JPH0532975B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise filter and a magnetic core for an inductor used therein. More specifically, the present invention relates to a noise filter used as a power line filter that is inserted into a power line to remove common mode and normal mode noise, and an inductor magnetic core used therein. Prior art and its problems In general, when removing noise, there are two components: symmetrical noise components between signal lines (normal mode) and asymmetrical noise components between signal lines and ground (common mode).
It is necessary to consider both. A conventional noise filter is configured to remove noise by inserting a capacitor with a large capacitance between a signal line and ground, and by inserting an inductor in series with the signal line. FIG. 1 shows an example of such a conventional noise filter. In FIG. 1, 1 and 2 are inductors, 3 and 4 are capacitors that short-circuit noise to ground, and 5 is a capacitor that has an effect only on symmetrical noise components. The capacitance of the capacitor generally used is 0.1 μF to 5 μF. By the way, if the configuration is as shown in Figure 1, 100V
Alternatively, if it is inserted into a 200V power line and used as a power line filter, a leakage current of several mA to several tens of mA will flow, causing the inconvenience of exceeding safety standards in Europe, America, and Japan. Furthermore, if the grounding is insufficient, there may be disadvantages such as feeling an electric shock when touching the filter. In order to prevent such defects, the signal line -
A possible solution would be to reduce the capacitance of the capacitor between the ground and bring it within safety standards. However, in this case, the attenuation effect as a noise filter deteriorates. Therefore, in order to improve the attenuation effect, it is necessary to increase the inductance of the inductors 1 and 2 and to prevent saturation with the power supply current. However,
Attempts to satisfy such requirements would result in drawbacks such as the dimensions of the inductors 1 and 2 becoming extremely large and the cost significantly increasing. In view of these circumstances, the applicant of this application:
As an earlier application of this application, we proposed a common mode chiyoke coil in which a magnetic core is provided with reciprocating windings so that the magnetic flux cancels each other, a capacitor, and a magnetic core connected in series with each winding of the common mode chiyoke coil. proposed a noise filter with an inductor formed by winding.
Publication No. 56829). An example of such a noise filter is shown in FIG. In FIG. 2, reference numeral 8 denotes a chiyoke coil using a magnetic core of high magnetic permeability such as ferrite or amorphous magnetic alloy, and is provided with reciprocating windings so that the magnetic fluxes cancel each other out. The inductance per wire is approximately 1 to 10 mH. Further, numerals 9 and 10 are capacitors for asymmetric components, and the capacitance is about 0.01 to 0.001 μF. moreover,
Reference numeral 11 denotes a capacitor for covering the insufficient attenuation of the symmetrical component. Inductors 6 and 7 are connected in series to each winding of the common mode York coil. This inductor has a magnetic core made of a material with a high saturation magnetic flux density, such as an amorphous magnetic alloy or a silicon steel plate. According to the noise filter having such a configuration, even if the capacitance of the capacitors 9 and 10 between the signal line and the ground is made small, a sufficient attenuation effect can be obtained for the symmetric noise component. Therefore, it is possible to suppress leakage current so as to satisfy safety standards in Europe, America, and Japan. In addition, since the magnetic core used in the common mode choke coil is configured so that the power supply current is canceled by the reciprocating line, it is possible to use a magnetic core that easily saturates, such as a ferrite magnetic core. It can be manufactured much cheaper than increasing the inductance by 1 or 2, and it is possible to reduce the cost. By the way, if a winding of a normal amorphous magnetic alloy is used as the magnetic core of the inductors 6 and 7 in the noise filter having such a structure,
