阅读说明：本技术 铁氧体磁芯和包含所述铁氧体磁芯的线圈部件 (Ferrite core and coil component including the same ) 是由 李贤智 廉载勋 金成勋 裵硕 李相元 于 2019-01-28 设计创作，主要内容包括：根据本发明的一个实施方式的铁氧体磁芯包含：多个晶粒,所述多个晶粒含有30摩尔％-40摩尔％的Mn、5摩尔％-15摩尔％的Zn和50摩尔％-60摩尔％的Fe；以及在所述多个晶粒之间的多个晶界,其中所述多个晶粒和所述多个晶界含有Co、Ni、SiO<Sub>2</Sub>、CaO和Ta<Sub>2</Sub>O<Sub>5</Sub>,其中在所述多个晶粒内部Co和Ni的含量是在所述多个晶界中Co和Ni的含量的至少两倍,其中在所述多个晶界中SiO<Sub>2</Sub>、CaO和Ta<Sub>2</Sub>O<Sub>5</Sub>的含量是在所述多个晶粒内部SiO<Sub>2</Sub>、CaO和Ta<Sub>2</Sub>O<Sub>5</Sub>的含量的至少两倍,并且其中所述铁氧体磁芯具有3000以上的磁导率和800以下的磁芯损耗。(A ferrite core according to an embodiment of the present invention includes: a plurality of grains containing 30-40 mol% Mn, 5-15 mol% Zn, and 50-60 mol% Fe; and a plurality of grain boundaries between the plurality of crystal grains, wherein the plurality of crystal grains and the plurality of grain boundaries contain Co, Ni, SiO 2 CaO and Ta 2 O 5 Wherein Co and Ni are present inside the plurality of grainsA content of at least two times that of Co and Ni in the plurality of grain boundaries in which SiO is present 2 CaO and Ta 2 O 5 Is SiO in the inside of the plurality of crystal grains 2 CaO and Ta 2 O 5 And wherein the ferrite core has a permeability of 3000 or more and a core loss of 800 or less.)

1. A ferrite core, comprising:

a plurality of grains comprising 30 to 40 mol% Mn, 5 to 15 mol% Zn, and 50 to 60 mol% Fe; and

a plurality of grain boundaries between the plurality of grains,

wherein the plurality of grains and the plurality of grain boundaries comprise Co, Ni, SiO₂CaO and Ta₂O₅，

The content of Co and Ni in the plurality of grains is more than twice the content of Co and Ni in the plurality of grain boundaries,

the SiO in the plurality of grain boundaries₂The CaO and the Ta₂O₅In an amount of the SiO in the plurality of crystal grains₂The CaO andta described₂O₅Is more than twice of the content of (A) in the composition,

a magnetic permeability of 3000 or more, and

the core loss is 800 or less.

2. The ferrite core of claim 1, wherein:

the plurality of grains and the plurality of grain boundaries further comprise Nb₂O₅And V₂O₅(ii) a And is

And said Nb in said plurality of grains₂O₅And said V₂O₅In comparison with the content of (A) of (B), said Nb₂O₅And said V₂O₅Is distributed in a higher content in the plurality of grain boundaries.

3. The ferrite core according to claim 1, wherein the SiO is contained in an amount of 1ppm to 200ppm₂。

4. The ferrite core according to claim 3, wherein the SiO is contained in an amount of 50ppm to 150ppm₂。

5. The ferrite core according to claim 1, wherein an average spacing between the plurality of grains is in a range of 0.5 μm to 3 μm.

6. The ferrite core according to claim 5, wherein an average spacing between the plurality of grains is in a range of 1 μm to 2 μm.

7. The ferrite core according to claim 5, wherein an average particle diameter of the plurality of crystal grains is in a range of 3 μm to 16 μm.

8. The ferrite core according to claim 7, wherein an average particle diameter of the plurality of crystal grains is in a range of 7 μm to 12 μm.

