MnZn-BASED SOFT FERRITE AND METHOD FOR PRODUCING SAME

Abstract

[Problem] To provide: a MnZn-based soft ferrite that exhibits a small magnetic core loss in a wide temperature range; and a method for producing the same. [Solution] This MnZn-based soft ferrite is characterized by containing: a main component comprising 54.0-55.5 mol% of Fe expressed as Fe2O3, 3-7 mol% of Zn expressed as ZnO, and Mn as the remaining portion expressed as MnO; and a sub component comprising 0.25-0.7 mass% of Co expressed as Co3O4 in outer percentage with respect to the total of 100 mass% of the main component expressed as said oxides. The MnZn-based soft ferrite is characterized in that the mol ratio of ZnO / Fe2O3 is 0.0541-0.127, the ratio of Co3O4 / Fe2O3 is 0.00450-0.0130, and the ratio of (Co3O4)2 / ZnO is 0.0135-0.112.

Description

MnZn-based soft ferrite and its manufacturing method

[0001] The present invention relates to an MnZn-based soft ferrite suitable for use in electronic components such as transformers, inductors, reactors, and choke coils of various power supply devices, particularly in the magnetic cores of transformers in power supply devices for data servers, and to a method for producing the same.

[0002] Core loss occurs in magnetic core materials such as soft ferrites used in transformers during power conversion. Core loss not only reduces power conversion efficiency, but also converts into heat, acting as a heat source and raising the ambient temperature, potentially damaging the reliability of electronic components.

[0003] In server applications such as industrial network equipment in data centers, there is a strong demand for smaller and lighter size through higher frequencies and higher magnetic flux densities to accommodate increasing data speeds and capacities, while also increasing demand for energy savings. There is also a growing demand for lower semiconductor losses through higher magnetic flux densities. These applications range from general-purpose servers with frequency bands of several hundred kHz to servers with high-frequency bands of several MHz. For example, when using general-purpose MnZn-based soft ferrites in high-frequency bands above 500 kHz, the increased eddy current loss leads to increased core loss (Pcv), which causes equipment overheating and a decrease in efficiency. Therefore, there is a growing demand for soft ferrites with low core loss (Pcv) that can accommodate higher frequencies.

[0004] WO 2017 / 164351 (Patent Document 1) describes a magnet used at a frequency of 1 MHz or more and an excitation magnetic flux density of 75 mT or less, which contains 53 to 56 mol% Fe as calculated as Fe2O3, 3 to 9 mol% Zn as calculated as ZnO, and the remainder Mn as calculated as MnO as main components, and contains, in outer percentages relative to 100 mass% of the total of the main components as calculated as oxides, 0.05 to 0.4 mass% Co as calculated as Co3O4, 0.003 to 0.015 mass% Si as calculated as SiO2, 0.06 to 0.3 mass% Ca as calculated as CaCO3, 0 to 0.1 mass% V as calculated as V2O5, 0.05 mass% or less (excluding 0) Nb as calculated as Nb2O5, and 0 to 0.1 mass% Ta as calculated as Ta2O5 as auxiliary components, and the core loss Pcv is 200 mT or less at a frequency of 2 MHz and an excitation magnetic flux density of 50 mT or less. 1100 kW / m between 0 and 120°C at mT 3 This MnZn-based ferrite core is obtained by a method including a heat treatment step in which, after sintering, the core is heated to a temperature that is 200°C or higher and satisfies the conditions of (Tc - 90)°C to (Tc + 100)°C (where Tc is the Curie temperature (°C) determined from the mole percentages of Fe2O3 and ZnO contained in the main components of the MnZn-based ferrite), held for a certain period of time, and then cooled at a cooling rate of 50°C / hr or less.

[0005] However, although the MnZn ferrite described in Patent Document 1 is found to have a significant reduction in core loss due to the heat treatment process, there is a demand for a further reduction in core loss in the high frequency band.

[0006] JP 2009-227554 A (Patent Document 2) discloses a composite material containing 52 to 54 mol% of Fe2O3, 35 to 42 mol% of MnO, and 6 to 11 mol% of ZnO as main components, calculated as oxides, and 1000×10 CoO equivalents per 1% by mass of the total mass of the oxides of the main components. -6 ~3500×10 -6 Mass% Co, TiO2 equivalent: 2000 x 10 -6 ~5000×10 -6 Mass% Ti, SiO2 equivalent: 50 x 10 -6 ~150×10 -6 % by mass of Si and 300 x 10 CaCO3 equivalent -6~1500×10 -6 % by mass of Ca, and in a magnetic field with an excitation magnetic flux density of 200 mT and a frequency of 100 kHz, the temperature at which the power loss shows a minimum value is higher than 120°C, and the power loss at the temperature at which the power loss shows a minimum value is 350 kW / m 3 Patent Document 2 discloses a ferrite sintered body characterized by the following: Patent Document 2 states that a magnetic core made of this ferrite sintered body can sufficiently reduce the amount of heat generated even under high-temperature conditions of about 100°C or higher, and can also sufficiently prevent the occurrence of thermal runaway. However, the ferrite sintered body described in Patent Document 2 has a problem in that it has large core loss in the high-frequency band.

[0007] WO 2016 / 032001 (Patent Document 3) discloses a ceramic sintered body containing Fe, Mn, and Zn as main components and Si, Ca, Co, and Bi, at least one of Ta and Nb, and at least one of Ti and Sn as subcomponents, where the total amount of the main components is 100 mol % when the main components are respectively composed of Fe2O3, ZnO, and MnO, and Fe is 53.25 to 54.00 mol % in terms of Fe2O3, Zn is 2.50 to 8.50 mol % in terms of ZnO, and Mn is the remainder in terms of MnO, Si is more than 0.001 mass % and less than 0.02 mass % in terms of SiO2, and Ca is 0.001 mass % and less than 0.02 mass % in terms of CaCO3. It contains more than 0.04% by mass and less than 0.4% by mass, Co less than 0.5% by mass (excluding 0) calculated as Co3O4, Bi less than 0.05% by mass (excluding 0) calculated as Bi2O3, Ta less than 0.05% by mass (including 0) calculated as Ta2O5, Nb less than 0.05% by mass (including 0) calculated as Nb2O5, Ti less than 0.3% by mass (including 0) calculated as TiO2, and Sn less than 0.3% by mass (including 0) calculated as SnO2, with the total amount of Ta2O5 and Nb2O5 being less than 0.05% by mass (excluding 0), and the total amount of TiO2 and SnO2 being less than 0.3% by mass (excluding 0). The core loss (Pcv130A) at 130°C at a frequency of 100 kHz and a maximum magnetic flux density of 200 mT is 400 kW / m 3The document discloses an MnZn-based ferrite characterized in that the rate of change in core loss Ps, calculated from the Pcv130A and the core loss at 130°C after holding at 200°C for 96 hours (Pcv130B), is 5% or less, using the formula Ps (%) = [(Pcv130B - Pcv130A) / Pcv130A] × 100. This MnZn-based ferrite has suppressed changes in magnetic properties over time in high-temperature environments, and can suppress increases in core loss, but further reductions in core loss in the high-frequency band are required.

