Magnetic core using composite material

Abstract

The present invention relates to a magnetic core using a different type of magnetic material. The magnetic core according to one embodiment may comprise: a ferrite powder comprising manganese (Mn), zinc, iron, and oxygen (O); and a metal alloy powder made of at least two substances from among nickel (Ni), iron (Fe), aluminum (Al), molybdenum (Mo), and silicon (Si). Here, the magnetic core can comprise 67 to 72 wt % of the ferrite powder and 28 to 33 wt % of the metal alloy powder.

Claims

1. A magnetic core comprising: 67 wt % to 72 wt % of ferrite powder comprising manganese (Mn), zinc (Zn), iron (Fe), and oxygen (O); 28 wt % to 33 wt % of metal-alloy powder comprising at least one of nickel (Ni), and iron (Fe), and at least one of aluminum (Al), molybdenum (Mo), and silicon (Si); and a nonmagnetic additive, wherein a difference in molar ratio between the ferrite powder and the metal-alloy powder is less than 5% point, and wherein the ferrite powder and the metal-alloy powder having micrometer-sized particles are bonded with each other, wherein the nonmagnetic additive comprises at least one of silicon oxide (SiO.sub.2), calcium oxide (CaO), tantalum pentoxide (Ta.sub.2O.sub.5), niobium pentoxide (Nb.sub.2O.sub.5), and vanadium pentoxide (V.sub.2O.sub.5), and wherein space between the two kinds of particles is filled with the nonmagnetic additive.

2. The magnetic core according to claim 1, wherein the ferrite powder comprises Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4, and wherein the metal-alloy powder comprises molybdenum permalloy powder (MPP) (Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05).

3. The magnetic core according to claim 1, wherein the metal-alloy powder comprises at least one of FeNi, FeSi, FeAlSi, and NiFeMo.

4. The magnetic core according to claim 1, wherein the magnetic core has a Curie temperature of 300? C. or higher.

5. The magnetic core according to claim 1, wherein the magnetic core has a resonance frequency of 1 MHz or higher.

6. A magnetic core comprising: first ferrite powder comprising (Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4; second ferrite powder comprising Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4; and a nonmagnetic additive, wherein a difference in molar ratio between the first ferrite powder and the second ferrite powder is less than 5% point, wherein the first ferrite powder and the second ferrite powder having micrometer-sized particles are bonded with each other, wherein the nonmagnetic additive comprises at least one of silicon oxide (SiO.sub.2), calcium oxide (CaO), tantalum pentoxide (Ta.sub.2O.sub.5), niobium pentoxide (Nb.sub.2O.sub.5), and vanadium pentoxide (V.sub.2O.sub.5), and wherein space between the two kinds of particles is filled with the nonmagnetic additive.

7. The magnetic core according to claim 6, wherein the magnetic core has a resonance frequency of 1 MHz or higher.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows an example of the binding form of materials constituting a magnetic core according to an embodiment.

(2) FIG. 2 shows an example of the result of X-ray diffraction analysis of the magnetic core according to the embodiment.

(3) FIG. 3 is a graph illustrating the high-temperature characteristic of the magnetic core according to the embodiment.

(4) FIG. 4 is a graph illustrating the high-frequency characteristic of the magnetic core according to the embodiment.

(5) FIG. 5 is a graph illustrating the saturation magnetic flux density characteristic of the magnetic core according to the embodiment.

(6) FIG. 6 is a graph illustrating the direct-current bias characteristic of the magnetic core according to the embodiment.

(7) FIG. 7 is a graph illustrating the high-frequency characteristic of a magnetic core according to another embodiment.

(8) FIG. 8 is a graph illustrating the direct-current bias characteristic of the magnetic core according to the other embodiment.

(9) FIG. 9 is a graph illustrating the high-frequency loss characteristic of the magnetic core according to the other embodiment.

