JP5515195B2 - Ni-Zn ferrite powder, green sheet containing the Ni-Zn ferrite powder, and Ni-Zn ferrite sintered body. - Google Patents

Description

  The present invention relates to a Ni—Zn-based ferrite material, and more specifically, provides a Ni—Zn-based ferrite material having excellent direct current superposition characteristics by adding silicon oxide.

  In recent years, electronic devices such as portable devices and information devices have been required to be rapidly downsized and highly functional, and components such as inductance elements used in these devices are also required to be downsized and highly functional. Has been. In particular, an inductance element used in a power supply circuit is required to have as little inductance reduction as possible even when a large DC current is passed as a DC superposition characteristic. Further, since an alternating current flows through the inductance element, it is also necessary that the permeability is high at the frequency used and the core loss is small.

  Conventionally, an inductance element uses Mn—Zn ferrite or Ni—Zn ferrite as a material, and structurally provides a magnetic gap to improve DC superposition characteristics and adjust the ferrite composition. The core loss was reduced by adding additives.

  In particular, in the case of a multilayer inductance element, since it is manufactured by laminating a ferrite material and a nonmagnetic material that is a magnetic gap and firing simultaneously, due to the adhesion between them, the difference in shrinkage during firing, and the difference in thermal expansion coefficient There are problems such as difficulty in obtaining desired characteristics.

  In order to solve this problem, the development of a ferrite material having excellent DC superposition characteristics in the magnetic material itself without structurally providing a magnetic gap has been promoted, and Ni-Zn doped with silicon oxide and zircon oxide is added. Ni-Zn-Cu ferrite (Patent Document 1 and Patent Document 2) and silicon-added Ni-Zn-Cu ferrite (Patent Document 3) are known.

On the other hand, a technique (Patent Document 4 and Patent Document 5) for controlling a change in inductance caused by a stress change by incorporating Zn ₂ SiO ₄ into a Ni—Zn—Cu-based ferrite has been proposed.

JP 2003-112968 A JP 2004-172396 A JP 2005-145781 A JP-A-2-137301 JP 2004-296865 A

  In the aforementioned Patent Documents 1 to 3, by adding silicon oxide and zircon oxide to Ni—Zn or Ni—Zn—Cu ferrite, it is possible to suppress a decrease in magnetic permeability when DC current is superimposed. It is shown. However, since there is no description about the core loss due to the alternating current flowing at the same time, it is difficult to apply the magnetic material itself to a ferrite material having excellent DC superposition characteristics.

  Patent Documents 4 and 5 described above describe a technique for controlling a change in inductance caused by a stress change. However, since there is no description regarding a core loss or a DC superimposition characteristic, the magnetic material itself is excellent in DC superimposition. It is difficult to apply to a ferrite material having characteristics.

  Therefore, the present invention has a technical problem to provide a ferrite material in which the magnetic material itself has excellent DC superposition characteristics.

  The technical problem can be achieved by the present invention as follows.

That is, the present invention is a Ni—Zn ferrite powder containing 42 to 49 mol% Fe ₂ O ₃ , 24 to ₃₀ mol% NiO, and 24 to 30 mol% ZnO, and containing silicon oxide. Thus, it is a Ni-Zn ferrite powder characterized by containing 1.5 to 5 wt% of the silicon oxide (Invention 1).

  Moreover, this invention is a green sheet formed into a sheet form using the Ni-Zn system ferrite powder of this invention 1, and a binding material (this invention 2).

Further, the present invention is, 45～50Mol% of _Fe 2 _O 3, have a ferrite composition comprising a 26～33Mol% of NiO, 17~26mol% of ZnO, _and, Ni-Zn system containing Zn 2 SiO ₄ a ferrite sintered body, a Ni-Zn ferrite sintered body characterized by containing the Zn ₂ SiO ₄ 1.1 ~6wt% (invention 3).

Further, according to the present invention, in the Ni—Zn-based ferrite sintered body of the present invention 3, the real part μ ₀ ′ of the magnetic permeability measured without applying a DC superimposed magnetic field is 25 to 150, and the core loss P ₀ is 1400 kW / m ³ or less, the ratio μ ₁₀₀₀ ′ / μ ₀ ′ of the real part μ ₁₀₀₀ ′ and μ ₀ ′ measured with a DC superimposed magnetic field of 1000 A / m applied is 0.5 or more, and the DC superimposed A Ni—Zn-based ferrite sintered body characterized in that a ratio P ₁₀₀₀ / P _{0 of} core loss P ₁₀₀₀ and P ₀ measured in a state where a magnetic field is applied at 1000 A / m is 0.7 to 1.2. (Invention 4).