[0008] Japanese Patent Laid-Open Publication No. 2007-70209 (Patent Document 4) discloses a method for producing MnZn-based ferrite containing 51.5 to 57.0 mol% FeO, 0 to 15 mol% ZnO, and the remainder substantially MnO as the base component, and 0 to 5,000 ppm Co oxide (calculated as CoO). The method includes a sintering process including a high-temperature holding step and a temperature-reducing step. In the temperature-reducing step, the atmosphere switching temperature α1 (°C) for switching from an oxygen partial pressure-controlled atmosphere to a nitrogen atmosphere satisfies the condition 900≦α1≦1,175, and the cooling rate α2 (°C / hrs) after switching to the nitrogen atmosphere satisfies the relationship 3.8≦α1 / α2≦200. Patent Document 4 states that it is possible to provide an MnZn-based ferrite with low core loss over a wide temperature range. However, the MnZn-based ferrite disclosed in Patent Document 4 suffers from a problem of poor core loss in the high-frequency range.

[0009] International Publication No. 2017 / 164351, Japanese Patent Application Laid-Open No. 2009-227554, International Publication No. 2016 / 032001, Japanese Patent Application Laid-Open No. 2007-70209

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an MnZn-based soft ferrite having small core loss in the high frequency band, and a method for producing the same.

[0011] When a soft ferrite material designed for use at frequencies below 1 MHz is used at, for example, 2 MHz, the residual loss Pr, which is thought to be caused by domain wall motion, increases. However, it was found that effective ways to reduce the residual loss Pr are (a) increasing the resonant frequency of the domain wall, (b) imparting induced magnetic anisotropy Ku, and (c) enhancing the effect of imparting induced magnetic anisotropy Ku.

[0012] Regarding (a), as the saturation magnetic flux density Bs increases, the domain wall resonance frequency fr (∝Bs / Ku 1 / 2 / μi 1 / 2 ) also becomes higher, and as a result, the domain wall motion becomes more likely to follow the magnetic field change. Therefore, it is necessary to select a composition with a high saturation magnetic flux density Bs. It was found that in order to obtain a composition with a high Bs, it is necessary to reduce the Zn content. Regarding (b), when heat treatment is performed after firing, the Co 2+ It was found that the magnetic domains are rearranged, stabilizing their orientation and imparting induced magnetic anisotropy Ku. The impartation of induced magnetic anisotropy Ku increases the resonant frequency of the domain walls. Furthermore, the same effect as heat treatment can be obtained by slow cooling during the cooling process of the temperature-lowering part during sintering without heat treatment. Regarding (c), when the amount of Co3O4 added is increased, the Co 2+ It was found that the effect of imparting induced magnetic anisotropy is promoted by increasing the oxygen concentration in the temperature-reducing section (holding temperature ~ 900°C) during the sintering process. 2+ It was found that this facilitates rearrangement, increases the stabilization of the magnetic domain direction, promotes the effect of imparting induced magnetic anisotropy Ku, and increases the resonant frequency of the domain walls. In this way, (c) enhances the effect of the post-sintering heat treatment described above in (b).

[0013] Of the three above, the effects of (a) and (c) were particularly pronounced, and as a result of extensive research into the composition of MnZn-based soft ferrite, it was discovered that simply reducing the Zn content and increasing the amount of Co3O4 added was not enough to sufficiently reduce the residual loss Pr in the high frequency band (for example, 1 to 2 MHz). Therefore, the relationship between the amount of Zn and Co and the main component Fe, and the relationship between the amount of Co and the amount of Zn were also examined, and it was found that by increasing or decreasing the amount of Co and Zn to a predetermined value, and by adjusting the molar ratio of ZnO / Fe2O3, the ratio of Co3O4 / Fe2O3, and the (Co3O4) 2 The present inventors have found that when the ratio of MnZnO to ZnO is kept within a predetermined range, the residual loss Pr of MnZn-based soft ferrite in the high frequency band is significantly reduced, leading to the present invention.

[0014] Furthermore, when soft ferrite designed for low excitation magnetic flux density is used at high excitation magnetic flux density, the hysteresis loss Ph caused by magnetic hysteresis and the eddy current loss Pe caused by Joule heat due to current generated in the soft ferrite as magnetization changes increase.To reduce the hysteresis loss Ph and eddy current loss Pe, we thought that (a) decreasing the magnetocrystalline anisotropy constant K1, (b) increasing the resistivity of the grain boundary, and (c) increasing the crystal grain size would be effective.

[0015] Specifically, for (a), the amount of Co3O4 added was adjusted. 2+ By adjusting the amount of Co3O4 added so that the amount is (a), the initial permeability μi increases. As a result, the area of ​​the hysteresis loop decreases and Ph decreases. To achieve (b), the amounts of CaCO3, SiO2, and Nb2O5 added were adjusted. To achieve (c), the high-temperature holding temperature in the sintering process was increased. When the crystal grain size increases as the high-temperature holding temperature increases, μi increases, the area of ​​the hysteresis loop decreases, and Ph decreases, but if the high-temperature holding temperature is raised too much, coarse grains are generated and Ph increases instead.

[0016] That is, the MnZn-based soft ferrite of the present invention contains a main component consisting of 54.0 to 55.5 mol% Fe as calculated as Fe2O3, 3 to 7 mol% Zn as calculated as ZnO, and the remainder Mn as calculated as MnO, and a subcomponent containing 0.25 to 0.7 mol% Co as calculated as Co3O4 in outer percentage relative to 100 mol% of the total of the main components as calculated as oxides, and the ratio of the Zn content (mol% as calculated as ZnO) to the Fe content (mol% as calculated as Fe2O3) in the main component (ZnO / Fe2O 3) is 0.0541 to 0.127, the ratio (Co3O4 / Fe2O3 ratio) of the Co content (mass % in terms of Co3O4 relative to 100 mass % of the total of the main components) to the Fe content in the main component (mol % in terms of Fe2O3) is 0.00450 to 0.0130, and the ratio [(Co3O4) 2 / ZnO ratio] is 0.0135 to 0.112.

[0017] The MnZn-based soft ferrite of the present invention has a sintered density of 4.65 g / cm 3 More preferably, it is equal to or greater than this.

[0018] The MnZn-based soft ferrite of the present invention preferably has an average crystal grain size of 2 to 5 μm.

[0019] The MnZn-based soft ferrite of the present invention has a maximum core loss value Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. max is 3800 kW / m 3 Preferably, it is:

[0020] The MnZn-based soft ferrite of the present invention has a maximum core loss value Pcv at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT at 20 to 100°C. max is 3800 kW / m 3 Preferably, it is:

[0021] The MnZn-based soft ferrite of the present invention preferably has an initial permeability μi of 400 or more.