BEST MODE

(10) The present disclosure may be changed in various manners and may have various embodiments, wherein specific embodiments will be described with reference to the drawings. However, the present disclosure is not limited to the specific embodiments, and it should be understood that the present disclosure includes all modifications, equivalents, or substitutions included in the idea and technical scope of the present disclosure.

(11) Although terms including ordinal numbers, such as first and second, may be used herein to describe various components, these components should not be limited by these terms. These terms are only used to distinguish one component from another component. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. The term and/or includes any and all combinations of one or more of the associated listed items.

(12) It should be understood that, when a component is referred to as being connected to or coupled to another component, it may be directly connected to or coupled to another component or intervening components may be present. In contrast, it should be understood that, when a component is referred to as being directly connected to or directly coupled to another component, there are no intervening components present.

(13) In the following description of the embodiments, it will be understood that, when an element, such as a layer (film), a region, a pattern, or a structure is referred to as being on or under another element, such as a substrate, a layer (film), a region, a pad, or a pattern, it can be directly on or under another element or can be indirectly formed such that an intervening element is also present. Terms such as on or under will be described on the basis of the drawings. Also, in the drawings, the thickness or size of a layer (film), a region, a pattern, or a structure may be changed for convenience of description and clarity, and therefore the size thereof does not entirely reflect the actual size thereof.

(14) The terms used in the present application are provided only to described specific embodiments, and do not limit the present disclosure. Singular forms are intended to include plural forms as well, unless the context clearly indicates otherwise. In the present application, it should be understood that the terms includes, has, etc. specify the presence of stated features, numbers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof.

(15) All terms, including technical and scientific terms, have the same meanings as those commonly understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise defined. Commonly used terms, such as those defined in typical dictionaries, should be interpreted as being consistent with the contextual meaning of the relevant art, and are not to be construed in an ideal or overly formal sense unless expressly defined to the contrary.

(16) In one embodiment, there is provided a magnetic core including a ferrite-based material and a metal-based material.

(17) In one aspect of this embodiment, the ferrite-based material may be a MnZn-based ferrite. For example, the ferrite-based material may be MnZnFe.sub.2O.sub.4.

(18) The metal-based material may be an alloy material including two or more of nickel (Ni), iron (Fe), aluminum (Al), molybdenum (Mo), and silicon (Si). For example, the metal-based material may be permalloy (FeNi), ferrosilicon (FeSi), FeAlSi, or NiFeMo.

(19) Also, in one aspect of this embodiment, the ferrite-based material and the metal-based material may have the same molar ratios in order to constitute a magnetic core.

(20) Also, in one aspect of this embodiment, a microscopic powder type ferrite-based material and a microscopic powder type metal-based material may be mixed with a nonmagnetic additive and may then be thermally treated so as to be manufactured as a magnetic core.

(21) Hereinafter, the composition and characteristics of a magnetic core according to an embodiment will be described in detail with reference to the accompanying drawings. Identical or corresponding components will be denoted by the same reference numerals irrespective of the drawings, and a duplicate description thereof will be omitted.

(22) First, the main composition of the magnetic core according to the embodiment will be described with reference to Tables 1 and 2 below.

(23) TABLE-US-00001 TABLE 1 Content ratio Content ratio Category Composite (molar ratio %) (wt %) Main Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 50% 67 to 72% composition Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05 50% 28 to 33% (Magnetic Total 100% Powder)

(24) Referring to Table 1, the magnetic core according to the embodiment may include Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 as a ferrite-based material, which is one constituent of the main composition, and molybdenum permalloy powder (MPP) (Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05) as a metal-alloy-based material, which is the other constituent of the main composition. Here, Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 may be a material including 67% of manganese (Mn), 23% of zinc (Zn), 9% of iron (Fe), and the remainder of oxygen (O).

(25) The two materials may have the same molar ratios. That is, the molar ratio of each of the two materials may be 50%. Also, in terms of weight ratio (wt %), the magnetic core may include 67% to 72% of Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 and 28% to 33% of Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05.

