversion) exceeds 5000 × 10 ⁻⁶ parts by mass, the rate of change in power loss under high temperature conditions is suppressed, but the reduction in power loss is insufficient. The content of Co (in terms of CoO) is preferably more than 1500 × 10 ⁻⁶ parts by mass and less than 4500 × 10 ⁻⁶ parts by mass, preferably 1800 × 10 ^{−6 to} 4000 × 10 ⁻⁶ parts by mass. Is more preferable.

By including an appropriate amount of Ti in the ferrite sintered body containing Co, there is an effect that deterioration of performance due to use under high-temperature conditions can be suppressed without causing an increase in power loss. When used under high-temperature conditions, the content of Ti in the ferrite sintered body (in terms of TiO ₂ ) is less than 1200 × 10 ⁻⁶ parts by mass relative to 1 part by mass of the total mass of the main component oxides. Deterioration of performance over time becomes remarkable. On the other hand, when the content of Ti (in terms of TiO ₂ ) exceeds 6000 × 10 ⁻⁶ parts by mass, the saturation magnetic flux density decreases. The Ti content (in terms of TiO ₂ ) is preferably more than 1500 × 10 ⁻⁶ parts by mass and less than 5000 × 10 ⁻⁶ parts by mass, and is preferably 1500 × 10 ^{−6 to} 4000 × 10 ⁻⁶ parts by mass. It is more preferable.

Since Si has the effect of enhancing the sinterability of the ferrite sintered body and contributes to the increase in resistance of the grain boundary, the power loss can be reduced by containing an appropriate amount of Si. The high resistance layer in the ferrite sintered body when the Si content (SiO ₂ equivalent) of the ferrite sintered body is less than 50 × 10 ⁻⁶ parts by mass with respect to 1 part by mass of the total mass of the main component oxides. Is insufficiently formed, and power loss is not sufficiently reduced. On the other hand, if the Si content (in terms of SiO ₂ ) exceeds 150 × 10 ⁻⁶ parts by mass, abnormal grain growth is caused, and the reduction in power loss becomes insufficient. The Si content (in terms of SiO ₂ ) is preferably 60 × 10 ^{−6 to} 130 × 10 ⁻⁶ parts by mass.

Ca, like Si described above, has the effect of enhancing the sinterability of the ferrite sintered body and contributes to the increase in the resistance of the grain boundary. Therefore, by containing an appropriate amount of Ca, the power loss can be reduced. Figured. When the Ca content (calculated as CaCO ₃ ) of the ferrite sintered body is less than 500 × 10 ⁻⁶ parts by mass with respect to 1 part by mass of the main component oxide, the high resistance layer in the ferrite sintered body Is insufficiently formed, and power loss is not sufficiently reduced. On the other hand, when the Ca content (CaCO ₃ equivalent) exceeds 1500 × 10 ⁻⁶ parts by mass, abnormal grain growth is caused and the reduction of power loss becomes insufficient. The Ca content (CaCO ₃ equivalent) is preferably 600 × 10 ^{−6 to} 1300 × 10 ⁻⁶ parts by mass.

The ferrite sintered body according to the present embodiment further includes Nb and / or V in the amounts shown in the following (5) and (6) with respect to 1 part by mass of the total mass of the oxides whose main component is the subcomponent. It is preferable.
(5) When converted to Nb ₂ O ₅ , an amount of Nb equivalent to 100 × 10 ^{−6 to} 400 × 10 ⁻⁶ parts by mass,
(6) V converted to V ₂ O ₅ is an amount of V equivalent to 50 × 10 ^{−6 to} 400 × 10 ⁻⁶ parts by mass.