[0022] A first method for producing an MnZn-based soft ferrite of the present invention comprises the steps of: forming a raw material powder to obtain a green body; sintering the green body; and heat-treating the obtained sintered body; the sintering step comprises a high-temperature holding step of holding the green body for 1 to 12 hours in an atmosphere having an oxygen concentration of more than 0.05% by volume and not more than 10% by volume at a temperature of more than 1055°C and not more than 1205°C; and the heat-treatment step comprises holding the green body for 1 hour or more at a temperature that satisfies the condition of (Tc-100°C) to (Tc-10°C) (where Tc is the Curie temperature measured by the method described in JIS C2560-2), and then cooling it from the holding temperature at a cooling rate of 100 to 200°C / hr or at a cooling rate of 50°C / hr or less.

[0023] A second method of producing MnZn-based soft ferrite of the present invention includes a step of forming a raw material powder to obtain a molded body, and a step of sintering the molded body, wherein the sintering step includes a high-temperature holding step of holding the molded body for 1 to 12 hours in an atmosphere having an oxygen concentration of more than 0.05% by volume and not more than 10% by volume at a temperature of more than 1055°C and not more than 1205°C, and wherein no heat treatment is performed after the sintering step.

[0024] The MnZn-based soft ferrite of the present invention having the above composition has small core loss in the range of 20 to 100°C at an operating frequency of several hundred kHz to several MHz, for example, 0.5 to 2 MHz, and at an excitation magnetic flux density of several tens of mT or more, for example, 75 mT or more. Therefore, when used in the magnetic core of a power supply device for a data server, for example, it can contribute to improving power supply efficiency and saving energy.

[0025] 1 is a graph showing the temperature conditions of a typical sintering process for obtaining the MnZn-based soft ferrite of the present invention, 2 is a graph showing the use conditions of the MnZn-based soft ferrite of the present invention, and 3 is a graph showing the use conditions of the MnZn-based soft ferrite of the present invention.

[0026] Although the embodiments of the present invention will be described in detail below, the present invention is not limited thereto and can be modified as appropriate within the scope of the technical concept of the present invention.

[0027] [1] MnZn-based soft ferrite (A) Composition The MnZn-based soft ferrite of the present invention contains a main component consisting of Fe, Mn, and Zn, and a subcomponent containing Co. The subcomponent preferably further contains Ca and Si. The MnZn-based soft ferrite of the present invention may further contain Nb as a subcomponent. The main component is an element that mainly constitutes spinel ferrite, and the subcomponent is an element that assists in the formation of spinel ferrite. Co is also an element that constitutes spinel ferrite, but since its content is significantly lower than that of the main component, it is considered a subcomponent in the present invention.

[0028] (1) Main Components (a) Fe: 54.0 to 55.5 mol% (Fe2O3 equivalent). If the Fe content, calculated as Fe2O3, is less than 54.0 mol% or more than 55.5 mol%, assuming the total of the main components to be 100 mol%, the effect of reducing core loss in the high frequency band is insufficient. The lower limit of the Fe content is preferably 54.3 mol%, more preferably 54.5 mol%. Meanwhile, the upper limit of the Fe content is preferably 54.9 mol%, more preferably 54.8 mol%. An example of the range of the Fe content is preferably 54.3 to 54.9 mol%, more preferably 54.5 to 54.8 mol%. However, the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, such as 54.3 to 55.5 mol%. Therefore, the present specification also describes the optimal combination of any of the general upper limit, preferred upper limit, and more preferred upper limit with any of the general lower limit, preferred lower limit, and more preferred lower limit.

[0029] (b) Zn: 3 to 7 mol% (ZnO equivalent). By reducing the Zn content to a relatively low level of 3 to 7 mol%, assuming the total of the main components to be 100 mol%, the saturation magnetic flux density Bs of the MnZn-based soft ferrite increases, enhancing the effect of reducing core loss in the high frequency band. The lower limit of the Zn content is preferably 3.5 mol%, more preferably 4.0 mol%. Meanwhile, the upper limit of the Zn content is preferably 6.0 mol%, more preferably 5.0 mol%. An example of the Zn content range is preferably 3.5 to 6.0 mol%, more preferably 4.0 to 5.0 mol%, but the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, such as 3.5 to 7 mol%. Therefore, the present specification also describes the optimal combination of any of the general upper limit, preferred upper limit, and more preferred upper limit with any of the general lower limit, preferred lower limit, and more preferred lower limit.

[0030] (c) Mn: balance (calculated as MnO) The Mn content is the balance obtained by subtracting the Fe content and the Zn content from 100 mol % of the total of the main components (Fe, Zn, and Mn).

[0031] (2) Minor components The MnZn-based soft ferrite of the present invention contains Co, Ca, and Si as minor components, and optionally Nb. Co is likely to dissolve in the crystal grains, while Ca, Si, and Nb are likely to segregate at the grain boundaries. The composition of the minor components is expressed in mass% relative to 100% by mass of the total of the main components in terms of the oxides.

[0032] (a) Co: 0.25 to 0.7 mass% (Co3O4 equivalent). Co dissolves easily within crystal grains, reducing residual loss Pr. Too little Co content increases core loss at room temperature. The total of the main components is 100 mass%, and the Co content is 0.25 to 0.7 mass% in terms of Co3O4, calculated as outer percent. The lower limit of the Co content is preferably 0.37 mass%, more preferably 0.4 mass%. The upper limit of the Co content is preferably 0.50 mass%, more preferably 0.45 mass%. An example of the Co content range is preferably 0.37 to 0.50 mass%, more preferably 0.4 to 0.45 mass%, but the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, such as 0.37 to 0.7 mass%. Therefore, the present specification also describes an optimal combination of any of the general upper limit, preferred upper limit, and more preferred upper limit with any of the general lower limit, preferred lower limit, and more preferred lower limit.

[0033] (b) Ca: 0.02 to 0.30 mass% (CaCO3 equivalent) Calcium segregates at the grain boundaries and insulates the grains (increasing grain boundary resistance), reducing the relative loss factor tanδ / μ and eddy current loss. As a result, core loss in the high frequency range of MnZn-based soft ferrite is reduced. If the Ca content is too low, the effect of increasing grain boundary resistance is small, while if the Ca content is too high, it actually induces crystal thickening and deteriorates core loss.

[0034] A Ca content of 0.02 to 0.30 mass% (calculated as CaCO3) is preferred, based on 100 mass% of the total main components, because it ensures sufficient grain boundary resistance to reduce eddy current loss and achieves low loss in the high-frequency range. The lower limit of the Ca content is more preferably 0.07 mass%, and most preferably 0.1%. The upper limit of the Ca content is more preferably 0.20 mass%, and most preferably 0.18 mass%. An example of the Ca content range is more preferably 0.07 to 0.20 mass%, and most preferably 0.1 to 0.18 mass%, although the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, such as 0.07 to 0.30 mass%. Therefore, the present specification also describes optimal combinations of any of the general upper limit, preferred upper limit, and more preferred upper limit with any of the general lower limit, preferred lower limit, and more preferred lower limit.