(26) Depending on embodiments, the metal-alloy-based material, Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05, may be replaced with Ni.sub.0.81Fe.sub.0.19, Fe.sub.3Al.sub.0.33Si.sub.0.67, FeSi, or a mixture thereof having the same molar ratios. For example, in the case in which Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05 is replaced with a mixture of Ni.sub.0.81Fe.sub.0.19, Fe.sub.3Al.sub.0.33Si.sub.0.67, and FeSi, the composition shown in Table 2 below, including Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4, may be provided.

(27) TABLE-US-00002 TABLE 2 Content ratio Category Composite (molar ratio %) MnZn ferrite Main Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 50% Powder + Metal composition Ni.sub.81Fe.sub.19 15.60% alloy Powder Ni.sub.79Fe.sub.16Mo.sub.5 14.40% Fe.sub.3Al.sub.0.33Si.sub.0.67 10% FeSi 10% Total 100%

(28) Of course, the ratios between the metal alloys shown in Table 2 are illustrative. In another embodiment, the relative ratios may be changed within a range within which a total molar ratio is maintained, and at least some metal alloys may be excluded. Next, the nonmagnetic additive will be described with reference to Table 3 below.

(29) TABLE-US-00003 TABLE 3 Content concentration Content ratio Category Composite (ppm based on 1 kg) (wt %) Nonmagnetic SiO.sub.2 80 to 120 ppm <0.1% additive CaO 80 to 100 ppm <0.1% Ta.sub.2O.sub.5 300 to 400 ppm <0.1% Nb.sub.2O.sub.5 200 to 300 ppm <0.1% V.sub.2O.sub.5 200 to 300 ppm <0.1%

(30) Referring to Table 3, the magnetic core according to the embodiment may include at least one of silicon oxide (SiO.sub.2), calcium oxide (CaO), tantalum pentoxide (Ta.sub.2O.sub.5), niobium pentoxide (Nb.sub.2O.sub.5), and vanadium pentoxide (V.sub.2O.sub.5), each of which is a nonmagnetic additive, in addition to the main composition. The nonmagnetic additive may serve to maintain force of binding between the ferrite-based powder and the metal-ally-based powder after heat treatment. A method of manufacturing the magnetic core having the above-described composition is as follows.

(31) First, ferrite-based powder and metal-alloy-based powder having a particle size of several ?m to several tens of ?m are prepared so as to have the same molar ratios. Each powder may be manufactured by water atomization or gas atomization. However, the present disclosure is not limited thereto.

(32) The nonmagnetic additive shown in Table 3 is uniformly mixed therewith, and the mixture is shaped at a high pressure (e.g. 10 to 20 tons/cm.sup.2) to form a magnetic core having a desired shape. The magnetic core may be a toroidal-type core, an E-type core, a pq-type core, an EPC-type core, or an I-type core. However, the present disclosure is not limited thereto.

(33) The magnetic core formed through high-pressure shaping may be thermally treated at a high temperature (e.g. 600? C. or higher) for a predetermined time in order to remove residual stress and deformation therefrom.

(34) The disposition state of the composites of the magnetic core formed as the result of heat treatment is shown in FIG. 1.

(35) FIG. 1 shows an example of the binding form of materials constituting a magnetic core according to an embodiment. In FIG. 1, there is shown an enlarged shape of one section 11 of a toroidal-type magnetic core 10.

(36) Referring to FIG. 1, in the magnetic core 10 according to the embodiment, particles of ferrite-based powder 100 and metal-alloy-based powder 200 are mixed with each other, and the space between the two kinds of particles is filled with a nonmagnetic additive 300. Due to binding between such micrometer-sized particles, the magnetic core according to the embodiment has a uniform magnetic characteristic and high mechanical strength, compared to a structure in which cores each made of a general ferrite-based material and cores each made of a metal-alloy-based material are alternately stacked.