9. A coil component comprising:

a Mn-Zn type ferrite core; and

a coil wound around the Mn-Zn type ferrite core,

wherein the Mn-Zn type ferrite core comprises a plurality of crystal grains comprising 30 to 40 mol% of Mn, 5 to 15 mol% of Zn, and 50 to 60 mol% of Fe; and a plurality of grain boundaries between the plurality of grains,

the plurality of grains and the plurality of grain boundaries comprise Co, Ni, SiO₂CaO and Ta₂O₅，

The content of Co and Ni in the plurality of grains is more than twice the content of Co and Ni in the plurality of grain boundaries,

the SiO in the plurality of grain boundaries₂The CaO and the Ta₂O₅In an amount of the SiO in the plurality of crystal grains₂The CaO and the Ta₂O₅Is more than twice of the content of (A) in the composition,

a magnetic permeability of 3000 or more, and

the core loss is 800 or less.

10. The coil component of claim 9, wherein:

an average pitch between the plurality of crystal grains is in a range of 0.5 μm to 3 μm; and is

The plurality of crystal grains have an average grain diameter in a range of 3 μm to 16 μm.

Technical Field

The present invention relates to a ferrite core, and more particularly, to a ferrite core and a coil component including the same.

Background

With the development of vehicle-related technologies, there is growing interest in the technology of vehicle electrical components. Technologies of vehicle electrical components can be mainly classified into vehicle semiconductor technologies, telematics technologies, vehicle display technologies, battery technologies, motor technologies, camera module technologies, and the like. The vehicle electrical component may include an inductor, a choke coil, a transformer, a motor, a transformer for a Direct Current (DC)/DC converter, an electromagnetic interference (EMI) shielding member, and the like, and may necessarily include a coil part including a ferrite core and a coil.

Generally, the magnetic properties required for ferrite cores are high permeability and low core loss. In order to obtain the magnetic properties, the composition for ferrite cores may further include various additives in addition to the main material contained in the ferrite core.

However, some additives are used to improve the magnetic properties of the ferrite core, but may increase the grain boundaries between grains in the ferrite core. When grain boundaries between crystal grains increase in the ferrite core, the strength and formability of the ferrite core decrease, and therefore, there is a problem that the reliability of the ferrite core decreases.

Disclosure of Invention

[ problem ] to

The present invention aims to provide a ferrite core having excellent magnetic properties and formability and a coil component including the ferrite core.

[ solution ]

One aspect of the present invention provides a ferrite core comprising a plurality of crystal grains comprising 30 to 40 mol% of Mn, 5 to 15 mol% of Zn, and 50 to 60 mol% of Fe; and a plurality of grain boundaries between the plurality of grains, wherein the plurality of grains and the plurality of grain boundaries comprise Co, Ni, SiO₂CaO and Ta₂O₅The content of Co and Ni in the plurality of crystal grains is more than twice of the content of Co and Ni in the plurality of crystal boundaries, and SiO in the plurality of crystal boundaries₂CaO and Ta₂O₅In an amount of SiO in the plurality of grains₂CaO and Ta₂O₅Is more than two times the content of (b), the magnetic permeability is more than 3000, and the core loss is 800 or less.

The plurality of grains and the plurality of grain boundaries may further include Nb₂O₅And V₂O₅And Nb in said plurality of crystal grains₂O₅And V₂O₅Content ratio of (B) Nb₂O₅And V₂O₅May be distributed in a higher content in the plurality of grain boundaries.

May contain 1ppm to 200ppm of SiO₂。

May contain 50ppm to 150ppm of SiO₂。

May contain from 1500ppm to 5500ppm of Co.

May contain 300ppm to 500ppm of Ni.

CaO may be included in an amount of 400ppm to 600 ppm.

May contain 400 to 600ppm of Ta₂O₅。

May contain 250ppm to 400ppm Nb₂O₅。

May contain V in the range of 400ppm to 600ppm₂O₅。

The average pitch between the plurality of grains may be in a range of 0.5 μm to 3 μm.

The average pitch between the plurality of crystal grains may be in a range of 1 μm to 2 μm.

The plurality of crystal grains may have an average grain diameter in a range of 3 μm to 16 μm.

The plurality of crystal grains may have an average grain diameter in a range of 7 μm to 12 μm.