[0035] (c) Si: 0.002 to 0.025 mass% (SiO2 equivalent) Si segregates at grain boundaries, insulating the grains (increasing grain boundary resistance), reducing the relative loss coefficient tanδ / μ and eddy current loss. As a result, core loss in the high frequency range of MnZn soft ferrite is reduced. If the Si content is too low, the effect of increasing grain boundary resistance is small, while if the Si content is too high, it actually induces crystal thickening and deteriorates core loss.

[0036] A Si content of 0.002 to 0.025 mass% (SiO2 equivalent) based on 100 mass% of the total main components is preferable because it ensures sufficient grain boundary resistance to reduce eddy current loss and enables the MnZn-based soft ferrite to achieve low loss in the high-frequency range. The lower limit of the Si content is more preferably 0.004 mass%, and most preferably 0.005 mass%. The upper limit of the Si content is more preferably 0.013 mass%, and most preferably 0.01 mass%. An example of the Si content range is more preferably 0.004 to 0.013 mass%, and most preferably 0.005 to 0.01 mass%. However, the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, such as 0.004 to 0.025 mass%. Therefore, the present specification also describes optimal combinations of any of the general upper limit, preferred upper limit, and more preferred upper limit with any of the general lower limit, preferred lower limit, and more preferred lower limit.

[0037] (d) Nb: 0 to 0.12 mass% (Nb2O5 equivalent). Nb, along with Si and Ca, segregates primarily in the grain boundary layers, increasing grain boundary resistance and contributing to loss reduction. Therefore, up to 0.12 mass% of Nb, calculated as an outer percentage of 100 mass% of the total main components, may be added in Nb2O5 equivalent. An Nb content exceeding 0.12 mass% induces crystal thickening and reduces core loss. The upper limit of the Nb content is more preferably 0.06 mass%, and most preferably 0.05 mass%. The lower limit of the Nb content may be 0 mass% (none), but 0.01 mass% and most preferably 0.02 mass% are preferred, calculated as Nb2O5. An example of the range of the Nb content is more preferably 0.01 to 0.06 mass%, and most preferably 0.02 to 0.05 mass%, but the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, for example, 0.01 to 0.12 mass%. Therefore, the optimum combination of any of the above general upper limit, preferred upper limit, and more preferred upper limit and any of the above general lower limit, preferred lower limit, and more preferred lower limit is also described in this specification.

[0038] (3) Component Ratios (a) ZnO / Fe2O3 Molar Ratio The molar ratio of the Zn content (mol % calculated as ZnO) to the Fe content (mol % calculated as Fe2O3) in the main components is 0.0541 to 0.127. By increasing the Zn content and maintaining the ZnO / Fe2O3 molar ratio within the above range, the core loss of the MnZn-based soft ferrite can be reduced over a wide temperature range (particularly 20 to 100°C). If the ZnO / Fe2O3 molar ratio is less than 0.0541, the core loss changes rapidly with temperature. On the other hand, if the ZnO / Fe2O3 molar ratio exceeds 0.127, the core loss changes slowly but is high. The upper limit of the ZnO / Fe2O3 molar ratio is preferably 0.1, and more preferably 0.09. The lower limit of the ZnO / Fe2O3 molar ratio is preferably 0.06, and more preferably 0.07. An example of the range of the ZnO / Fe2O3 molar ratio is preferably 0.06 to 0.1, and more preferably 0.07 to 0.09, but the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, such as 0.06 to 0.127. Therefore, the optimal combination of any of the general upper limit, preferred upper limit, and more preferred upper limit, and any of the general lower limit, preferred lower limit, and more preferred lower limit, is also described in this specification.

[0039] (b) Co3O4 / Fe2O3 Ratio The ratio of the Co content in the minor components (mass % in terms of Co3O4 relative to 100 mass % of the total of the major components) to the Fe content in the major components (mol % in terms of Fe2O3) is 0.00450 to 0.0130. If the Co3O4 / Fe2O3 ratio is less than 0.00450 or exceeds 0.0130, the core loss at 20°C or less increases. The upper limit of the Co3O4 / Fe2O3 ratio is preferably 0.009, more preferably 0.008. The lower limit of the Co3O4 / Fe2O3 ratio is preferably 0.006, more preferably 0.007. An example of the range of the Co3O4 / Fe2O3 ratio is preferably 0.006 to 0.009, more preferably 0.007 to 0.008, but the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, for example, 0.006 to 0.0130. Therefore, the optimal combination of any of the above general upper limit, preferred upper limit, and more preferred upper limit with any of the above general lower limit, preferred lower limit, and more preferred lower limit is also described in this specification.

[0040] (c) (Co3O4) 2 / ZnO ratio The ratio of the square of the Co content in the secondary component (mass % in Co3O4 equivalent relative to 100 mass % of the total of the primary component) to the Zn content in the primary component (mol % in ZnO equivalent) is 0.0135 to 0.112. (Co3O4) 2 If the ratio of Co3O4 to ZnO is less than 0.0135 or exceeds 0.112, the core loss at temperatures below 20°C will increase. 2 The upper limit of the ratio of (Co3O4) / ZnO is preferably 0.04, and more preferably 0.038. 2 The lower limit of the ratio of Co3O4 to ZnO is preferably 0.032, and more preferably 0.034. 2An example of the range of the ratio of ZnO to ZnO is preferably 0.032 to 0.04, more preferably 0.034 to 0.038, but the upper limit (or lower limit) may remain the upper limit (or lower limit) of the general range, for example, 0.032 to 0.112. Therefore, the optimum combination of any of the general upper limit, preferred upper limit, and more preferred upper limit and any of the general lower limit, preferred lower limit, and more preferred lower limit is also described in this specification.

[0041] (b) Impurities: The raw materials for MnZn-based soft ferrite may contain impurities such as sulfur (S), chlorine (Cl), phosphorus (P), and boron (B). S, in particular, forms compounds with calcium, which segregate as foreign matter at grain boundaries, reducing volume resistivity (ρ) and increasing eddy current loss. It is empirically known that reducing the content of these impurities reduces core loss and improves magnetic permeability. Therefore, to further reduce core loss, it is preferable to limit S to 0.03 mass% or less, Cl to 0.01 mass% or less, P to 0.001 mass% or less, and B to 0.0001 mass% or less, based on 100 mass% of the total main components in oxide terms. Furthermore, because the addition of Bi can cause deterioration of the sintering furnace, the Bi content should be less than 0.01 mass% in terms of Bi2O5, preferably 0.001 mass% or less, and even more preferably zero.