(37) In the magnetic core according to the embodiment, individual particles are mixed with each other in the state in which inherent characteristics thereof are maintained without being synthesized into a third material through reaction even after high-pressure shaping and heat treatment are performed. This state may be verified through X-ray diffraction (XRD) analysis.

(38) FIG. 2 shows an example of the result of X-ray diffraction analysis of the magnetic core according to the embodiment.

(39) In FIG. 2, there is shown an X-ray diffraction analysis graph of the magnetic core according to the embodiment. This result is the result of analysis of a magnetic core formed by mixing Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 and MPP(Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05) with each other so as to have the same molar ratios and shaping the mixture.

(40) Referring to FIG. 2, it can be seen that the MnZn ferrite phase and the MPP phase are simultaneously detected in an XRD pattern, which means that the two materials are mixed with each other in the state of not being denatured without forming a third phase through reaction therebetween.

(41) Hereinafter, various characteristics of the magnetic core according to the embodiment will be described with reference to FIGS. 3 to 6 so as to be compared with comparative examples. In the following description, a first comparative example is a magnetic core using a general MnZn ferrite without a metal alloy, a second comparative example is a magnetic core using a general metal alloy without a MnZn ferrite, and the embodiment is a magnetic core formed by mixing Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 and MPP(Ni.sub.0.79Fe.sub.0.16Mo.sub.0.05) with each other so as to have the same molar ratios and shaping the mixture.

(42) First, a high-temperature characteristic will be described with reference to FIG. 3.

(43) FIG. 3 is a graph illustrating the high-temperature characteristic of the magnetic core according to the embodiment. In FIG. 3, the horizontal axis indicates temperature, and the vertical axis indicates initial permeability (pi).

(44) Referring to FIG. 3, the magnetic characteristic of the magnetic core according to the first comparative example substantially disappears at 250? C. or higher. This results from the fact that the Curie temperature of the MnZn ferrite is low. In addition, the magnetic core according to the second comparative example has a relatively uniform magnetic characteristic even at 400? C. or higher but has excessively low initial permeability even at a low temperature. In contrast, the magnetic core according to the embodiment maintains an initial permeability of 500 or more at 250? C. or lower, and has a meaningful magnetic characteristic at a high temperature of 300? C. or higher, since Curie temperature thereof exceeds 300? C. Consequently, the magnetic core according to the embodiment has high initial permeability at a low temperature, compared to the second comparative example, and has a characteristic in which an available region thereof is increased in a high temperature, compared to the first comparative example.

(45) Next, a high-frequency characteristic will be described with reference to FIG. 4.

(46) FIG. 4 is a graph illustrating the high-frequency characteristic of the magnetic core according to the embodiment. In FIG. 4, the horizontal axis indicates frequency, and the vertical axis indicates initial permeability (pi).

(47) Referring to FIG. 4, the magnetic core according to the second comparative example has relatively uniform initial permeability even at a high frequency of 1 MHz or higher, but the magnitude thereof is about half that of the first comparative example. In addition, the magnetic core according to the first comparative example has relatively excellent initial permeability at a frequency of 1 MHz or lower, but the performance thereof is abruptly reduced in a MHz range, since the resonance point thereof is located at about 1 MHz (410). In contrast, it can be seen that the resonance point of the magnetic core according to the embodiment moves farther to a high-frequency region, compared to the first comparative example, whereby the magnetic core according to the embodiment is usable even after a frequency limit point (i.e. 1 MHz), compared to a magnetic core made of a general MnZn-based ferrite material, and reduction in performance due to an increase in frequency is small.

(48) As described with reference to FIGS. 3 and 4, therefore, the magnetic core according to the embodiment is also applicable to a passive device configured to be operated at a high temperature of 300? C. or higher and a high frequency of 1 MHz or higher.

(49) Next, direct-current (DC) bias performance will be described with reference to FIGS. 5 and 6.