The drawback is that the frequency band width of the noise that can be removed with an attenuation rate above a certain level (40 dB or higher) is narrow. In addition, the amount of noise attenuation per unit volume of the magnetic core is small, and a smaller magnetic core is required. Furthermore, there is also the disadvantage that these characteristics deteriorate over time due to repeated operations and storage over a long period of time. The present inventors have previously proposed that microcrystals be partially precipitated in an amorphous magnetic alloy to thereby improve magnetic properties, and such a material is used. Although the above characteristics are improved, they are still insufficient. Purpose of the Invention The present invention was made in view of the above-mentioned circumstances, and its main purpose is to improve the common mode choke coil, capacitor, and each winding of the common mode choke coil in the above-mentioned previous proposal. In a noise filter consisting of an inductor having an amorphous magnetic alloy core connected in series, the frequency band of the noise to be removed is widened at a certain attenuation rate or higher, and the amount of noise attenuation per unit volume of the inductor itself is increased. , which aims to reduce deterioration of the inductor over time. Such objects are achieved by the present invention as described below. In other words, the present invention comprises a common mode chiyoke coil in which a magnetic core is provided with reciprocating windings so that magnetic fluxes cancel each other out, and a pair of capacitors each connected between each winding of the common mode chiyoke coil and the ground. , a noise filter having a pair of inductors connected in series to each winding of the common mode choke coil, wherein the inductor is wound around a magnetic core made of a wound body of an amorphous magnetic alloy thin plate. The noise filter is characterized in that the amorphous magnetic alloy thin plate partially contains crystalline material and has a composition represented by the following formula. Formula Fe _x Mn _y (Si _p B _{q Pr} C _s ) _z {In the above formula, x+y+z=100 at%, of which y is 0.01 to 10 at% and z is 21 to 25.5 at%. p+q+r+s=100at%, of which,
p is 40-75at%, r is 0.01-5at%, s/q is 0.03
or more and less than 0.05. Further, z≦0.5p+1, z≦0.1p+19, z≧0.3p+2, and z≧0.13p+13.7. } Further, the second invention partially contains crystalline material,
A magnetic core for an inductor is characterized in that it is constituted by a wound body formed by winding a thin ribbon of an amorphous magnetic alloy having a composition represented by the above formula. Specific Configuration of the Invention The specific configuration of the present invention will be described in detail below. The thin plates of amorphous magnetic alloy used for the magnetic cores of the inductors 6 and 7 of the noise filter of the present invention partially contain crystalline materials. In the thin plate, the crystalline material partially contained in the amorphous material is generally precipitated microcrystals and mixed in the amorphous material. Therefore, when X-ray analysis of a thin plate is performed, the diffraction spectrum shows a pattern in which a peak indicating the presence of crystalline material is superimposed on a halo characteristic of amorphous material, and the diffraction image shows a pattern in which peaks indicating the presence of crystalline material are superimposed on a halo peculiar to amorphous material. A spot is superimposed on the surface, and a Debye Scherer ring with a predetermined return diameter and width appears. Then, by taking the area ratio between the halo and the peak of the diffraction spectrum, the abundance ratio of crystalline and amorphous in the ribbon can be determined. is usually preferably about 0.1 to 50%. Further, the precipitated microcrystals are generally considered to have an average grain size of approximately 10 to 1000 angstroms, based on the ring diameter and ring width of the Debye-Schierer ring. When an inductor magnetic core is formed from a thin plate using such partially existing microcrystals,
The noise band to be removed becomes wider, the amount of attenuation per unit volume increases, and deterioration over time decreases. Next, to explain the composition of the amorphous magnetic alloy, the Mn content y is 0.01 to 10 at%, preferably 0.1 to 5 at%. If it is less than 0.01%, deterioration over time is large. In addition, the crystallization temperature is low, and the temperature and time required for heat treatment for precipitation of microcrystals, which will be described later, are severely restricted, making it difficult to partially contain crystalline materials as described above. On the other hand, when y exceeds 10 at%, deterioration over time becomes large and it becomes difficult to produce a thin plate. In addition, saturation magnetization is reduced and the noise attenuation rate is also reduced. On the other hand, the content z of the vitrifying elements consisting of Si, B, P and C is 21.0 to 25.5 at%. When z exceeds 25.5at%, the saturation magnetization decreases,
Since a large magnetic core volume is required, the winding becomes large, copper loss increases, and heat generation increases. On the other hand, when z is less than 21.0 at%, it becomes difficult to make the sheet thinner, the structural yield becomes poor, and the surface properties of the thin sheet deteriorate. In addition, the crystallization temperature decreases,