[0042] The main components, minor components, and impurities can be quantified using X-ray fluorescence analysis and ICP atomic emission spectrometry. Qualitative analysis of the contained elements is first performed using X-ray fluorescence analysis, and then the contained elements are quantified using a calibration curve method that compares them with standard samples.

[0043] (B) Properties (1) Density of sintered body The sintered body of MnZn-based soft ferrite is 4.65 g / cm 3 It is preferable that the sintered body has a density of 4.65 g / cm or more. 3 If the density is less than 4.7 g / cm, the mechanical strength is poor and chipping or cracking may occur. 3 and more preferably 4.75 g / cm 3 The density of the sintered body can be determined by the method described in the following examples.

[0044] (2) Resistivity ρ In order to reduce eddy current loss Pe, the resistivity ρ of the MnZn-based soft ferrite of the present invention at room temperature is preferably 2 Ω·m or more, and more preferably 3 Ω·m or more.

[0045] (3) Initial permeability μi When the magnetic field strength approaches 0, the following formula (1): (where μa represents amplitude permeability, and H represents magnetic field strength) is called initial permeability μi. The initial permeability μi of the MnZn-based soft ferrite of the present invention at 100 kHz and 0.4 A / m is preferably 400 or more, and more preferably 450 or more.

[0046] (4) Relative Loss Factor tan δ / μ The relative loss factor tan δ / μ of the MnZn-based soft ferrite of the present invention is preferably 2.5 or less, and more preferably 2 or less.

[0047] (5) Core Loss Pcv The MnZn-based soft ferrite of the present invention has a maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. max is 3800 kW / m 3 Preferably, it is less than 2000 kW / m 3 More preferably, it is less than 1500 kW / m 3 It is most preferable that the maximum core loss Pcv at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT is max is 3800 kW / m 3 Preferably, it is less than 2000 kW / m 3 It is more preferable that the frequency and excitation magnetic flux density are not more than 1000 kJ / s. Note that the above frequencies and excitation magnetic flux densities are merely examples, and the MnZn-based soft ferrite of the present invention is not limited to use at these frequencies and excitation magnetic flux densities. max = 3800 kW / m 3 Figure 3 shows an example of the relationship between the excitation magnetic flux density Bm and frequency f under the operating conditions of Pcv max = 1000 kW / m 3As shown in Figures 2 and 3, the relationship between the excitation magnetic flux density Bm and frequency f under the following operating conditions is max The combination of frequency f and excitation magnetic flux density Bm can be selected according to the design value of Pcv. Even at frequencies lower than 1 MHz and excitation magnetic flux densities higher than 100 mT, the desired Pcv can be obtained. max value can be obtained.

[0048] [2] Manufacturing Method of MnZn-Based Soft Ferrite Figure 1 shows an example of the temperature conditions for the sintering process to obtain the MnZn-based soft ferrite of the present invention. The sintering process includes a temperature increase step, a high-temperature holding step, and a temperature decrease step, and a heat treatment step is carried out as needed after the sintering process. By adjusting the oxygen partial pressure in the sintering process, Ca, Si, Nb, etc. are segregated to the grain boundaries, and the solid solution of Co within the crystal grains is controlled, thereby reducing core loss. Note that the heat treatment step may not be carried out if core loss at high excitation magnetic flux densities (e.g., 100 mT or higher) is to be reduced.

[0049] (A) Temperature-Raising Step The average temperature-raising rate in the step of raising the temperature from room temperature to the holding temperature is preferably within the range of 50 to 200° C. / hr.

[0050] (B) High-Temperature Holding Step The high-temperature holding step is preferably carried out at a temperature of 1055 to 1205°C. The oxygen concentration in the atmosphere during the high-temperature holding step is preferably adjusted to 0.05 to 10% by volume. The high-temperature holding step is generally carried out for 1 to 12 hours.

[0051] (C) Temperature-reducing step If the oxygen concentration is too high in the temperature-reducing step, oxidation of the sintered body progresses, and hematite precipitates from the spinel. On the other hand, if the oxygen concentration is too low, wüstite precipitates, causing crystal distortion and increasing core loss. It is preferable to control the oxygen concentration in the temperature-reducing step so that the precipitation of hematite and wüstite does not occur. Specifically, the oxygen concentration P O2 (volume fraction) and temperature T (°C) are expressed by the following equation (2): log P O2It is preferable to control the oxygen concentration in the temperature-lowering step so as to satisfy the following equation: = a - b / (T + 273) ... (2) (where a is a constant between 3.1 and 12.8, and b is a constant between 6,000 and 20,000). a is determined by the temperature and oxygen concentration in the high-temperature holding step. If b is less than 6,000, the oxygen concentration will be high even when the temperature is lowered, and oxidation will proceed, which may result in hematite precipitating from the spinel. On the other hand, if b is greater than 20,000, the oxygen concentration will decrease, causing wüstite to precipitate, and both the crystal grains and the grain boundary layers will not be sufficiently oxidized, resulting in low resistance. a is more preferably 6.4 to 11.5, and b is more preferably 10,000 to 18,000.

[0052] In the temperature-reducing step, the cooling rate is preferably 100°C / hr from the holding temperature to 900°C, and 150°C / hr below 900°C. In the temperature-reducing step, the oxygen concentration at 1050°C is preferably 0.1 to 1.0% by volume. In the temperature-reducing step, the oxygen concentration (volume %) is preferably adjusted to an equilibrium oxygen partial pressure up to 900°C. After 900°C, it is preferable to cool in a flowing N2 atmosphere and reduce the final oxygen concentration to approximately 0.002% by volume.

[0053] By combining the appropriate main component composition, subcomponent composition and manufacturing method, the maximum core loss Pcv at 20 to 100°C is the lowest for each composition. max For example, the Fe content (Fe2O3 equivalent) is 54.7 to 54.8 mol%, the Zn content (ZnO equivalent) is 4.3 to 4.4 mol%, the Co content (Co3O4 equivalent) is 0.4 to 0.45 mass%, the Ca content (CaCO3 equivalent) is 0.02 to 0.04 mass%, the Si content (SiO2 equivalent) is 0.05 to 0.01 mass%, the ZnO / Fe2O3 molar ratio is 0.08 to 0.09, the Co3O4 / Fe2O3 ratio is 0.073 to 0.074, and (Co3O4) 2When an MnZn-based soft ferrite having a composition with a ZnO / ZnO ratio of 0.036 to 0.038 is manufactured under the conditions that the temperature in the high-temperature holding step of the sintering process is 1175°C, the oxygen concentration in the atmosphere in the high-temperature holding step is 2% by volume, and the oxygen concentration PO2 in the temperature-lowering step is expressed by the formula logPo2 = a - b / (T + 273) (where T is temperature (°C), a = 9 to 10, and b = 13120 to 13130), and the oxygen concentration at 1050°C is 0.3% by volume, as in Example 55, the maximum core loss Pcv max 2000kW / m 3 The maximum core loss Pcv between 20 and 100°C at 1 MHz and 100 mT can be reduced to a low value of max to 1900kW / m 3 It is more preferable that the maximum core loss Pcv at 1 MHz and 100 mT between 20 and 100°C is max to 1800kW / m 3 It can be reduced to the following:

[0054] (D) Heat Treatment Step: When the excitation magnetic flux density is set to 100 mT or less, particularly 75 mT or less, core loss can be reduced by heat treating the resulting MnZn-based soft ferrite sintered body at a temperature of (Tc - 100°C) to (Tc - 10°C) for at least one hour. Cooling after heat treatment is preferably performed at a rate of 100 to 200°C / hr or at a rate of 50°C / hr or less, where Tc is the Curie temperature measured using the method described in JIS C 2560-2. When the excitation magnetic flux density Bm is low, for example, 100 mT or less, heat treatment reduces core loss. On the other hand, when the excitation magnetic flux density Bm is high, for example, 100 mT or more, heat treatment does not reduce core loss, so heat treatment is not necessarily required.

