US-12623282-B2 - Method for producing composite magnetic body, magnetic powder, composite magnetic body and coil component

Abstract

A method for producing a composite magnetic body includes: pressure molding a metal magnetic material into a predetermined shape, the metal magnetic material being an Fe—Si-based metal magnetic material; performing a primary heat treatment of heating the metal magnetic material in an atmosphere with a first oxygen partial pressure to form an Si oxide coating film on a surface of the metal magnetic material; and performing a secondary heat treatment of heating the metal magnetic material that has undergone the primary heat treatment in an atmosphere with a second oxygen partial pressure, which is higher than the first oxygen partial pressure, to form an Fe oxide layer at least partially on a surface of the Si oxide coating film.

Inventors

• Takeshi Takahashi

Assignees

• PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.

Dates

Publication Date

20260512

Application Date

20220608

Priority Date

20170331

Claims (3)

1. 1 . A magnetic powder, comprising: a metal magnetic material that is an Fe—Si-based metal magnetic material; an Si oxide coating film that covers a surface of the metal magnetic material; and an Fe oxide layer that is formed at least partially on a surface of the Si oxide coating film.
2. 2 . A composite magnetic body comprising: a plurality of particles of the magnetic powder according to claim 1 , and a resin binder impregnated in the composite magnetic body and present between adjacent ones of the plurality of particles, wherein: the composite magnetic body is obtained by pressure molding the plurality of particles into a predetermined shape, and the resin binder contacts the Fe oxide layer in regions where the Fe oxide layer is present.
3. 3 . A coil component, comprising: the composite magnetic body according to claim 2 ; and a conductor that is wound around the composite magnetic body.

Description

CROSS-REFERENCE OF RELATED APPLICATIONS This application is a Divisional of U.S. patent application Ser. No. 16/496,835, filed on Sep. 23, 2019, now U.S. Pat. No. 11,651,892, which in turn claims the benefit of the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2018/010689, filed on Mar. 19, 2018, which in turn claims the benefit of Japanese Application No. 2017-070893, filed on Mar. 31, 2017, the entire disclosures of which Applications are incorporated by reference herein. TECHNICAL FIELD The present disclosure relates to a method for producing a composite magnetic body, a magnetic powder, a composite magnetic body, and a coil component. BACKGROUND ART Conventionally, metal magnetic materials and oxide magnetic materials such as ferrite are used as magnetic materials for forming magnetic cores for use in inductors and transformers. A magnetic core made of ferrite has a small saturation magnetic flux density and poor DC superimposition characteristics. For this reason, in order to ensure DC superimposition characteristics, a ferrite magnetic core has a gap with several hundreds μm in a direction perpendicular to the magnetic path. However, such a wide gap serves as a beat noise generator, and also a leakage magnetic flux generated from the gap causes a significant increase in copper loss in a coil particularly in a high frequency band. As magnetic cores made of metal magnetic material, there are a laminated magnetic core in which a silicon steel plate and the like are laminated, and a pressed powder magnetic core obtained by compression molding a metal powder. The laminated magnetic core is not suitable for use at high frequencies because it is difficult to form a thin steel plate and the loss caused by an eddy current is large at high frequencies. In contrast, the pressed powder magnetic core has a saturation magnetic flux density much larger than that of the ferrite magnetic core, and it is therefore advantageous in terms of miniaturization. In addition, unlike the ferrite magnetic core, the pressed powder magnetic core can be used without a gap. Accordingly, the beat noise and the copper loss caused by a leakage magnetic flux are small. Furthermore, the pressed powder magnetic core can be formed through molding, and thus has a high degree of freedom in the product shape. Also, even a pressed powder magnetic core with a complex shape can be produced with a simple process, and thus attention is paid to the usability thereof (see, for example, Patent Literature (PTL) 1). PTL 1 discloses a magnetic powder composed mainly of iron (Fe) and silicon (Si) as composite magnetic materials, and a pressed powder magnetic core. According to PTL 1, an insulating coating film is formed on the surface of a magnetic powder composed mainly of Fe and Si. The insulating coating film is obtained by subjecting the magnetic powder to an external oxidation treatment. CITATION LIST Patent Literature PTL 1: Japanese Unexamined Patent Application Publication No. 2005-146315 SUMMARY OF THE INVENTION Technical Problem In order to impart high magnetic characteristics to a composite magnetic material, it is effective to perform a heat treatment at a high temperature in order to reduce the residual stress of the molded composite magnetic material. However, performing a heat treatment at a high temperature is problematic in that the insulating coating film formed on the surface of the metal magnetic material is damaged, and the size of the loop of eddy current increases, causing an increase in eddy current loss. For this reason, there has conventionally been a problem in that a heat treatment cannot be performed at a high temperature, and it is therefore difficult to impart high magnetic characteristics. In view of the problem described above, it is an object of the present invention to provide a method for producing a composite magnetic body with high magnetic characteristics, a magnetic powder, a composite magnetic body, and a coil component. Solutions to Problem A method for producing a composite magnetic body according to one aspect of the present disclosure includes: pressure molding a metal magnetic material into a predetermined shape, the metal magnetic material being an Fe—Si-based metal magnetic material; performing a primary heat treatment of heating the metal magnetic material in an atmosphere with a first oxygen partial pressure to form an Si oxide coating film on a surface of the metal magnetic material; and performing a secondary heat treatment of heating the metal magnetic material that has undergone the primary heat treatment in an atmosphere with a second oxygen partial pressure, which is higher than the first oxygen partial pressure, to form an Fe oxide layer at least partially on a surface of the Si oxide coating film. Also, a magnetic powder according to one aspect of the present disclosure includes: a metal magnetic material that is an Fe—Si-based metal magnetic material; an