The temperature and time required for heat treatment for precipitation of microcrystals are severely restricted, making it difficult to partially contain crystalline materials as described above. Furthermore, corrosion resistance deteriorates and durability also deteriorates. The thin plate in the present invention is 0.01~
Contains 10 at% Mn and 21.0 to 25.5 at% vitrifying elements containing Si, B, P and C, the balance being:
64.5-78.9at%, more preferably 69.5-78.9at%
Consisting of Fe. In this case, the vitrification element is p+q+r+s=
Under the condition of 100at%, pat% Si and qat% B,
It consists of rat% P and sat% C. The silicon content ratio p in the vitrification element is 40~
It is 70at%. If p is less than 40 at%, magnetic properties such as magnetic permeability will deteriorate, and deterioration over time will be large. On the other hand, if it is greater than 75 at%, the magnetic properties are unsatisfactory. In addition, the total content of vitrification elements zat%,
The following relationships must be satisfied between the Si content ratio pat% in the vitrification element: z≦0.5p+1, z≦0.1p+19, z≦0.3p+2, and z≦0.13p+13.7. That is, if we explain these conditions based on Figure 3, when expressed in coordinates (z, p),
Point A (40, 21.0), B (45, 23.5), C (65, 25.5),
D (75, 25.5), E (75, 24.5), F (70, 23.0), G
(55, 21.0) and A are sequentially connected by straight lines, and the area surrounded by these straight lines is the condition where z and p of the thin plate in the present invention are satisfied. Only within this region, the volume of the magnetic core at which a predetermined noise attenuation rate can be obtained becomes small. In addition, above the C-D line (z=25.5) and G
- The disadvantages below line A (z=21.0) are as described above, but below line A-B (z=21.0) shown in the figure
0.5p+1) and above the B-C line (z=0.1p+19), the magnetic core volume at which a predetermined noise attenuation rate can be obtained increases, the magnetic properties are poor, and deterioration over time is large. Also, the E-F line (z=0.3p+2) and the F-G line
Below the line (z = 0.13p + 13.7), there is a drawback that it becomes difficult to obtain an amorphous thin plate using the high-speed quenching method. Furthermore, the heat treatment conditions for precipitation of microcrystals are severe, making it difficult to cause crystalline particles to partially exist. On the other hand, the phosphorus P content ratio rat% in the vitrification elements is
It is 0.01 to 5 at%, more preferably 0.01 to 2 at%. If it is less than 0.01 at%, deterioration over time will increase, and if it is more than 5 at%, the amount of heat generated will increase. Further, the value obtained by dividing the carbon C content ratio s in the vitrification element by the boric acid B content ratio q is 0.03 to 0.05. Only when the value is greater than 0.03, the change over time becomes sufficiently small, and a change over time equivalent to 0.05 to 0.4 can be obtained. In addition, in the above-mentioned composition, other transition metal elements other than Fe and Mn (Sc~Zn, Y~
Cd, La~Hg, Ac~) may be included.
Preferred specific examples include Co, Ni,
Examples include one or more of Cr, Cu, Mo, Nb, Ti, W, V, Zr, Ta, Y, and rare earth elements. However, these contents are usually 10at% of Fe,
In particular, it is less than 5at%. On the other hand, elements other than Si, B, P, and C may be included as vitrifying elements. Preferred specific examples include one or more of A1, Be, Ge, Sb, In, and the like. However, the content ratio of vitrification elements, Si, B,
Usually 10at% or less, especially 5% of the total of P and C
It is as follows. The thin plate in the present invention is not particularly limited as long as it satisfies the conditions detailed above. However, as a result of partially introducing crystalline material into the thin plate, especially when magnetic anisotropy is imparted in a predetermined direction within the plane of the thin plate, the noise band to be removed becomes wider, the amount of attenuation increases, and This is preferable in that various magnetic properties can be easily adjusted. In this case, the magnetic anisotropy is preferably introduced in one predetermined direction within the plane of the thin plate, usually as uniaxial anisotropy. That is, when a thin plate of an almost completely amorphous magnetic alloy is heat-treated in a non-magnetic field before the winding described below, or in some cases after the winding, microcrystals are precipitated. Uniaxial anisotropy is imparted to the longitudinal direction of the thin plate, and at this time, the noise bandwidth that can be removed with an attenuation rate of 40 dB or more becomes extremely wide. In addition, if microcrystals are precipitated by heat treatment by applying a magnetic field before or after winding the thin plate in a direction that makes a predetermined angle with the longitudinal direction of the thin plate, is given uniaxial anisotropy, and by setting the anisotropy direction to a predetermined direction, the squareness ratio and the unsaturated region of the B-H loop can be adjusted as desired, and the DC superposition Characteristics are improved. The existence of such magnetic anisotropy is explained by the conventional method,