[0055] The present invention will be described in more detail by the following examples, but the present invention is not limited thereto.

[0056] Examples 1 to 40 and Comparative Examples 1 and 2: Fe2O3 powder, ZnO powder, and Mn3O4 powder were wet-mixed as the main components in the ratios shown in Table 1, then dried and calcined at 860°C for 1.5 hours. The amount of Mn3O4 powder added in Table 1 is shown in terms of MnO. Co3O4 powder, CaCO3 powder, SiO2 powder, and Nb2O5 powder were added to 100% by mass of each calcined powder in a ball mill in the ratios shown in Table 1, followed by pulverization and mixing. The average pulverized particle size of each resulting mixture was measured using the ventilation method, and the results are shown in Table 2. Polyvinyl alcohol was added to each mixture as a binder, and the mixture was granulated in a mortar and then pressure-molded to obtain a ring-shaped compact.

[0057] Each compact was sintered using a method consisting of a temperature-raising process in which the compact was heated from room temperature to the holding temperature shown in Table 2, a high-temperature holding process in which the compact was held at the holding temperature for 1 to 5 hours at an oxygen concentration of 0.86 vol%, and a temperature-lowering process in which the compact was cooled from the holding temperature to room temperature. The oxygen concentration in the sintering atmosphere during the temperature-raising process was 18 vol% from room temperature to 800°C, and 0.1 to 18 vol% after reaching 800°C. During the temperature-lowering process, the oxygen concentration was set to 0.1 to 1.0 vol% at 1050°C and reduced to approximately 0.0024 vol% after 900°C. Each MnZn-based soft ferrite sintered compact was heat-treated at 200°C for 96 hours and then quenched at a rate of 150°C / hr. In this manner, annular MnZn-based soft ferrite cores with an outer diameter of 8 mm, an inner diameter of 4 mm, and a thickness of 2.1 mm were obtained.

[0058] For each MnZn-based soft ferrite core, the density, resistivity ρ, initial permeability μi, relative loss factor tan δ / μ, and core loss Pcv were measured by the following methods.

[0059] (1) Density of Sintered Body The density was calculated from the dimensions and weight of each MnZn-based soft ferrite core by the volume weight method. The results are shown in Table 3.

[0060] (2) Resistivity ρ A flat plate sample was cut out from each MnZn soft ferrite core, silver paste electrodes were attached to two opposing surfaces, and the electrical resistance R (Ω) was measured using a Hioki Milliohm HiTester 3224. The area A (m 2The resistivity ρ (Ω m) was calculated from the thickness t (m) using the following formula (2). The results are shown in Table 3. ρ (Ω m) = R × (A / t) (2)

[0061] (3) Initial magnetic permeability μi After winding seven turns of wire around each MnZn soft ferrite core, a magnetic field of 0.4 A / m was applied and the initial magnetic permeability μi was measured at 23°C and 100 kHz using a Hewlett-Packard HP-4285A. The results are shown in Table 3.

[0062] (4) Relative loss factor tanδ / μ After winding seven turns of wire around each MnZn soft ferrite core, a magnetic field of 0.4 A / m was applied, and the loss factor tanδ and magnetic permeability μ were measured at 23°C and 100 kHz using a Hewlett-Packard HP-4285A, to determine tanδ / μ. The results are shown in Table 3.

[0063] (5) Average grain size The grain boundaries on the mirror-polished surface of each MnZn ferrite sintered body were thermally etched (950-1050°C, 1 hour, treated in N2), then photographed with a scanning electron microscope (1000x magnification), and the average grain size was calculated as the circle-equivalent diameter in a 75 μm x 75 μm square region of the micrograph by quadrature. The results are shown in Table 3.

[0064] (6) Core loss Pcv A primary winding and a secondary winding were wound three turns each around each MnZn soft ferrite core, and the core loss Pcv was measured at -30°C, -15°C, 0°C, 20°C, 40°C, 60°C, 80°C, 100°C, 120°C, 140°C, and 150°C using a BH analyzer (SY-8218) manufactured by Iwasaki Electric Co., Ltd., under conditions of a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. The results are shown in Table 4.

[0065] Note: (1) Percentage (mass%) relative to 100% of the main component.

[0066] Note: (2) Percentage (mass%) of the main component (100 mass%).

[0067] Note: (3) Ratio of mass% of Co3O4 to mole% of Fe2O3. (4) Ratio of square of mass% of Co3O4 to mole% of ZnO.

[0068] Note: (5) Ratio of mass% of Co3O4 to mole% of Fe2O3. (6) Ratio of square of mass% of Co3O4 to mole% of ZnO.

[0069] Note: (7) Measured at 1050°C.

[0070] Note: (8) Measured at 1050°C.

[0071] Notes: (9) Sintered density. (10) Resistivity. (11) Initial permeability at 100 kHz and 0.4 A / m. (12) Relative loss factor at 100 kHz and 0.4 A / m. (13) Average grain size. (14) Not measured.

[0072] Note: (15) to (19) are the same as (9) to (13) in Table 3-1.

[0073] Note: (20) Not measured.

[0074] Note: (21) Maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT max (22) Not measured.

[0075] Note: (23) Not measured.

[0076] Note: (24) Same as (21) in Table 4-2. (25) Not measured.

[0077] As is clear from Table 4, the MnZn-based soft ferrite cores of Examples 1 to 40 all had a maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. max is 3800 kW / m 3In contrast, the MnZn soft ferrite cores of Comparative Examples 1 and 2 had a maximum core loss Pcv of 2 MHz at a frequency of 2 MHz and an excitation flux density of 75 mT between 20 and 100°C. max is 3800 kW / m 3 It was super.

[0078] Each of the MnZn-based soft ferrite cores of Examples 2 to 5 and 7 to 29 and Comparative Example 1 was thermally demagnetized by holding it at 320°C for 1 hour and then cooling it at a rate of -150°C / hr to return it to a state equivalent to the unheated state. Then, the core loss was measured at 20°C to 120°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT using the same method as above. The results are shown in Table 5.