(50) FIG. 5 is a graph illustrating the saturation magnetic flux density characteristic of the magnetic core according to the embodiment, and FIG. 6 is a graph illustrating the direct-current bias characteristic of the magnetic core according to the embodiment.

(51) In FIG. 5, the horizontal axis indicates magnetic field, and the vertical axis indicates magnetic flux density. Referring to FIG. 5, it can be seen that the magnetic flux density of the magnetic core according to the embodiment is greatly increased, compared to the first comparative example, whereby saturation is not easily achieved. Consequently, high direct-current bias performance is expected. This appears more clearly in FIG. 6.

(52) In FIG. 6, the lower end of the horizontal axis indicates magnetizing force, the upper end of the horizontal axis indicates direct-current bias current, and the vertical axis indicates inductance.

(53) Referring to FIG. 6, it can be seen that, around an arrow, the magnetic core according to the embodiment has high inductance, compared to the magnetic core according to the second comparative example, and has improved direct-current bias performance, compared to the magnetic core according to the first comparative example. In other words, maximum current is increased, compared to the first comparative example. This means that direct-current bias performance can be improved from about 3 A to about 14 A.

(54) Advantages of the magnetic core according to the embodiment described above may be summarized as follows.

(55) A general MnZn ferrite-based magnetic core has a low available temperature range and a low available frequency, whereas the magnetic core according to the embodiment is also applicable to a passive device configured to be operated at a high temperature of 300? C. or higher and a high frequency of 1 MHz or higher through mixing with metal-alloy powder.

(56) Also, the magnetic flux density of the general MnZn ferrite-based magnetic core is rapidly saturated due to a low Bs value, whereby the direct-current bias performance thereof is low, whereas the magnetic core according to the embodiment has higher direct-current bias performance through mixing with metal-alloy powder.

(57) In addition, a general hybrid core formed by stacking individual magnetic cores made of different kinds of materials has low mechanical strength due to the junction between the different kinds of cores and has different magnetic characteristics depending on the position thereof, whereas the magnetic core according to the embodiment has a uniform magnetic characteristic and high mechanical strength through microscopic mixing composition.

(58) Meanwhile, in the previous embodiment, the ferrite-based material and the metal-based material were described as being included in the magnetic core so as to have the same molar ratios. However, the present disclosure is not limited thereto. For example, depending on embodiments, the molar ratios of the ferrite-based material and the metal-based material may have a difference of less than 5% therebetween.

(59) As an example, in the magnetic core, the molar ratio of the ferrite powder may be 52%, and the molar ratio of the metal-alloy powder may be 48%. That is, on the assumption that the sum of the molar ratio of the ferrite powder and the molar ratio of the metal-alloy powder is 100%, the difference between the molar ratios thereof is less than 5% point.

(60) In the magnetic core, the difference between the molar ratios may be adjusted based on a characteristic necessary to be further strengthened depending on design purposes, among ferrite-based characteristics and the metal-alloy-based characteristics. For example, in the case in which the molar ratio of the ferrite powder is greater than the molar ratio of the metal-alloy powder, better initial permeability is exhibited at the same temperature and the same frequency, compared to a molar ratio of 1:1 (i.e. the same molar ratios). On the other hand, in the case in which the molar ratio of the metal-alloy powder is greater than the molar ratio of the ferrite powder, an available region moves to a higher temperature and has a higher resonance frequency than in the same molar ratios.

(61) In another embodiment, a magnetic core including different kinds of ferrite-based materials is provided.

(62) In one aspect of this embodiment, one ferrite-based material may be a MnZn-based ferrite, and the other ferrite-based material may be a NiZn-based ferrite. For example, the MnZn-based ferrite material may be MnZnFe.sub.2O.sub.4, and the NiZn-based ferrite material may be NiZnFe.sub.2O.sub.4. More specifically, the MnZn-based ferrite material may be Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4, and the NiZn-based ferrite material may be Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4.