This can be easily verified by measuring the torque curve. Such a thin plate has a thickness of about 10 to 100 μm and a width of about 0.1 to 50 cm, and is usually a long thin plate. The inductor magnetic core in the present invention is usually constructed from a wound body formed by winding such a thin plate. That is, the magnetic core may be formed from the wound body itself formed by winding a thin plate. Also, cut the rolled body to make U-shape, C-shape, I-shape, L-shape
It is also possible to form a cut body into a shape such as a letter, use this cut body as a cut core, and then butt the cut cores against each other to form a magnetic core. In this way, when the magnetic core is formed into a cut core shape, the winding work becomes easier. The inductor magnetic core in the present invention is composed of a wound body of thin plates, and is not made by laminating thin plates into a predetermined shape. This is due to the following reasons. That is, as described above, preferable results can be obtained when the thin plate is given uniaxial magnetic anisotropy in a predetermined direction within the plane of the thin plate due to the precipitation of microcrystals. The treatment for precipitation of such microcrystals is usually carried out before forming the wound body, and then the wound body is obtained from this, but the direction of the easy axis in the resulting wound body is Since it is constant with respect to the direction of the magnetic path, high characteristics such as the amount of heat generated can be obtained. On the other hand, when creating a laminated structure, thin plates with a predetermined in-plane anisotropy are etched or punched and then laminated, so the directions of the magnetic path and easy axis are not constant. First, high properties such as calorific value cannot be obtained. Furthermore, even when performing a treatment for precipitating microcrystals after winding, an easy axis having a desired arbitrary constant angle can be easily introduced into the magnetic path. On the other hand, with the laminated type, the angle between the two cannot be set to an arbitrary value at a constant angle in the magnetic path.
Even if it were possible, it would be extremely difficult. In addition, the inductor magnetic core of the present invention can be used not only when it is made of a wound body itself, but also when it has various cut core shapes as described above, and even when it has a gap as described later, the easy axis is aligned with the magnetic path direction. The angle formed is always constant and can be any angle. Incidentally, since the wound body is better in terms of characteristic deterioration during core processing, the structure made of the wound body in this manner facilitates manufacturing and reduces manufacturing costs. When constructing a magnetic core from a wound body in this manner, the wound body is formed by winding a thin plate around a predetermined winding frame, winding core, etc., and fixing the ends thereof. In this case, the reel,
The structure, shape, etc. of the winding core etc. may be various. In addition, the material may be magnetic, glass, resin, etc., or metal, and the end portion may be fixed by adhesive, welding, tape, etc., or by being provided on a winding frame, etc. It may also be caulked with a caulking nail. Note that an insulating material may be interposed between the wound thin plates. Moreover, unlike the above, the shape can also be fixed by impregnating it with a resin or the like, for example, without using a winding frame or a winding core. In addition, the winding shape can be changed in various ways, such as a circular ring shape or a square ring shape. On the other hand, in order to cut such a wound body to obtain a cut body and make it into a cut core in an I-shape, C-shape, etc., it is necessary to impregnate the cut part of the wound body with resin, etc. You can fix it in place or fix it with caulking nails, etc., and then cut it. From these various cut cores, U-U, C-C, L-L, C-I
Magnetic cores with various cut core shapes are constructed. Furthermore, a gap is formed in a portion of the magnetic path of such a magnetic core. This is because the presence of the gap widens the unsaturated region of the B-H loop and improves the DC superposition characteristics. In this way, to provide a gap in a part of the magnetic path, the cut portion may be fixed and the wound body may be cut with a predetermined gap width, as in the case of forming the above-mentioned cut body, or the wound body may be cut with a predetermined gap width. A predetermined gap may be provided when the cut cores are brought together. The gap width is usually 0.001 to 0.001 of the magnetic path length.