[0079] Note: (26) Maximum core loss Pcv at 20 to 100°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT max .

[0080] Note: (27) Same as (26) in Table 5-1.

[0081] As is clear from Table 5, the MnZn-based soft ferrite cores of Examples 2 to 5 and 7 to 29 after thermal demagnetization all had a maximum core loss Pcv of 1 MHz at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT at 20 to 100°C. max is 3800 kW / m 3 In contrast, the MnZn soft ferrite core of Comparative Example 1 after thermal demagnetization exhibited a maximum core loss Pcv of 1 MHz at a frequency of 1 MHz and an excitation flux density of 100 mT between 20 and 100°C. max is 3800 kW / m 3 It was super.

[0082] Examples 41 to 48 and Comparative Examples 3 to 9: Annular MnZn-based soft ferrite cores with an outer diameter of 8 mm, an inner diameter of 4 mm, and a thickness of 2.1 mm were produced by the same method as in Example 1, except for the compounding ratios shown in Table 6 and the manufacturing conditions shown in Table 7. For each MnZn-based soft ferrite core, the density, resistivity ρ, initial permeability μi, relative loss factor tanδ / μ, and core loss Pcv at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT were measured by the same methods as above. The results are shown in Tables 8 and 9.

[0083] Note: (28) Same as (1) in Table 1-1.

[0084] Note: (29) and (30) are the same as (3) and (4) in Table 1-3.

[0085] Note: (31) Same as (7) in Table 2-1.

[0086] Note: (32) to (36) are the same as (9) to (13) in Table 3-1. (37) Not measured.

[0087] Note: (38) Not measured.

[0088] Note: (39) Same as (21) in Table 4-2.

[0089] As is clear from Table 9, the MnZn-based soft ferrite cores of Examples 41 to 48 all had a maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. max is 3800 kW / m 3 or less, and the core loss was low over a wide temperature range.

[0090] In contrast, the maximum core loss Pcv of Comparative Example 3 and Comparative Example 5, which have a Co content of 0 mass%, at 20 to 100°C max are 11000 kW / m 3 and 10720 kW / m 3 Both are 3800 kW / m 3 It was super.

[0091] In addition, in Comparative Example 4, where the Co content was 0.2 mass% and less than 0.25 mass%, the (Co3O4) / Fe2O3 ratio was 0.0037 and less than 0.00450, and (Co3O4) 2 The ratio of / ZnO is 0.0058, which is less than 0.0135.) The maximum core loss Pcv max is 6325 kW / m 3 and 3800 kW / m 3 Similarly, in Comparative Example 6, in which the Co content was 0.2 mass% and less than 0.25 mass%, the ratio of Co3O4 / Fe2O3 was 0.0036 and less than 0.00450, and (Co3O4) 2 The ratio of / ZnO is 0.0133 and less than 0.0135.) The maximum core loss Pcv max Also, 4745 kW / m 3 and 3800 kW / m 3 In addition, the Pcv at 1 MHz and 100 mT in Comparative Example 6 was max is 3309 kW / m 3 and 3800 kW / m 3 Less than 2 MHz and 75 mT Pcv max is 4745 kW / m 3 and 3800 kW / m 3 The Pcv of the MnZn soft ferrite core of Comparative Example 6 at 2 MHz and 75 mT was max is 4745 kW / m 3 The reason for this large value is thought to be that the Co3O4 content is less than 0.2 mass%.

[0092] In addition, the Zn content was 9.27 mol% in terms of ZnO, exceeding 7 mol% in Comparative Example 7 (the ZnO / Fe2O3 molar ratio was 0.174, exceeding 0.127, and (Co3O4) 2 In Comparative Example 8, in which the Zn content was 9.32 mol % in terms of ZnO and exceeded 7 mol % (the ZnO / Fe2O3 molar ratio was 0.175 and exceeded 0.127), the maximum core loss Pcv max are 5789 kW / m 3and 6057 kW / m 3 Both are 3800 kW / m 3 It was super.

[0093] Furthermore, in Comparative Example 9, the Zn content was 1.04 mol % in terms of ZnO, which was less than 3 mol % (the ZnO / Fe2O3 molar ratio was 0.019, which was less than 0.0541, and (Co3O4) 2 The ratio of ZnO to ZnO is 0.2407, which is more than 0.112.) The maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT max is 4198 kW / m 3 and 3800 kW / m 3 It was super.

[0094] The MnZn soft ferrite cores of Examples 41, 43, and 45, and Comparative Examples 4 and 6 were thermally demagnetized under the same conditions as in Examples 2 to 5 and 7 to 29, and Comparative Example 1, to return them to a state equivalent to the unheated state, and then the core loss was measured at 20°C to 120°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT using the same method as above. The results are shown in Table 10.

[0095] Note: (40) Same as (26) in Table 5-1.

[0096] Example 49: Since the data for Examples 1 to 40 and Comparative Examples 1 and 2 were obtained from long-term heat treatments (96 hours), shorter heat treatment conditions were investigated with productivity in mind. An MnZn-based soft ferrite sintered body was produced using the same method as in Example 1, except for the compounding ratios shown in Table 11 and the manufacturing conditions shown in Table 12. This MnZn-based soft ferrite sintered body was heat-treated at 250°C for 1 hour and then slowly cooled at a rate of 10°C / hr to obtain a ring-shaped MnZn-based soft ferrite core with an outer diameter of 8 mm, an inner diameter of 4 mm, and a thickness of 2.1 mm. The density, resistivity ρ, initial permeability μi, relative loss factor tanδ / μ, and core loss Pcv at a frequency of 2 MHz and an excitation flux density of 75 mT were measured using the same methods as above. The results are shown in Tables 13 and 14.

[0097] Example 50: Since the data for Examples 1 to 40 and Comparative Examples 1 and 2 were obtained from long-term heat treatments of 96 hours, shorter heat treatment conditions were investigated with productivity in mind. An MnZn-based soft ferrite sintered body was produced using the same method as in Example 1, except for the compounding ratios shown in Table 11 and the manufacturing conditions shown in Table 12. This MnZn-based soft ferrite sintered body was heat-treated at 250°C for 11 hours and then quenched at a rate of 150°C / hr to obtain a ring-shaped MnZn-based soft ferrite core with an outer diameter of 8 mm, an inner diameter of 4 mm, and a thickness of 2.1 mm. The density, resistivity ρ, initial permeability μi, relative loss factor tanδ / μ, and core loss Pcv at a frequency of 2 MHz and an excitation flux density of 75 mT of this MnZn-based soft ferrite core were measured using the same methods as above. The results are shown in Tables 13 and 14.

[0098] Note: (41) Same as (1) in Table 1-1.

[0099] Note: (42) and (43) are the same as (3) and (4) in Table 1-3.

[0100] Note: (44) Same as (7) in Table 2-1.