(63) Also, in one aspect of this embodiment, the different kinds of ferrite-based materials may have predetermined molar ratios in order to constitute a magnetic core. For example, the different kinds of ferrite-based materials may have the same molar ratios.

(64) Also, in one aspect of this embodiment, different kinds of microscopic powder type ferrite-based materials may be mixed with a nonmagnetic additive and may then be thermally treated so as to manufacture a magnetic core.

(65) Hereinafter, the composition and characteristics of a magnetic core according to another embodiment will be described in detail with reference to the accompanying drawings. Identical or corresponding components will be denoted by the same reference numerals irrespective of the drawings, and a duplicate description thereof will be omitted.

(66) First, the composition of the magnetic core according to the other embodiment will be described with reference to Table 4 below.

(67) TABLE-US-00004 TABLE 4 Content ratio Classification Category Constituent (molar ratio %) MnZn-based Main Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 50% ferrite composition Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4 50% powder + (Magnetic Total 100% NiZn-based powder) ferrite powder Nonmagnetic SiO.sub.2 80 to 120 ppm additive CaO 80 to 100 ppm Ta.sub.2O.sub.5 300 to 400 ppm Nb.sub.2O.sub.5 200 to 300 ppm V.sub.2O.sub.5 200 to 300 ppm

(68) Referring to Table 4, the magnetic core according to the other embodiment may include Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 and Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4 as different kinds of ferrite-based materials, which are constituents of the main composition. Here, Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 may be a material including 67% of manganese (Mn), 23% of zinc (Zn), 9% of iron (Fe), and the remainder of oxygen (O), and Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4 may be configured such that the ratio of nickel:zinc is 6:4. As shown in Table 4, the two ferrite materials may have the same molar ratios. That is, the molar ratio of each of the two materials may be 50%. However, the present disclosure is not limited thereto. That is, depending on embodiments, the molar ratios of the two materials may have a difference of less than 5% point. In other words, on the assumption that the sum of the molar ratios of the two materials is 100%, the difference between the molar ratios thereof is less than 5% point.

(69) For example, in the magnetic core, the molar ratio of Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 may be 52%, and the molar ratio of Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4 may be 48%. As another example, in the magnetic core, the molar ratio of Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 may be 49%, and the molar ratio of Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4 may be 51%.

(70) In the magnetic core, the difference between the molar ratios may be adjusted based on a characteristic necessary to be further strengthened depending on design purposes, among MnZn ferrite-based characteristics and NiZn ferrite-based characteristics. For example, in the case in which the molar ratio of the MnZn ferrite powder is greater than the molar ratio of the NiZn ferrite powder, better initial permeability is exhibited at the same frequency, compared to a molar ratio of 1:1 (i.e. the same molar ratios), as will be described below. On the other hand, in the case in which the molar ratio of the NiZn ferrite powder is greater than the molar ratio of the MnZn ferrite powder, an available region moves to a higher temperature and has a higher resonance frequency than in the same molar ratios.

(71) In addition, as shown in Table 4, the magnetic core according to the other embodiment may include at least one of silicon oxide (SiO.sub.2), calcium oxide (CaO), tantalum pentoxide (Ta.sub.2O.sub.5), niobium pentoxide (Nb.sub.2O.sub.5), and vanadium pentoxide (V.sub.2O.sub.5), each of which is a nonmagnetic additive, in addition to the main composition. The nonmagnetic additive may serve to maintain force of binding between the different kinds of ferrite-based powders after heat treatment.

(72) A method of manufacturing the magnetic core having the above-described composition is as follows.

(73) First, different kinds of ferrite-based powders having a particle size of several ?m to several tens of ?m are prepared so as to have predetermined molar ratios (e.g. the same molar ratios). Each powder may be manufactured by water atomization or gas atomization. However, the present disclosure is not limited thereto.