An aspect of the present invention provides a coil component comprising a Mn-Zn based ferrite core and a coil wound around the Mn-Zn based ferrite core, wherein the Mn-Zn based ferrite core comprises a plurality of crystal grains comprising 30 to 40 mol% of Mn, 5 to 15 mol% of Zn, and 50 to 60 mol% of Fe; and a plurality of grain boundaries between the plurality of grains, the plurality of grains and the plurality of grain boundaries comprising Co, Ni, SiO₂CaO and Ta₂O₅The content of Co and Ni in the plurality of crystal grains is more than twice of the content of Co and Ni in the plurality of crystal boundaries, and SiO in the plurality of crystal boundaries₂CaO and Ta₂O₅In an amount of SiO in the plurality of grains₂CaO and Ta₂O₅Is more than two times the content of (b), the magnetic permeability is more than 3000, and the core loss is 800 or less.

[ advantageous effects ]

According to the embodiments of the present invention, a ferrite core having high permeability and low core loss can be obtained. In particular, the ferrite core according to the embodiment of the present invention can have excellent magnetic properties such as permeability and core loss, high strength, and excellent formability and machinability. The ferrite core according to the embodiment of the present invention may be variously applied to vehicles or industrial applications.

Drawings

Fig. 1 is a view showing one example of a coil component according to one embodiment of the present invention.

FIG. 2 is an enlarged view illustrating a portion of a ferrite core according to one embodiment of the present invention.

FIG. 3 is an image of a ferrite core taken by an optical microscope in accordance with one embodiment of the present invention.

FIG. 4 is a graph of the content of some additives in a ferrite core according to one embodiment of the present invention.

FIG. 5 is a graph of the content of the remaining additives in the ferrite core according to one embodiment of the present invention.

Fig. 6 is a flowchart illustrating a method of manufacturing a ferrite core according to an embodiment of the present invention.

Fig. 7 is a set of images taken by an optical microscope of example 3, example 4, comparative example 1, and comparative example 2.

Detailed Description

Since the invention is susceptible to various modifications and embodiments, specific embodiments have been shown in the drawings and will be described in detail in the written description. However, this is not intended to limit the present invention to the specific embodiments, and it should be understood that all changes, equivalents and alternatives falling within the spirit and technical scope of the present invention are encompassed by the present invention.

Although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and a second element could similarly be termed a first element, without departing from the scope of the present invention. As used herein, the term "and/or" includes a combination or any of a number of the associated listed items.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

The terminology used herein to describe embodiments of the invention is not intended to limit the scope of the invention. As used in this specification, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, components, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof.

Unless defined otherwise, all terms used herein including technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Unless otherwise explicitly defined herein, terms defined in commonly used dictionaries are to be interpreted as including meanings identical to the contextual meanings of the related art, but are not to be interpreted in an idealized or overly formal sense.

Embodiments of the present invention will be described in more detail hereinafter with reference to the accompanying drawings. The same or corresponding components to each other are denoted by the same reference numerals regardless of the reference numerals, and redundant description will be omitted.

Fig. 1 is a view showing one example of a coil component according to one embodiment of the present invention.

Referring to fig. 1, a coil component 100 includes a ferrite core 110 and a coil 120 wound around the ferrite core 110. In this case, the ferrite core 110 may have a ring shape, and the coil 120 may include a first coil 122 wound around the ferrite core 110 and a second coil 124 wound around the ferrite core 110 to be symmetrical to the first coil 122. The first and second coils 122 and 124 may be wound on the upper surface S1, the outer circumferential surface S2, the lower surface S3, and the inner circumferential surface S4 of the ferrite core 110 having a ring shape. A bobbin (not shown) for insulating the ferrite core 110 from the coil 120 may be further disposed between the ferrite core 110 and the coil 120. The coil 120 may be formed as a wire having an insulating material coated on a surface thereof. The wire may be formed of copper, silver, aluminum, gold, nickel, tin, etc., whose surface is coated with an insulating material, and the cross section of the wire may have a circular or square shape.

The coil component according to the embodiment of the present invention may be variously applied to, for example, an inductor, a choke coil, a transformer, a motor, a Direct Current (DC)/DC transformer, and an electromagnetic interference (EMI) shield case, but is not limited thereto, and may be variously applied to vehicles and industrial applications.

In this case, a coil component is shown in which a pair of coils are symmetrically wound around a ferrite core having a ring shape, but is not limited thereto.

The ferrite core according to the embodiment of the present invention may be applied to coil components having various shapes around which a coil is wound.