[0101] Note: (45) to (49) are the same as (9) to (13) in Table 3-1. (50) Not measured

[0102]

[0103] Note: (51) Same as (21) in Table 4-2.

[0104] As is clear from Table 14, the MnZn-based soft ferrite cores of Examples 49 and 50 both had a maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. max is 3800 kW / m 3 or less, and the core loss was low over a wide temperature range.

[0105] In Examples 51 and 52, circular MnZn-based soft ferrite cores with an outer diameter of 8 mm, an inner diameter of 4 mm, and a thickness of 2.1 mm were obtained by the same method as in Example 1, except for the compounding ratios shown in Table 15 and the manufacturing conditions shown in Table 16. The density, resistivity ρ, initial permeability μi, relative loss factor tanδ / μ, and core loss Pcv at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT of each MnZn-based soft ferrite core were measured by the same methods as above. The results are shown in Tables 17 and 18.

[0106] Note: (52) Same as (1) in Table 1-1.

[0107] Note: (53) and (54) are the same as (3) and (4) in Table 1-3.

[0108] Note: (55) Same as (7) in Table 2-1.

[0109] Note: (56) to (60) are the same as (9) to (13) in Table 3-1. (61) Not measured.

[0110] Note: (62) Not measured.

[0111] Note: (63) Same as (21) in Table 4-2.

[0112] As is clear from Table 18, the MnZn-based soft ferrite cores of Examples 51 and 52 both had a maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT. max is 3800 kW / m 3 or less, and the core loss was low over a wide temperature range.

[0113] The MnZn soft ferrite cores of Examples 51 and 52 were thermally demagnetized under the same conditions as in Examples 2 to 5 and 7 to 29 and Comparative Example 1 to return them to a state equivalent to the unheated state, and then the core loss was measured at 20°C to 120°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT using the same method as above. The results are shown in Table 19.

[0114] Note: (64) Same as (26) in Table 5-1.

[0115] In Examples 53 to 55, MnZn-based soft ferrite sintered bodies were produced using the same method as in Example 1, except for the compounding ratios shown in Table 20 and the manufacturing conditions shown in Table 21. Circular MnZn-based soft ferrite cores measuring 8 mm in outer diameter, 4 mm in inner diameter, and 2.1 mm in thickness were obtained without heat treatment. The density, resistivity ρ, initial permeability μi, and relative loss factor tanδ / μ of each MnZn-based soft ferrite core were measured using the same methods as above. The results are shown in Table 22. Furthermore, each MnZn-based soft ferrite core was thermally demagnetized under the same conditions as in Examples 2 to 5, 7 to 29, and Comparative Example 1 to return it to a state equivalent to the unheated state. Then, the core loss was measured at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT at temperatures between 20°C and 120°C using the same method as above. The results are shown in Table 23.

[0116] Note: (65) Same as (1) in Table 1-1.

[0117] Note: (66) and (67) are the same as (3) and (4) in Table 1-3.

[0118] Note: (68) Same as (7) in Table 2-1.

[0119] Note: (69) to (73) are the same as (9) to (13) in Table 3-1.

[0120] Note: (74) Same as (26) in Table 5-1.

[0121] As is clear from Table 23, the thermally demagnetized MnZn-based soft ferrite cores of Examples 53 to 55 all exhibited a maximum core loss Pcv at 20 to 100°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT. max is 3800 kW / m 3 or less, and the core loss was low over a wide temperature range.

Claims

1. A composite material containing a main component consisting of 54.0 to 55.5 mol % Fe calculated as Fe2O3, 3 to 7 mol % Zn calculated as ZnO, and the remainder Mn calculated as MnO, and a subcomponent containing 0.25 to 0.7 mol % Co calculated as Co3O4 in outer percent based on 100 mol % of the total of the main components calculated as oxides, and wherein the ratio of the Zn content (mol % calculated as ZnO) to the Fe content (mol % calculated as Fe2O3) in the main component (ZnO / Fe2O3 molar ratio) is 0.0541 to 0.0541. 0.127, the ratio (Co3O4 / Fe2O3 ratio) of the Co content in the minor component (mass % in terms of Co3O4 relative to 100 mass % of the total of the major components) to the Fe content in the major component (mol % in terms of Fe2O3) is 0.00450 to 0.0130, and the ratio of the square of the Co content in the minor component (mass % in terms of Co3O4 relative to 100 mass % of the total of the major components) to the Zn content in the major component (mol % in terms of ZnO) [(Co3O4) 2 / ZnO ratio] is 0.0135 to 0.

112.

2. The MnZn-based soft ferrite according to claim 1, wherein the sintered density is 4.65 g / cm 3 The MnZn-based soft ferrite is characterized by the above.

3. The MnZn-based soft ferrite according to claim 1, characterized in that the average crystal grain size is 2 to 5 μm.

4. In the MnZn-based soft ferrite according to claim 1, the maximum core loss Pcv at 20 to 100°C at a frequency of 2 MHz and an excitation magnetic flux density of 75 mT is max is 3800 kW / m 3 A MnZn-based soft ferrite characterized by the following:

5. In the MnZn-based soft ferrite according to claim 1, the maximum core loss Pcv at 20 to 100°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT is max is 3800 kW / m 3 A MnZn-based soft ferrite characterized by the following:

6. In the MnZn-based soft ferrite according to claim 5, the maximum core loss Pcv at 20 to 100°C at a frequency of 1 MHz and an excitation magnetic flux density of 100 mT is max is 2000 kW / m 3 A MnZn-based soft ferrite characterized by the following:

7. The MnZn-based soft ferrite according to any one of claims 1 to 5, characterized in that the initial permeability μi is 400 or more.

8. A method for producing MnZn-based soft ferrite according to any one of claims 1 to 6, comprising the steps of forming a raw material powder to obtain a molded body, sintering the molded body, and heat-treating the obtained sintered body, wherein the sintering step comprises a high-temperature holding step of holding the material for 1 to 12 hours in an atmosphere having an oxygen concentration of more than 0.05% by volume and not more than 10% by volume at a temperature of more than 1055°C and not more than 1205°C, and wherein the heat treatment step comprises holding the material for 1 hour or more at a temperature that satisfies the condition of (Tc - 100°C) to (Tc - 10°C) (where Tc is the Curie temperature measured by the method specified in JIS C2560-2), and then lowering the temperature from the holding temperature at a cooling rate of 100 to 200°C / hr or at a cooling rate of 50°C / hr or less.

9. A method for producing MnZn-based soft ferrite according to any one of claims 1 to 6, comprising the steps of forming a raw material powder to obtain a compact, and sintering the compact, the sintering step comprising a high-temperature holding step of holding the compact for 1 to 12 hours in an atmosphere having an oxygen concentration of more than 0.05% by volume and not more than 10% by volume at a temperature of more than 1055°C and not more than 1205°C, and wherein no heat treatment is performed after the sintering step.

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