  The Ni—Zn-based ferrite powder according to the present invention is suitable as a ferrite powder for an inductance element because the direct current superposition characteristics of a sintered body obtained by sintering the Ni—Zn-based ferrite powder are excellent.

  The green sheet according to the present invention is suitable as a green sheet for an inductance element because the direct current superposition characteristics of a sintered body obtained by sintering the green sheet are excellent.

  The Ni—Zn-based ferrite sintered body according to the present invention is suitable as a ferrite sintered body for an inductance element because of excellent DC superposition characteristics.

  The configuration of the present invention will be described in more detail as follows.

In the present invention, as an indicator of the DC superposition characteristics, the real part μ ₀ ′ of the permeability measured without applying the DC superposition magnetic field and the real part μ of the permeability measured with the DC superposition magnetic field of 1000 A / m applied. using the / μ ₀ '' ratio _{μ 1000} of _'1000. This ratio μ ₁₀₀₀ ′ / μ ₀ ′ indicates the degree of decrease in magnetic permeability when the DC superimposed magnetic field is 1000 A / m with reference to the magnetic permeability when the DC superimposed magnetic field is 0 A / m. This value is usually 1 or less, but as this value is closer to 1, it means that the real part of the magnetic permeability is less likely to decrease when a DC superimposed magnetic field is applied. This indicates that the superimposition characteristics are excellent.

Further, in the present invention, as an index of DC bias characteristics, the ratio P ₁₀₀₀ of the core loss P ₁₀₀₀ measures the DC bias magnetic field core loss P ₀ measured in a state of not applying a DC bias magnetic field while applying 1000A / m / P ₀ was used. This ratio P ₁₀₀₀ / P ₀ indicates the degree of change in the core loss when the DC superimposed magnetic field is 1000 A / m with reference to the core loss when the DC superimposed magnetic field is 0 A / m. When this value is greater than 1, it indicates that the core loss increases when a DC superimposed magnetic field is applied.

  Next, the Ni—Zn ferrite powder according to the present invention will be described.

The Ni—Zn ferrite powder according to the present invention has a composition comprising 42 to 49 mol% Fe ₂ O ₃ , 24 to ₃₀ mol% NiO, and 24 to 30 mol% ZnO, and contains 1 to 5 wt% of silicon oxide. To do.

When the composition of Fe ₂ O ₃ is out of the above range, the DC superimposition characteristics are deteriorated when the powder is used as a sintered body. A preferable composition of Fe ₂ O ₃ is 43 to 48.5 mol%.

When the composition of NiO is less than 24 mol%, μ ₁₀₀₀ ′ / μ ₀ ′ becomes small when the powder is used as a sintered body, and the direct current superimposition characteristics are deteriorated. When the composition of NiO exceeds 30 mol%, μ ₀ ′ becomes small when the powder is made into a sintered body, so that it becomes difficult to obtain a large inductance value when the inductance element is used, and the direct current superimposition characteristic is deteriorated. A preferable composition of NiO is 24.5 to 29.5 mol%.

  When the composition of ZnO is out of the above range, the direct current superimposition characteristics deteriorate when the powder is made into a sintered body. A preferable composition of ZnO is 24 to 29.5 mol%.

  When the content of silicon oxide is out of the above range, the direct current superimposition characteristics deteriorate when the powder is used as a sintered body. The content of silicon oxide is preferably 1 to 4.0 wt%, more preferably 1 to 3.0 wt%, and even more preferably 1 to 2.0 wt%.

  The Ni—Zn-based ferrite powder according to the present invention is a mixture obtained by mixing raw materials such as oxides, carbonates, hydroxides and the like of each element constituting ferrite in a conventional manner, in the atmosphere, from 700 to It can be obtained by calcination after pre-baking for 1 to 20 hours in a temperature range of 1000 ° C.

  The addition timing of silicon oxide is not particularly limited, but is preferably at the time of mixing raw materials.

  Next, the green sheet according to the present invention will be described.