The ferrite core 110 according to an embodiment of the present invention may be an Mn-Zn type ferrite core containing Mn, Zn and Fe.

Fig. 2 is an enlarged view illustrating a portion of a ferrite core according to an embodiment of the present invention, fig. 3 is an image of the ferrite core according to an embodiment of the present invention taken by an optical microscope, fig. 4 is a content distribution diagram of some additives in the ferrite core according to an embodiment of the present invention in an area a of fig. 3, and fig. 5 is a content distribution diagram of the remaining additives in the ferrite core according to an embodiment of the present invention in an area B of fig. 3.

Referring to fig. 2 and 3, the ferrite core 110 according to an embodiment of the present invention includes crystal grains 200 containing Mn, Zn, and Fe, and grain boundaries 210 located between the crystal grains. In this case, the crystal grain 200 may include Mn of 30 to 40 mol%, preferably 33 to 39 mol%, more preferably 35 to 38 mol%, based on the total content of Mn, Zn, and Fe; 5 to 15 mol%, preferably 7 to 13 mol%, more preferably 9 to 11 mol% Zn; and 50 to 60 mol%, preferably 51 to 57 mol%, more preferably 52 to 54 mol% Fe.

In addition, the ferrite core 110 according to an embodiment of the present invention may further include Co, Ni, SiO₂CaO and Ta₂O₅. In addition, the ferrite core 110 according to an embodiment of the present invention may further include Nb₂O₅And V₂O₅。

In the ferrite core 110 according to an embodiment of the present invention, the composition of the crystal grains 200 may be different from the composition of the grain boundaries 210. In particular, Co, Ni, SiO in the crystal grain 200₂CaO and Ta₂O₅May be contained in the same amount as Co, Ni, SiO in the grain boundary 210₂CaO and Ta₂O₅The content of at least one of them is different. Further, Nb in the crystal grain 200₂O₅And V₂O₅May be present in an amount corresponding to the amount of Nb in the grain boundary 210₂O₅And V₂O₅The content of at least one of them is different. In this specification, Co, Ni, SiO₂、CaO、Ta₂O₅、Nb₂O₅And V₂O₅Are described as being present in grains 200 and/or grain boundaries 210, but may be described as being present therein in the form of Co, Ni, Si, Ca, Ta, Nb, and V, respectively.

Referring to fig. 4 and 5, Co and Ni may be distributed in the grains 200 at a higher content than in the grain boundaries 210 located between the grains 200, and SiO₂CaO and Ta₂O₅May be distributed in the grain boundary 210 between the grains at a higher content than in the grains 200. Further, Nb₂O₅And V₂O₅It may also be distributed in the grain boundary 210 between the grains at a higher content than in the grains 200. For example, Co and Ni may be distributed in the grains at a content twice or more of that in the grain boundary 210 between the grains 200200, and SiO₂CaO and Ta₂O₅It may be distributed in the grain boundary 210 located between the grains at a content twice or more as large as that in the grains 200. Further, Nb₂O₅And V₂O₅It may be distributed in the grain boundary 210 between the grains at a content twice or more as large as that in the grains 200. In this case, the content may refer to at least one of weight ratio, volume ratio, mole ratio, and parts per million (ppm).

In this case, Co is in the crystal grain 200²⁺Can be made of Fe²⁺And (4) replacement. Therefore, the content of Co in the crystal grains 200 may be higher than that in the grain boundaries 210, the temperature dependence of the permeability of the ferrite core 110 may be improved due to the content, and the magnetic anisotropy may be controlled by the content.

Further, since Ni in the crystal grains 200 replaces Zn of the ferrite core 110, the content of Ni in the crystal grains 200 may be higher than that in the grain boundary 210, and Fe₂O₃The content of (a) is relatively increased due to Ni. Therefore, the minimum temperature at which core loss starts to occur can be increased.

Next, SiO₂Magnetic properties can be improved, move across the grain boundaries 210, and induce growth of the grains 200. However, SiO may be contained in the crystal grain 200 in an amount of 1ppm to 200ppm, preferably 50ppm to 150ppm₂. When SiO is contained in it in an amount of 200ppm or more₂In this case, the crystal grains 200 may be excessively grown, so that the average grain size of the crystal grains 200 may become excessively large, and the interval between the crystal grains, i.e., the length of the grain boundary 210 between the crystal grains 200 may become large. Therefore, the strength of the ferrite core may be weakened, the permeability thereof may be reduced, and the loss thereof may be increased.