Since Nb contributes to increasing the resistance of the grain boundary of the ferrite sintered body, the power loss can be reduced by adding an appropriate amount of Nb. When the content of Nb (converted to Nb ₂ O ₅ ) of the ferrite sintered body is less than 100 × 10 ⁻⁶ parts by mass with ^respect to 1 part by mass of the total mass of the main component oxide, the resistance of the grain boundary is increased. Tends to be insufficient, and power loss tends to be insufficiently reduced. On the other hand, if the Nb content (in terms of Nb ₂ O ₅ ) exceeds 400 × 10 ⁻⁶ parts by mass, the crystal structure tends to be non-uniform. The Nb content (in terms of Nb ₂ O ₅ ) is preferably 150 × 10 ^{−6 to} 400 × 10 ⁻⁶ parts by mass.

V, like Nb described above, contributes to increasing the resistance of the grain boundaries of the ferrite sintered body, so that the power loss can be reduced by adding an appropriate amount of V. When the content of V (calculated in terms of V ₂ O ₅ ) of the ferrite sintered body is less than 50 × 10 ⁻⁶ parts by mass with ^respect to 1 part by mass of the total mass of the main component oxide, the resistance of the grain boundary is increased. Tends to be insufficient, and power loss tends to be insufficiently reduced. On the other hand, when the V content (V ₂ O ₅ equivalent) exceeds 400 × 10 ⁻⁶ parts by mass, the crystal structure tends to be non-uniform. The V content (in terms of V ₂ O ₅ ) is preferably 50 × 10 ^{−6 to} 300 × 10 ⁻⁶ parts by mass.

When both Nb and V are contained in the ferrite sintered body, the total content of Nb and V may be appropriately adjusted based on the molecular weights of Nb ₂ O ₅ and V ₂ O ₅ .

In the ferrite sintered body according to the present embodiment, it is preferable to set Mo to an amount shown in the following (7) with respect to 1 part by mass of the total mass of the above oxides whose main component is a subcomponent.
(7) Mo equivalent to less than 50 × 10 ⁻⁶ parts by mass when converted to MoO _3.

Since Mo suppresses abnormal grain growth of ferrite, the power loss can be reduced by adding an appropriate amount of Mo. However, when the content of Mo in the ferrite sintered body (MoO ₃ equivalent) is 50 × 10 ⁻⁶ parts by mass or more with ^respect to 1 part by mass of the total mass of the main component oxide, the temperature rise of the core increases. Tend to. The Mo content (MoO ₃ equivalent) is preferably less than 40 × 10 ⁻⁶ parts by mass, and more preferably less than 20 × 10 ⁻⁶ .

The ferrite sintered body according to the present embodiment may further contain components other than those described above. For example, Ta (Ta ₂ O ₅ ), Zr (ZrO ₂ ), and Hf (HfO ₂ ) contribute to increasing the resistance of the grain boundary of the ferrite sintered body in the same manner as Nb and V described above. The power loss can be reduced by the inclusion.

<Ferrite core manufacturing method>
Next, a method for manufacturing the ferrite core 10 will be described.

First, iron oxide α-Fe ₂ O ₃ , manganese oxide Mn ₃ O ₄ and zinc oxide ZnO as main components are prepared, and these oxides are mixed to obtain a mixture. At this time, the content A of Fe ₂ O ₃ is 51.0 to 54.0 mol%, the content B of ZnO is 9.0 to 11.5 mol%, and A / B (molar ratio) The raw materials are mixed so that becomes 4.5 to 6.0, and the remainder is mainly composed of Mn ₃ O ₄ . At this time, you may mix another compound with the said oxide so that the composition ratio of each oxide component in the mixture finally obtained may be converted into the said oxide, and may become in the said range.

  Next, the mixture of the main components is temporarily fired to obtain a temporarily fired product (a calcining step). The calcination is usually performed in the air. The calcination temperature depends on the components constituting the mixture, but is preferably 800 to 1100 ° C. Moreover, although calcining time is dependent on the component which comprises a mixture, it is preferable to set it as 1-3 hours. Thereafter, the obtained calcined product is pulverized by a ball mill or the like to obtain a pulverized powder.