  The green sheet is a paint by mixing the Ni-Zn ferrite powder with a binding material, a plasticizer, a solvent, etc., and the paint is formed to a thickness of several μm to several hundred μm with a doctor blade type coater or the like. And then dried. After the sheets are stacked, pressure is applied to form a laminated body, and the laminated body is sintered at a predetermined temperature to obtain an inductance element.

  The green sheet according to the present invention contains 2 to 20 parts by weight of a binder and 0.5 to 15 parts by weight of a plasticizer with respect to 100 parts by weight of the Ni—Zn ferrite powder according to the present invention. Preferably, the binder contains 4 to 15 parts by weight and the plasticizer 2 to 10 parts by weight. Further, the solvent may remain due to insufficient drying after film formation. Furthermore, you may add well-known additives, such as a viscosity modifier, as needed.

  Examples of the binding material include polyvinyl butyral, polyacrylic acid ester, polymethyl methacrylate, vinyl chloride, polymethacrylic acid ester, ethylene cellulose, abietic acid resin, and the like. A preferred binding material is polyvinyl butyral.

  When the binding material is less than 2 parts by weight, the green sheet becomes brittle, and in order to have strength, a content exceeding 20 parts by weight is not necessary.

  Examples of the plasticizer include benzyl-n-butyl phthalate, butyl butyl phthalyl glycolate, dibutyl phthalate, dimethyl phthalate, polyethylene glycol, phthalate ester, butyl stearate, and methyl agitate.

  When the plasticizer is less than 0.5 parts by weight, the green sheet becomes hard and cracks are likely to occur. When the plasticizer exceeds 15 parts by weight, the green sheet becomes soft and difficult to handle.

  In the production of the green sheet according to the present invention, 15 to 150 parts by weight of the solvent is used with respect to 100 parts by weight of the Ni—Zn ferrite powder. When the solvent is out of the above range, a uniform green sheet cannot be obtained. Therefore, the inductance element obtained by sintering the sheet tends to vary in characteristics.

  The kind of solvent is acetone, benzene, butanol, ethanol, methyl ethyl ketone, toluene, propyl alcohol, isopropyl alcohol, n-butyl acetate, 3methyl-3methoxy-1 butanol, and the like.

The lamination pressure is preferably 0.2 × 10 ^{4 to} 0.6 × 10 ⁴ t / m ² .

  Next, the Ni—Zn ferrite sintered body according to the present invention will be described.

The Ni—Zn-based ferrite sintered body according to the present invention has a composition comprising 45 to 50 mol% Fe ₂ O ₃ , 26 to 33 mol% NiO, and 17 to 26 mol% ZnO, and Zn ₂ SiO ₄ is 1 Contains ~ 6 wt%.

When the composition of Fe ₂ O ₃ is out of the above range, the direct current superposition characteristics are deteriorated. A preferable composition of Fe ₂ O ₃ is 45.5 to 50 mol%.

When the composition of NiO is less than 26 mol%, the direct current superimposition characteristics are deteriorated. When the composition of NiO exceeds 33 mol%, μ ₀ ′ becomes small. Therefore, when an inductance element is used, it is difficult to obtain a large inductance value, and the direct current superimposition characteristic is deteriorated. The preferred NiO composition is 26.5 to 33 mol%, more preferably 26.5 to 32.5 mol%.

  When the composition of ZnO is out of the above range, the direct current superposition characteristics are deteriorated. The composition of ZnO is preferably 17 to 25.5 mol%, more preferably 17.5 to 25.5 mol%.

Zn ₂ SiO ₄ contained in the Ni—Zn ferrite sintered body according to the present invention is composed of silicon oxide contained in the Ni—Zn ferrite powder according to the present invention and Zn in the ferrite component. It is produced by reacting when sintering ferrite powder. When the content of Zn ₂ SiO ₄ is out of the above range, the direct current superposition characteristics are deteriorated. The preferable content of Zn ₂ SiO ₄ is 1 to 5 wt%, more preferably 1 to 4 wt%, and still more preferably 1 to 3 wt%.