(74) The nonmagnetic additive shown in Table 4 is uniformly mixed therewith, and the mixture is shaped at a high pressure (e.g. 10 to 20 tons/cm.sup.2) to form a magnetic core having a desired shape. The magnetic core may be a toroidal-type core, an E-type core, a pq-type core, an EPC-type core, or an I-type core. However, the present disclosure is not limited thereto.

(75) The magnetic core formed through high-pressure shaping may be thermally treated at a high temperature (e.g. 600? C. or higher) for a predetermined time in order to remove residual stress and deformation therefrom.

(76) The disposition state of the composites of the magnetic core formed as the result of heat treatment may be similar to the state shown in FIG. 1. For example, in the magnetic core according to the other embodiment, particles of the MnZn-based ferrite powder and the NiZn-based ferrite powder are mixed with each other, and the space between the two kinds of particles is filled with a nonmagnetic additive. Due to binding between such micrometer-sized particles, the magnetic core according to the other embodiment has a uniform magnetic characteristic and high mechanical strength, compared to a structure in which general different kinds of ferrite-based materials are alternately stacked.

(77) In the magnetic core according to the other embodiment, individual particles may be mixed with each other in the state in which inherent characteristics thereof are maintained without being synthesized into a third material through reaction even after high-pressure shaping and heat treatment are performed.

(78) Hereinafter, various characteristics of the magnetic core according to the other embodiment will be described with reference to FIGS. 7 to 9 so as to be compared with comparative examples. In the following description, a third comparative example is a magnetic core using a general MnZn ferrite without a metal alloy, a fourth comparative example is a magnetic core using a MnZn ferrite, and the other embodiment is a magnetic core formed by mixing Mn.sub.0.67Zn.sub.0.23Fe.sub.2.09O.sub.4 and Ni.sub.0.6Zn.sub.0.4Fe.sub.2O.sub.4 with each other so as to have the same molar ratios and shaping the mixture.

(79) First, a high-frequency characteristic will be described with reference to FIG. 7.

(80) FIG. 7 is a graph illustrating the high-frequency characteristic of the magnetic core according to the other embodiment. In FIG. 4, the horizontal axis indicates frequency, and the vertical axis indicates initial permeability (pi).

(81) Referring to FIG. 7, the magnetic core according to the fourth comparative example has relatively uniform initial permeability even at a high frequency of 1 MHz or higher, but the magnitude thereof is about half of that of the third comparative example. In addition, the magnetic core according to the third comparative example has relatively excellent initial permeability at a frequency of 1 MHz or lower, but the performance thereof is abruptly reduced in a MHz range, since the resonance point R1 thereof is located at about 1 MHz. In contrast, it can be seen that the resonance point RE of the magnetic core according to the other embodiment moves farther to a high-frequency region, compared to the third comparative example, whereby the magnetic core according to the embodiment is usable even above a frequency limit point (i.e. 1 MHz), compared to a magnetic core made of a general MnZn-based ferrite material, and reduction in performance due to increase in frequency is small. In addition, the magnetic core according to the other embodiment has low reduction in permeability (about 10%) while having an excellent high-frequency characteristic, compared to the third comparative example, and has permeability equivalent to about twice that of the fourth comparative example.

(82) Consequently, the magnetic core according to the other embodiment is also applicable to a passive device configured to be operated at a high frequency of 1 MHz or higher while having excellent initial permeability

(83) Next, direct-current (DC) bias performance will be described with reference to FIG. 8.

(84) FIG. 8 is a graph illustrating the direct-current bias characteristic of the magnetic core according to the other embodiment.

(85) In FIG. 8, the horizontal axis indicates magnetizing force, and the vertical axis indicates inductance.