On the other hand, cobalt oxide CoO, titanium oxide TiO ₂ , silicon oxide SiO ₂ , and calcium carbonate CaCO ₃ that are subcomponents are prepared, and a predetermined amount of the subcomponents are mixed to obtain a mixture. When the above-mentioned calcined product of the main component material is pulverized, the above mixture of subcomponent materials is added and mixed. Thereby, the raw material mixed powder for main baking is obtained (mixing process). Here, subcomponents (Nb ₂ O ₅ , V ₂ O ₅ , Ta ₂ O ₅ , ZrO ₂ , HfO _2, etc.) other than the above components may be added as appropriate. In addition, you may use another compound instead of the said compound so that content of each subcomponent in the mixture finally obtained may be in the said range. Further, for example, it may be used CaO instead of _Co 3 _{O 4} or CaCO _3, instead of the CoO.

  Subsequently, the raw material mixed powder obtained as described above and a suitable binder such as polyvinyl alcohol are mixed and molded into the same shape as the ferrite core 10, that is, an E-shape to obtain a molded body.

  Next, the molded body is fired in a heating furnace (main firing step). FIG. 2 is a graph showing an example of temperature setting in the main firing step. As shown in FIG. 2, the main firing step includes a temperature raising step S1 for gradually heating the molded body in the heating furnace, a temperature holding step S2 for keeping the temperature at 1250 to 1350 ° C., and a temperature lowering gradually from the holding temperature. A slow cooling step S3 and a rapid cooling step S4 for rapid cooling after the end of the slow cooling step S3.

  The temperature raising step S1 is a step of raising the temperature in the heating furnace to a holding temperature described later. The heating rate is preferably 10 to 300 ° C./hour.

  When a predetermined temperature (1250 to 1350 ° C.) is reached by the temperature raising step S1, a temperature holding step S2 for maintaining this temperature is performed. When the holding temperature in the temperature holding step S2 is less than 1250 ° C., the grain growth of the ferrite sintered body becomes insufficient and the hysteresis loss increases, so that the reduction in power loss becomes insufficient. On the other hand, if the holding temperature exceeds 1350 ° C., the grain growth of the ferrite sintered body becomes excessive and the eddy current loss increases, so that the reduction of power loss becomes insufficient. By setting the holding temperature to 1250 to 1350 ° C., the hysteresis loss and the eddy current loss are balanced, and the power loss in the high temperature region can be sufficiently reduced.

  The time (holding time) for firing at the above holding temperature is preferably 2 hours 30 minutes or more. When the holding time is less than 2 hours 30 minutes, grain growth is insufficient even when firing is performed at a temperature of 1250 to 1350 ° C., and power loss is likely to be insufficiently reduced. The holding time depends on the raw materials constituting the pulverized powder, but is preferably 3 to 10 hours.

  After completion of the temperature holding step S2, a slow cooling step S3 is performed. The slow cooling rate in the slow cooling step S3 is preferably 150 ° C./hour or less. When the slow cooling rate exceeds 150 ° C./hour, the residual stress in the grains of the ferrite sintered body tends to increase, and this tends to result in insufficient reduction of power loss. In addition, the said slow cooling rate means the average value in a slow cooling zone, and there may be a part where temperature falls at the speed | rate exceeding this.

  When the temperature is lowered from the holding temperature in the slow cooling step S3, the oxygen concentration in the heating furnace is controlled, and an operation for continuously or stepwise decreasing is performed (oxygen concentration adjusting step). By performing such an operation, the oxygen concentration at a temperature of 1200 ° C. is preferably 0.2 to 2.0% by volume and the oxygen concentration at a temperature of 1100 ° C. is preferably 0.020 to 0.60% by volume.