It should be about 0.05. Further, various insulating materials such as insulating paper, resin such as polyethylene terephthalate (PET), etc. may be loaded into the gap. The inductor magnetic core of the present invention is usually manufactured as follows. First, an almost completely amorphous thin plate is obtained from a master alloy having a corresponding composition according to a known high-speed quenching method. This thin plate is then usually subjected to a treatment for precipitation of microcrystals. Such treatment is usually carried out in the absence of a magnetic field by heating at a temperature near the crystallization temperature for a suitable period of time, followed by cooling, for example air cooling. Superheating temperature, superheating time, cooling rate, etc. can be easily determined experimentally depending on the required characteristic values. The atmosphere for such heat treatment may be air, vacuum, inert gas, non-oxidizing gas, or the like. Alternatively, the heat treatment as described above can also be performed in a static magnetic field. In this case, the applied magnetic field is, for example, about 1000e. And at this time,
Anisotropy that forms a predetermined angle with the longitudinal direction within the ribbon surface is imparted. Further, the heat treatment can be performed while applying tension, or even in a rotating magnetic field depending on the case. Next, as described above, this thin plate is wound to obtain a wound body, and various cut cores are formed from this, and they are brought together through gaps to form a magnetic core, or a predetermined gap is provided in the wound body to form a main body. An inventive inductor core is formed. Note that the thin plate may not be subjected to the treatment for precipitating microcrystals in advance, but the treatment may be performed either after producing the wound body, after forming the cut core, or after forming the gap. Further, when a thin plate is previously subjected to a treatment for precipitation of microcrystals and then a wound body is obtained, heat treatment may be separately applied to remove strain after the winding body is manufactured. Then, a predetermined winding is applied to the magnetic core as described above, and other predetermined processing is performed to form an inductor. Note that L of such an inductor is 10 μH ~
It is said to be about 1mH. As described above, the inductors 6 and 7 are each connected to each winding of the common mode choke coil 8, and are combined with the capacitors 9, 10, and 11 to form a noise filter. Specific Effects of the Invention Since the noise filter of the present invention uses an inductor with a magnetic core made of a predetermined amorphous magnetic alloy, the frequency band width of noise that is removed at a certain attenuation rate (for example, 40 dB or more) is Significantly wider bandwidth. Further, the amount of noise attenuation is significantly improved compared to when a magnetic core of the same size is formed using other amorphous magnetic alloys. Furthermore, even after long-term use or long-term storage,
Deterioration over time of the frequency band width of removed noise and the amount of noise attenuation is significantly reduced. Furthermore, since the heat treatment conditions for precipitation of microcrystals are easy, the magnetic core can be manufactured easily. Furthermore, it has high corrosion resistance. As a result, the advantages of the previous proposal, such as being able to reduce the capacitance of the capacitors 9 and 10, can be fully utilized. Such an effect is caused by s/q in the above equation
Equivalent to 0.05 to 0.4. Specific Examples and Comparative Examples of the Invention Next, Examples and Comparative Examples of the present invention will be shown to explain the present invention in further detail. Example 1 Five types of amorphous magnetic alloy thin plates having different compositions shown in Table 1 below but having different s/q but other compositions included in the above formula were obtained. They are almost completely amorphous and both have a thickness of
It is 30μm.

[Table] Using these five types of thin plates, the inner diameter is 15 mm, the outer diameter is 27 mm,
A toroidal wound band with a width of 10 mm was obtained. For these five types of wound bodies A-1 to A-5,
After heat treatment at 400℃ for 30 minutes, the wound body was impregnated with epoxy resin, the resin was cured, and then the wound body was cut to form a gap with a width of 1 mm in the magnetic path. Insert PET and inductor magnetic core A
-1 to A-5 were obtained. X-ray diffraction revealed halos and peaks in the thin plates of each of the magnetic cores A-1 to A-5. Inductor magnetic cores A-1 to A-A thus obtained
-5, a wire was wound so that L=200 μH, and this was incorporated into the noise filter shown in FIG. In this case, L of the common mode choke coil 8
is 2.5mH, capacitors 9 and 10 are 4700pF, and capacitor 11 is 0.22μF. Using such a noise filter, the attenuation rate (dB) at f=150kHz was measured at a rating of 15A. The results are shown in Table 2. Furthermore, each of these inductors was stored in a constant temperature bath at 120° C. for 1000 hours, and then the noise filter was manufactured and the change in the attenuation rate over time was measured. The results are also listed in Table 2. In the table, × indicates that there was a large change, △ indicates that there was a change, and 〇 indicates that there was no change.

[Table] From the results in Table 2, it can be seen that when s/q is 0.03 to 0.4, the attenuation rate becomes 40 dB or more, and deterioration over time decreases. Also, 40dB at s/q=0.03~0.4
The noise bandwidth that could be removed with the above attenuation rate was also extremely large. In other words, even if the value is 0.03 or more and less than 0.05, the
This shows the same effect as s/q=0.05 to 0.4 in Publication No. 193005. In addition, it was confirmed that inductor A-5 using a thin plate with s/q≧0.4 generates a lot of heat and is not suitable as inductors 6 and 7. Comparative Example 1 A similar experiment was conducted using the composition of Fe ₇₄ Si ₁₃ B ₁₃ .