(86) Referring to FIG. 8, the magnetic core according to the third comparative example has relatively high inductance in a specific magnetizing force range (i.e. 150 Oe or lower), but the inductance thereof is abruptly reduced when deviating from the range, whereby power reception capacity is limited. In addition, the inductance of the magnetic core according to the fourth comparative example is maintained even at high magnetizing force; but the value of inductance is very low. In contrast, the magnetic core according to the other embodiment has high inductance within most of the magnetizing force range, compared to the fourth comparative example, and the inductance of the magnetic core is maintained high even within a range of 150 Oe or higher, compared to the third comparative example, whereby the magnetic core according to the other embodiment has excellent inductance within a wide magnetizing force range. In other words, the magnetic core according to the other embodiment has higher inductance than the magnetic core according to the fourth comparative example within a magnetizing force range of less than 250 Oe, and exhibits improved direct-current bias performance within the magnetizing force range, compared to the magnetic core according to the third comparative example.

(87) Meanwhile, one of the losses caused in a passive device in a high-frequency environment is eddy current loss. Since eddy current loss is proportional to the square of frequency, the eddy current loss acts as a predominant loss component in the case in which the frequency used is increased. Consequently, in the aspect of the eddy current loss, low power density in a high-frequency range (e.g. 0.5 MHz or higher) is advantageous. Such a high-frequency loss characteristic will be described with reference to FIG. 9.

(88) FIG. 9 is a graph illustrating the high-frequency loss characteristic of the magnetic core according to the other embodiment.

(89) Referring to FIG. 9, there is shown frequency-based power density of each of the magnetic cores according to the third comparative example, the fourth comparative example, and the other embodiment. In FIG. 9, the horizontal axis indicates frequency, and the vertical axis indicates power density.

(90) As shown, three different power densities intersect each other at about 0.4 MHz. The magnetic core according to the third comparative example exhibits low power density at a low-frequency range based on 0.4 MHz but has high power density at a high-frequency range. Consequently, the magnetic core according to the third comparative example is not suitable for a high-frequency environment. In addition, the magnetic core according to the fourth comparative example exhibits low power density at a high-frequency range but has high power density at a low-frequency range. Consequently, application of the magnetic core according to the fourth comparative example to a range other than a high-frequency range is difficult. In contrast, the magnetic core according to the other embodiment exhibits uniform performance over the entire frequency range, whereby there is little effect due to frequency change in the aspect of eddy current loss.

(91) Advantages of the magnetic core according to the other embodiment described above may be summarized as follows.

(92) A general MnZn ferrite-based magnetic core has a low available frequency, whereas the magnetic core according to the other embodiment also has characteristics of a NiZn ferrite and is thus also applicable to a passive device configured to be operated at a high frequency of 1 MHz or higher.

(93) Also, the inductance of the general MnZn ferrite-based magnetic core is rapidly reduced when exceeding specific magnetic force and thus has low direct-current bias performance, whereas the magnetic core according to the other embodiment also has characteristics of the NiZn ferrite, whereby power reception capacity thereof is increased and thus the magnetic core according to the other embodiment has higher direct-current bias performance.

(94) Also, the magnetic core according to the other embodiment has both MnZn ferrite-based characteristics and NiZn ferrite-based characteristics in the entire frequency range, whereby an operating frequency environment is little affected even in the aspect of eddy current loss.

(95) In addition, a general hybrid core formed by stacking individual magnetic cores made of different kinds of materials has low mechanical strength due to the junction between the different kinds of cores and has magnetic characteristics different depending on the position thereof, whereas the magnetic core according to the other embodiment has a uniform magnetic characteristic and high mechanical strength through microscopic mixing composition.

(96) A description of each of the above embodiments is applicable to another embodiment, unless they conflict with each other.

(97) Although embodiments have been described above, the embodiments are merely illustrations and do not limit the present disclosure, and those skilled in the art will appreciate that various modifications and applications are possible without departing from the intrinsic features of the disclosure. For example, concrete constituent elements of the embodiments may be modified. In addition, it is to be understood that differences relevant to the modifications and the applications fall within the scope of the present disclosure defined in the appended claims.