  The temperature at which the slow cooling step S3 is finished and the rapid cooling step S4 is started (slow cooling end temperature) is preferably 950 to 1150 ° C. When the annealing end temperature is higher than 1150 ° C., the formation of grain boundaries in the ferrite sintered body tends to be insufficient, and this tends to result in insufficient reduction of power loss. On the other hand, if the annealing end temperature is lower than 950 ° C., a heterogeneous phase is likely to occur at the grain boundaries of the ferrite sintered body, which tends to result in insufficient reduction of power loss.

  After completion of the slow cooling step S3, a rapid cooling step S4 is performed. Regarding the temperature range at least from the end temperature of the slow cooling until reaching 800 ° C., the rate of temperature decrease is preferably 150 ° C./hour or more. If the rate of temperature decrease in the temperature region is less than 150 ° C./hour, a heterogeneous phase is likely to occur at the grain boundaries of the ferrite sintered body, and this tends to result in insufficient power loss reduction. After completion of the slow cooling step S3, the inside of the heating furnace is preferably a nitrogen atmosphere (oxygen concentration of 0.03% by volume or less) from the viewpoint of preventing the oxidation of ferrite.

  The present invention is not limited to the above embodiment. For example, in the manufacturing method of the ferrite core 10, a mixture of pulverized powder and a binder is molded before the main firing in order to make the ferrite core 10 have a predetermined shape (E shape). After firing, a ferrite core having a predetermined shape may be manufactured by processing.

  In the above embodiment, when the calcined product obtained by calcining the main component raw material is pulverized, the case where the mixed powder for main firing is prepared by adding the subcomponent raw material is exemplified. The mixed powder may be prepared as follows. For example, after calcining a mixture obtained by mixing a main component material and a subcomponent material before calcining, a mixed powder for main firing may be obtained by pulverizing the calcined product. Alternatively, after calcining the mixed powder obtained by mixing the main component raw material and subcomponent raw material before calcining, when the calcined product is pulverized, further subcomponent raw materials are added for the main firing. You may obtain mixed powder.

  Moreover, in the said embodiment, although the E-shaped ferrite core 10 was illustrated, the shape of a ferrite core is not limited to this. The shape of the ferrite core can be determined according to the shape and application of the device in which the ferrite core is built.

(Preparation of samples 1 to 33)
Each component raw material was finally weighed so as to have the composition shown in Tables 1 and 2, and wet mixed using a ball mill. After the raw material mixture was dried, it was calcined at a temperature of about 900 ° C. in the air. The obtained calcined powder was put into a ball mill and wet pulverized for 3 hours until a desired particle size was obtained.

  The pulverized powder thus obtained was dried, granulated by adding 0.8 parts by mass of polyvinyl alcohol to 100 parts by mass of the pulverized powder, and then the resulting mixture was pressure-molded at a pressure of about 150 MPa to obtain a toroidal shape. A molded body and an E-shaped molded body were obtained. The molded body was subjected to main firing under the conditions shown in Table 3 to obtain a toroidal shape and a plurality of E-shaped ferrite cores having dimensions of an outer diameter of 20 mm, an inner diameter of 10 mm, and a height of 5 mm. The upper surfaces of the middle and outer legs of the E-shaped ferrite core were polished to improve surface accuracy.

(Core temperature)
Two E-shaped ferrite cores respectively manufactured from Samples 1 to 33 were arranged to face each other to form a closed magnetic circuit. The initial temperature of the ferrite core was set to 100 ° C., and then the core temperature was measured with a thermocouple when the core temperature was stabilized by continuous excitation under the conditions of a magnetic flux density of 230 mT and a frequency of 100 kHz. Thereby, the rising temperature (ΔT) of the core was measured.

(Power loss)
The power loss of the toroidal ferrite core was measured as follows. That is, the power loss in the temperature range of 25 to 150 ° C. was measured with a BH analyzer manufactured by Iwadori Measurement under the conditions of a magnetic flux density of 200 mT and a frequency of 100 kHz. The temperature (bottom temperature) at which the measured value of the power loss showed a minimum value in the temperature range of 25 to 150 ° C. was obtained. Moreover, the value of power loss at the bottom temperature (minimum value of power loss) was obtained.