The real part μ ₀ ′ of the magnetic permeability of the Ni—Zn ferrite sintered body according to the present invention is 25 to 150. When the real part μ ₀ ′ of the magnetic permeability is less than 25, it is difficult to obtain a large inductance value when an inductance element is used. When the real part μ ₀ ′ of the magnetic permeability exceeds 150, μ ₁₀₀₀ ′ becomes small and the DC superimposition characteristics deteriorate. The real part μ ₀ ′ of the preferable magnetic permeability is 30 to 150, more preferably 60 to 140.

The μ ₁₀₀₀ ′ / μ ₀ ′ of the Ni—Zn ferrite sintered body according to the present invention is 0.5 or more. When μ ₁₀₀₀ ′ / μ ₀ ′ is less than 0.5, only an inductance element having inferior DC superimposition characteristics can be obtained.

The core loss P ₀ of the Ni—Zn ferrite sintered body according to the present invention is 1400 W / m ³ or less. When the core loss P ₀ exceeds 1400 kW / m ³ , the loss as a sintered body increases, so that only inefficient inductance elements can be obtained. Preferred core loss _{P 0} is a 1350kW / ^{m 3} or less, more preferably 1200 kW / ^{m 3} or less, still more preferably 700 kW / ^{m 3} or less.

_P 1000 / _{P 0} of Ni-Zn ferrite sintered body according to the present invention is from 0.70 to 1.20. If it is out of this range, the direct current superimposition characteristic is deteriorated. Preferred P ₁₀₀₀ / P ₀ is 0.80 to 1.20.

The Ni—Zn based ferrite sintered body according to the present invention pressurizes the Ni—Zn based ferrite powder according to the present invention at a pressure of 0.3 to 3.0 × 10 ⁴ t / m ² using a mold. A so-called green sheet method obtained by laminating a green body containing a Ni-Zn ferrite powder according to the present invention, or a molded body obtained by a so-called powder pressure molding method. The body can be obtained by sintering at 1150-1300 ° C. for 1-20 hours, preferably 1-10 hours. As a molding method, a known method can be used, but the above-mentioned powder pressure molding method and the green sheet method are preferable.

  When the sintering temperature is lower than 1150 ° C., the sintered density is lowered, so that the strength of the sintered body is lowered. When the sintering temperature exceeds 1300 ° C., the sintered body is likely to be deformed, making it difficult to obtain a sintered body having a desired shape.

<Action>
The most important point in the present invention contains silicon oxide at a specific ratio, obtained by sintering the Ni-Zn ferrite powder in a specific ferrite composition range consisting of Fe ₂ O _3, NiO and ZnO Ni This is the fact that the Zn-based ferrite sintered body has low core loss and the magnetic material itself has excellent direct current superposition characteristics. The reason why these various characteristics are improved is not yet clear, but the added silicon oxide reacts with Zn in the ferrite component to form Zn ₂ SiO ₄ , which is present at the ferrite grain boundary. The present inventor believes that the magnetization curve of the Ni—Zn ferrite sintered body has a gentle slope as compared with the case where no Zn ₂ SiO ₄ is contained, and further changes linearly. Is estimating.

  A typical embodiment of the present invention is as follows.

  An X-ray diffractometer RINT2500 (manufactured by Rigaku Corporation) was used for identification of the generated phase.

  The compositions of the Ni—Zn ferrite powder and the Ni—Zn ferrite sintered body were measured using a fluorescent X-ray analyzer RIX2100 (manufactured by Rigaku Corporation).

The content of Zn ₂ SiO ₄ contained in the Ni—Zn-based ferrite sintered body is determined by X-ray diffraction. The Ni—Zn-based ferrite sintered body is composed of a spinel ferrite phase and a Zn ₂ SiO ₄ phase. After confirming this, the silicon content measured using a fluorescent X-ray analyzer RIX2100 (manufactured by Rigaku Denki Kogyo Co., Ltd.) was taken as a value converted to the Zn ₂ SiO ₄ content.

The permeability μ ₀ ′ of the Ni—Zn-based ferrite sintered body is set to BH / Z in a state where a winding is applied to the ring-shaped sintered body, the frequency is 1 MHz, the magnetic flux density is 25 mT, and no DC superimposed magnetic field is applied. The value of the real part of the magnetic permeability measured using an analyzer E5060A (manufactured by Agilent Technologies) was used.