【table】 The results are shown in Table 4.

[Table] Example 2 In the above formula, Mn content y is 0.5 at%, P content ratio r in the vitrification element component is 0.1 at%, C and B
The content ratio s/q of Si in the vitrification element component is fixed to 0.037, and
Various thin plates were produced by changing the content ratio p. Next, each thin plate was cut into 15 mm inner diameter, 27 mm outer diameter, and 10 mm width.
After winding into a toroidal shape, each winding body is heated to 440℃,
Heat treatment was performed in a non-magnetic field for 40 minutes, impregnated with epoxy resin, fixed, and a gap of 1 mm was provided in the magnetic path to obtain various magnetic cores. As a result of the heat treatment performed in this manner, a halo and a peak were present in the X-ray diffraction spectrum of each thin plate. Next, for each magnetic core obtained in this way, an inductor and a noise filter were manufactured in the same manner as in Example 1, and the attenuation rate at f = 150kHz at a rating of 15A was measured.A-B-C -D-E-F-
Inductors obtained from thin plates with compositions within the region surrounded by G-A had attenuation rates greater than 40 dB, while outside this range the attenuation was less than 40 dB. In addition, when we measured changes over time for various inductors, all inductors obtained from thin plates with compositions in the area surrounded by A-B-C-D-E-F-G-A were the same as in Example 1. It showed excellent characteristics equivalent to those of inductors A-2 to A-4. Furthermore, each composition was heat-treated for 40 minutes.
The heat treatment temperature width ΔTan of the heat treatment temperature Tan to obtain good characteristics in terms of the attenuation rate and change over time was determined. As a result, the thin plate having the composition within the region surrounded by A-B-C-D-E-F-G-A exhibited a heat treatment temperature width ΔTan of 20° C. or more. Note that all thin plates having compositions within the region surrounded by A-B-C-D-E-F-G-A exhibited excellent corrosion resistance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional noise filter. FIG. 2 is a circuit diagram showing the noise filter of the present invention. Figure 3 shows the composition of the amorphous magnetic alloy thin plate used for the inductor core of the noise filter of the present invention, particularly the Si content ratio p in the vitrification element component.
(%) and the amount of vitrification element component z (at%).

Claims (1)

[Claims] 1. A common mode chiyoke coil formed by winding a reciprocating winding around a magnetic core so that magnetic fluxes cancel each other out, and a pair of windings connected between each winding of this common mode chiyoke coil and the ground. A noise filter having a capacitor and a pair of inductors connected in series to each winding of the common mode choke coil, wherein the inductor is wound around a magnetic core made of a wound body of an amorphous magnetic alloy thin plate. A noise filter, characterized in that the amorphous magnetic alloy thin plate partially contains crystalline material and has a composition represented by the following formula. Formula Fe _x Mn _y (Si _p B _{q Pr} C _s ) _z {In the above formula, x+y+z=100 at%, of which y is 0.01 to 10 at% and z is 21 to 25.5 at%. p+q+r+s=100at%, of which,
p is 40 to 75 at%, r is 0.01 to 5 at%, s/q is 0.03
or more and less than 0.05. Further, z≦0.5p+1, z≦0.1p+19, z≧0.3p+2, and z≧0.13p+13.7. } 2. The noise filter according to claim 1, wherein the magnetic core of the inductor is made of a wound body of the amorphous magnetic alloy thin plate, and has a gap in a part of the magnetic path. 3. The noise filter according to claim 1, wherein the magnetic core of the inductor is formed by connecting cut cores obtained by cutting the wound body of the amorphous magnetic alloy thin plate through a gap. 4. A magnetic core for an inductor, comprising a wound body formed by winding a ribbon of an amorphous magnetic alloy that partially contains crystals and has a composition represented by the following formula. Formula Fe _x Mn _y (Si _p B _{q Pr} C _s ) _z {In the above formula, x+y+z=100 at%, of which y is 0.01 to 10 at% and z is 21 to 25.5 at%. p+q+r+s=100%, of which p
is 40 to 75 at%, r is 0.01 to 5 at%, and s/q is 0.03 or more and less than 0.05. Further, z≦0.5p+1, z≦0.1p+19, z≧0.3p+2, and z≧0.13p+13.7. }