(Saturation magnetic flux density)
The saturation magnetic flux density at 150 ° C. of the toroidal ferrite core was measured by applying a magnetic field of 1200 A / m with a BH curve tracer manufactured by Metron Giken.

(Power loss change rate)
Each ferrite core after measuring the power loss was stored in a thermostat set at a temperature of 200 ° C. for 56 hours. Thereafter, the power loss of each ferrite core was measured again by the same method as described above. The measured value of the power loss at the same temperature before and after performing the above storage treatment was substituted into the following formula to calculate the rate of change in power loss at each temperature. The maximum value of the power loss change rate in the temperature range of 25 to 150 ° C. was defined as the power loss change rate.

Tables 1 and 2 and FIGS. 3 to 5 show the measurement results. As shown in FIGS. 3 and 4, the ferrite core according to the example has a sufficiently high saturation magnetic flux density while sufficiently suppressing an increase in core temperature. In addition, as shown in FIG. 5, no special correlation is recognized between the ratio (A / B) of the content ratio of Fe ₂ O _{3 and} the content ratio of ZnO and power loss.

10: Ferrite core (magnetic core).

Claims (5)

When converted to the respective oxides, 51.0 to 54.0 mol% of _Fe 2 _O 3, 34.5 to 40.0 mol% of MnO, and consists of 9.0 to 11.5 mol% of ZnO The main component,
When converted to CoO, 1200 × 10 ^{−6 to} 5000 × 10 ⁻⁶ parts by mass of Co and TiO ₂ are converted to 2300 × 10 ^{−6 to} 6000 × 10 with respect to 1 mass part of the total mass of the oxides of the main component. ^When converted to ^-6 parts by mass of Ti and SiO ₂ , 50 × 10 ^{−6 to} 150 × 10 ⁻⁶ parts by mass of Si and when converted to CaCO ₃ , 500 × 10 ^{−6 to} 1500 × 10 ⁻⁶ parts by mass of Ca A subcomponent containing
Containing
A ferrite core having a ratio A / B of 4.5 to 6.0, where the Fe ₂ O ₃ content is A mol% and the ZnO content is B mol% . When converted to the respective oxides, 51.0 to 54.0 mol% of _Fe 2 _O 3, 34.5 to 40.0 mol% of MnO, and consists of 9.0 to 11.5 mol% of ZnO The main component,
When converted to CoO, 2800 × 10 ^{−6 to} 5000 × 10 ⁻⁶ parts by mass of Co and TiO ₂ are converted to 1200 × 10 ^{−6 to} 6000 × 10 with respect to 1 mass part of the total mass of the oxides of the main component. ^When converted to ^-6 parts by mass of Ti and SiO ₂ , 50 × 10 ^{−6 to} 150 × 10 ⁻⁶ parts by mass of Si and when converted to CaCO ₃ , 500 × 10 ^{−6 to} 1500 × 10 ⁻⁶ parts by mass of Ca A subcomponent containing
Containing
A ferrite core having a ratio A / B of 4.5 to 6.0, where the Fe ₂ O ₃ content is A mol% and the ZnO content is B mol% . The content of Mo is the total mass 1 part by mass of the oxide of the main component is less than 50 × ^{10 -6} parts by weight calculated as MoO _3, ferrite core according to claim 1 or 2. The subcomponent, with respect to the total mass 1 part by mass of the oxide of the main component, further containing Nb of 100 × ^{10 -6} ~400 × ¹⁰ -6 parts by terms of _Nb 2 _{O 5,} claim 1 The ferrite core as described in any one of -3. The subcomponent, with respect to the total mass 1 part by mass of the oxide of the main _component, further includes a V of 50 × ^{10 -6} ~400 × ¹⁰ -6 parts by weight in terms of V 2 _{O 5,} claim 1 The ferrite core according to any one of to 4 .

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