The permeability μ ₁₀₀₀ ′ of the Ni—Zn-based ferrite sintered body is B−H in a state where a winding is applied to the ring-shaped sintered body, the frequency is 1 MHz, the magnetic flux density is 25 mT, and the DC superimposed magnetic field is 1000 A / m. / Z analyzer E5060A (manufactured by Agilent Technologies) was used as the value of the real part of the magnetic permeability. μ ₁₀₀₀ ′ / μ ₀ ′ was obtained by calculation from μ ₀ ′ and μ ₁₀₀₀ ′.

The core loss P ₀ of the Ni—Zn ferrite sintered body is obtained by applying a winding to the ring-shaped sintered body, setting the frequency to 1 MHz, setting the magnetic flux density to 25 mT, and applying the DC superimposed magnetic field to the BH / Z analyzer. and the value of the _{P cv,} which was measured by using the E5060A (manufactured by Agilent technology Co., Ltd.).

Ni-Zn-based core loss _{P 1000} of the ferrite sintered body is subjected to winding to the ring-shaped sintered body, 1MHz frequency, 25 mT magnetic flux density, in a state where the DC bias magnetic field was applied 1000A / m B-H / and the value of _{P cv} measured using Z analyzer E5060A (manufactured by Agilent technologies Inc.). _{P 1000} / P ₀ was calculated from _{P 0} and _{P 1000.}

Example 1
<Production of Ni-Zn ferrite powder>
Each oxide raw material is weighed so that the composition of the Ni—Zn ferrite is approximately Fe ₂ O ₃ = 46 mol%, NiO = 27 mol%, ZnO = 27 mol%, and the content of silicon oxide is 1 wt%. After adding silicon oxide as described above and performing wet mixing for 30 minutes using an attritor, the mixed slurry was filtered and dried to obtain a raw material mixed powder. A calcined product obtained by calcining the raw material mixed powder at 900 ° C. for 2 hours was coarsely pulverized with an atomizer and then finely pulverized with a vibration mill to obtain a Ni—Zn ferrite powder.

The composition of the obtained Ni—Zn-based ferrite powder is Fe ₂ O ₃ = 45.9 mol%, NiO = 27.2 mol%, ZnO = 26.9 mol% as the ferrite composition, and the Ni—Zn ferrite powder is the standard. As a result, the content of silicon oxide was 1.0 wt%.

<Manufacture of green sheets>
7 parts by weight of polyvinyl butyral as a binder, 4.5 parts by weight of benzyl-n-butyl phthalate as a plasticizer, and 30 parts by weight of n-butyl acetate as a solvent with respect to 100 parts by weight of the obtained Ni—Zn ferrite powder After adding 30 parts by weight of methyl ethyl ketone, it was mixed well to obtain a slurry. This slurry was applied onto a PET film by a doctor blade type coater to form a coating film, and then dried to obtain a green sheet having a thickness of 75 μm. This was cut into a size of 100 mm length × 100 mm width, 7 layers were laminated, and then pressed with a pressure of 0.35 × 10 ⁴ t / m ² to obtain a green sheet laminate having a thickness of 0.52 mm. .

<Manufacture of Ni-Zn ferrite sintered body>
The obtained green sheet laminate was sintered at 1230 ° C. for 2 hours to obtain a Ni—Zn ferrite sintered body having a thickness of 0.43 μm. The X-ray diffraction pattern of the Ni—Zn-based ferrite sintered body was composed of two phases of a spinel ferrite phase and a Zn ₂ SiO ₄ phase, and no other different phases were observed. The composition of the Ni-Zn ferrite sintered body is Fe ₂ O ₃ = 47.8 mol%, NiO = 29.3 mol%, ZnO = 22.9 mol% as the ferrite composition. Based on the body, the content of Zn ₂ SiO ₄ was 1.4 wt%. A ring-shaped sintered body having an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 0.43 mm was cut out from the obtained Ni—Zn-based ferrite sintered body by an ultrasonic processing machine, and the magnetic properties were evaluated. The sintered body had a μ ₀ ′ of 128, a μ ₁₀₀₀ ′ / μ ₀ ′ of 0.55, a core loss P ₀ of 598 kW / m ³ , and a P ₁₀₀₀ / P ₀ of 1.08.

Example 2 to Example 4, Example 9 to Example 10
In the same manner as in Example 1, a Ni—Zn ferrite sintered body was obtained. Tables 1 and 2 show the manufacturing conditions and the characteristics of the obtained Ni—Zn ferrite sintered body.