In turn, CaO may improve the high frequency response of the ferrite core 110. In addition, since CaO exists in the grain boundary 210, CaO serves to reduce the hysteresis loss thereof.

Next, V₂O₅A liquid film is formed on the grain boundary 210 for suppressing the growth of the crystal grain 200, so that the eddy current loss thereof can be reduced.

Then, when Ta₂O₅Ta when present in the grain boundary 210₂O₅The resistance of the grain boundary can be increased and used to suppress the overgrowth of the crystal grains 200.

In addition, when SiO is added₂When used together with CaO, CaO precipitates in the grain boundary 210 to increase the resistance of the grain boundary 210, thereby serving to suppress the excessive growth of the crystal grains 200.

As described above, V₂O₅、Ta₂O₅And SiO₂The + CaO serves to suppress the excessive growth of the crystal grains 200, and as a result, the eddy current loss can be reduced.

In addition, SiO is incorporated therein₂And CaO and Ta₂O₅In the case of use together, Ta₂O₅Helps the CaO to be uniformly distributed in the grain boundary 210, so that the hysteresis loss can be reduced. In this case, Ta₂O₅Can use Nb₂O₅Or ZrO₂Instead of, and Nb₂O₅Or ZrO₂May also exert a reaction with Ta₂O₅The same function, and hysteresis loss of the ferrite core 110 can be reduced.

As described above, in the case of CaO, V for controlling grain growth₂O₅、Ta₂O₅And SiO₂In the case where the crystal grains are distributed in the grain boundary at a higher content than the content in the crystal grains, the excessive growth of the crystal grains can be suppressed, the particle diameter of the crystal grains can be controlled, the grain boundary, that is, the interval between the crystal grains can be reduced, and the eddy current loss and the hysteresis loss can be reduced.

With further reference to fig. 2 and 3, the average spacing between the grains 200 in the ferrite core 110, i.e., the average spacing D between the grains 200, may be in the range of 0.5 μm to 3 μm and preferably in the range of 1 μm to 2 μm, and the average particle diameter D of the grains 200 may be in the range of 3 μm to 16 μm and preferably in the range of 7 μm to 12 μm. In the case where the average spacing D between the crystal grains 200 and the average particle diameter D of the crystal grains 200 satisfy the above value ranges, a ferrite core high in magnetic permeability, low in core loss, and excellent in formability, machinability, and strength, thereby being high in reliability, can be obtained.

In the present specification, the interval between crystal grains may be used together with the distance between crystal grains, the grain boundary, the distance of the grain boundary, the diameter of the grain boundary, the interval of the grain boundary, and the like.

Fig. 6 is a flowchart illustrating a method of manufacturing a ferrite core according to an embodiment of the present invention.

Referring to fig. 6, the raw material, CoO and NiO are mixed (S600). In this case, the raw material may contain Fe with a purity of 99% or more₂O₃、Mn₃O₄And ZnO, and the raw material, CoO, and NiO may be mixed using a ball mill at 20rpm to 30rpm and preferably at about 24rpm for 12 hours to 24 hours and preferably for about 18 hours. In this case, CoO may be added thereto at 1500ppm to 5500ppm, preferably 2500ppm to 3500ppm, more preferably 3000ppm to 4000ppm, and NiO may be added thereto at 300ppm to 500ppm, more preferably 350ppm to 450 ppm.

Next, the mixed raw material, CoO, and NiO are subjected to a calcination process (S602). In this case, the mixed raw material, CoO and NiO may be treated at a temperature rising rate of about 3.33 ℃/minute for 4 to 6 hours, preferably about 5 hours, so that the maximum temperature thereof is 900 to 1000 ℃, preferably about 950 ℃. The densities of the raw materials, CoO and NiO mixed by the calcination process can be improved.

Next, a slurry is manufactured (S604). For this, the powder subjected to the calcination process may be mixed with a solvent, a binder, and a dispersant and stirred for 10 hours or more. In this case, the solvent may be distilled water, and the binder may be polyvinyl alcohol. The powder may comprise about 1 wt% binder and about 0.1 wt% to 0.3 wt% dispersant.

Next, a spray drying process is performed (S606). For this, the slurry may be continuously fed into the chamber, and the spray drying process may be performed using a rotary atomizer and a spray dryer. In this case, the inlet temperature of the chamber may be about 160 ℃ and the outlet temperature may be about 100 ℃, when the diameter of the chamber is about 1500mm, the slurry may be injected into the chamber at a rate of 12 kg/hour, and the speed of the rotary atomizer may be set to about 7000 rpm. When the spray drying process is performed, the particles may be granulated into a spherical shape.

Next, additional additives are mixed (S608). In this case, the further additive may comprise SiO₂CaO and Ta₂O₅. In addition, the additional additive may further comprise Nb₂O₅And V₂O₅. In this case, SiO may be added in an amount of 1ppm to 200ppm, preferably 50ppm to 150ppm₂400 to 600ppm, preferably 450 to 550ppm CaO may be added, and 400 to 600ppm, preferably 450 to 550ppm Ta may be added₂O₅. Furthermore, from 250ppm to 450ppm, preferably from 300ppm to 400ppm, of Nb may be added₂O₅And V may be added in an amount of 400ppm to 600ppm, preferably 450ppm to 550ppm₂O₅。

Next, the magnetic core is shaped and sintered (S610). For this purpose, the magnetic core may be formed with a pressure of 4 to 5 tons per unit area and at a temperature of 1360 ℃ at maximum for 6 hours.

Next, a surface polishing process or the like may be further performed.

In the case of manufacturing a ferrite core by such a process, since the contents of CoO and NiO in crystal grains can be high and CaO, V in grain boundaries can be high₂O₅、Ta₂O₅And SiO₂Can be high, so that a ferrite core can be obtained which enables control of the diameter of crystal grains and the distance between the crystal grains and which has high strength, high permeability and low loss.

Hereinafter, a more detailed description will be given with reference to examples and comparative examples.

In order to manufacture the ferrite cores according to the examples and comparative examples, Mn, Zn, and Fe were added as raw materials at 36.3 mol%, 10 mol%, and 53.5 mol%, respectively, the amounts of additional additives were adjusted according to the following table 1, and the manufacturing method of fig. 6 was performed.

[ Table 1]

Table 2 shows the measurement results of the permeability and the core loss of each of the ferrite cores according to the embodiment and the comparative example, and table 3 shows the measurement results of the strength of each of the ferrite cores of the embodiment 3 and the comparative example 1, and fig. 7 is a set of images of the ferrite cores of the embodiment 3, the embodiment 4, the comparative example 1, and the comparative example 2 taken by an optical microscope.

[ Table 2]

[ Table 3]

Experiment number	Strength (N)
		Example 3	910
Comparative example 1	750

Referring to tables 1 and 2, according to the embodiments of the present invention, an Mn — Zn based ferrite core having a permeability of 3000 or more and a loss of 800 or less can be obtained. In particular, Nb was further added as in example 3₂O₅And V₂O₅In the case of the additive, the loss can be reduced to 500 or less.

Referring to tables 1 and 3, the strength was measured using a Universal Testing Machine (UTM) under the conditions of a maximum load of 970N and a speed of 30 mm/min, and it can be seen that the strength of example 3 is greater than that of comparative example 1.

Further, referring to fig. 7, it can be seen that the grain boundaries, i.e., the intervals between the crystal grains, in each of example 3 and example 4 are smaller than the intervals between the crystal grains in each of comparative example 1 and comparative example 2. That is, SiO was mixed as in examples 3 and 4₂In the case where the content of (b) is limited to 1ppm to 200ppm, excessive growth of crystal grains can be prevented, so that the average grain diameter of the crystal grains can be controlled to a level in the range of 3 μm to 16 μm, and the average spacing between the crystal grains can be reduced to a level in the range of 0.5 μm to 3 μm, whereby higher permeability and lower core loss can be obtained. In particular, in the formation of SiO₂With the content of (b) being limited to 50ppm to 150ppm, the average spacing between crystal grains can be further reduced, and thus, it can be seen that the core loss is further reduced.

While the present invention has been described with reference to the exemplary embodiments thereof, it will be understood by those skilled in the art that various changes may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.