Example 5
A Ni—Zn ferrite powder similar to that of Example 1 was prepared, and 1.5 g of a mixed powder obtained by mixing 10 parts by weight of a 6% aqueous solution of polyvinyl alcohol with 100 parts by weight of the Ni—Zn ferrite powder. Using a mold, it was pressure-molded to an outer diameter of 16 mm, an inner diameter of 9.5 mm, and a thickness of 3.5 mm with a molding pressure of 0.75 × 10 ⁴ t / m ² . This molded body was sintered at a sintering temperature of 1200 ° C. for 3 hours to obtain a Ni—Zn ferrite sintered body.

  Tables 1 and 2 show the manufacturing conditions and the characteristics of the obtained Ni—Zn ferrite sintered body.

Example 6 to Example 8
In the same manner as in Example 5, a Ni—Zn-based ferrite sintered body was obtained. Tables 1 and 2 show the manufacturing conditions and the characteristics of the obtained Ni—Zn ferrite sintered body.

Comparative Examples 1 to 5 and Comparative Example 9
A Ni—Zn-based ferrite sintered body was obtained in the same manner as in Example 1 or Example 5. Tables 1 and 2 show the manufacturing conditions and the characteristics of the obtained Ni—Zn ferrite sintered body.

Comparative Example 6 to Comparative Example 8
A Ni—Zn—Cu ferrite sintered body was obtained in the same manner as in Example 1 except that CuO was added to the ferrite composition. Tables 1 and 2 show the production conditions and the characteristics of the obtained Ni—Zn—Cu ferrite sintered body.

As is apparent from the examples, 45~50mol% of _Fe 2 _O 3, a Ni-Zn ferrite sintered body having a composition consisting 26～33Mol% of NiO, 17~26mol% of ZnO, Zn ₂ A Ni—Zn-based ferrite sintered body containing 1 to 6 wt% of SiO ₄ is suitable as a magnetic material for an inductance element because it has low core loss and the magnetic material itself has excellent direct current superposition characteristics.

Further, 42~49mol% of _Fe 2 _O 3, 24~30mol% of NiO, a Ni-Zn ferrite powder having a composition consisting 24～30Mol% of ZnO, Ni containing silicon oxide 1-5 wt% The -Zn-based ferrite powder is suitable as a magnetic material for an inductance element because a sintered body obtained by sintering it has a small core loss and the magnetic material itself has excellent direct current superposition characteristics.

In addition, a green sheet formed into a sheet shape using the Ni-Zn ferrite powder and a binding material has a small core loss and a magnetic material itself that has a sintered body obtained by sintering the green sheet. Since it has excellent direct current superposition characteristics, it is suitable as a magnetic material for an inductance element.

Claims (4)

A Ni—Zn ferrite powder having a ferrite composition comprising 42 to 49 mol% Fe ₂ O ₃ , 24 to ₃₀ mol% NiO, and 24 to 30 mol% ZnO, and containing silicon oxide, A Ni—Zn-based ferrite powder characterized by containing 1.5 to 5 wt% of silicon. The green sheet formed into a sheet form using the Ni-Zn type ferrite powder of Claim 1, and a binding material. A Ni—Zn ferrite sintered body having a ferrite composition comprising 45 to 50 mol% Fe ₂ O ₃ , 26 to 33 mol% NiO, and 17 to 26 mol% ZnO, and containing Zn ₂ SiO _4. A Ni—Zn based ferrite sintered body containing 1.1 to 6 wt% of the Zn ₂ SiO ₄ . 4. The Ni—Zn ferrite sintered body according to claim 3, wherein the real part μ ₀ ′ of the magnetic permeability measured without applying a DC superimposed magnetic field is 25 to 150, and the core loss P ₀ is 1400 kW / m ³ or less. The ratio μ ₁₀₀₀ ′ / μ ₀ ′ of the real part μ ₁₀₀₀ ′ and μ ₀ ′ of the magnetic permeability measured with a DC superimposed magnetic field of 1000 A / m applied is 0.5 or more, and the DC superimposed magnetic field is 1000 A / m A Ni—Zn-based ferrite sintered body characterized in that a ratio P ₁₀₀₀ / P _{0 of} the core loss P ₁₀₀₀ and P ₀ measured in an applied state is 0.7 to 1.2.