Method for manufacturing an Fe-based nanocrystalline alloy magnetic core and Fe-based nanocrystalline alloy magnetic core

Abstract

The present invention is a method for producing an Fe-based nanocrystalline alloy magnetic core, said method including an oxide film forming step for heat-treating, in an oxidizing atmosphere, a magnetic core material in which a nanocrystallizable Fe-based alloy ribbon is wound, and a nanocrystallization step for carrying out nanocrystallization of the nanocrystallizable Fe-based alloy by heat-treating, in a non-oxidizing atmosphere, the magnetic core material after the oxide film forming step, wherein a maximum temperature of the heat treatment in the oxide film forming step is a temperature lower than the crystallization start temperature of the nanocrystallizable Fe-based alloy, and a maximum temperature of the heat treatment in the nanocrystallization step is a temperature greater than or equal to the crystallization start temperature of the nanocrystallizable Fe-based alloy.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an Fe-based nanocrystalline alloy core and an Fe-based nanocrystalline alloy core.

Background Art

[0002] Since Fe-based nanocrystalline alloys have excellent soft magnetic properties that can achieve high magnetic permeability, they are used in cores such as common mode chokes and high-frequency transformers. As a typical composition of Fe-based nanocrystalline alloys, a magnetic material of Fe-Si-B-Cu-Nb-based nanocrystals with Fe as the main component is known (Patent Document 1). Coils and cores using such magnetic materials are generally obtained by winding a ribbon of an Fe-based amorphous alloy that can be nanocrystallized to form a cylindrical wound core and performing heat treatment.

[0003] Higher magnetic permeability is required for cores, and technologies for improving magnetic permeability have been actively developed in addition to material selection. For example, Patent Documents 2 and 3 disclose a technique for improving magnetic permeability in the high-frequency region by forming an oxide film on the surface of a magnetic ribbon in a core formed by winding or laminating a ribbon of an amorphous magnetic alloy. This technique suppresses the generation of eddy currents flowing between ribbon layers of a core formed by winding or laminating a magnetic ribbon by insulating the ribbon layers with an oxide film, thereby reducing eddy current loss. As a result, the magnetic permeability is improved. Further, Patent Document 4 discloses a technique for adjusting crystalline magnetic anisotropy and improving magnetic permeability by applying a magnetic field while performing heat treatment on a core using a nanocrystalline alloy material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] In recent years, for example, magnetic cores used in common mode chokes are required to be able to adequately handle low frequencies. In magnetic cores formed by winding or laminating nanocrystalline alloy magnetic ribbons, the generation of eddy currents flowing between ribbon layers can be suppressed by forming an oxide film on the surface of the magnetic ribbons, thereby improving the magnetic permeability in the high-frequency range. However, unlike amorphous alloy magnetic cores as described in Patent Documents 2 and 3, nanocrystalline alloy magnetic cores tend to have a decrease in magnetic permeability in the low-frequency range due to the formation of an oxide film. Although it is possible to improve the magnetic permeability in the low-frequency range of nanocrystalline alloy magnetic cores by applying a magnetic field, the problem remains that the degree of improvement is not sufficient.

[0006] In view of the above-mentioned problems, the present invention aims to provide a method for manufacturing an Fe-based nanocrystalline alloy magnetic core that exhibits high magnetic permeability in the low-frequency region. [Means for solving the problem]

[0007] As a result of repeated studies to solve the above problems, the inventors of the present invention have found that by forming an oxide film on the surface of the Fe-based alloy ribbon in a magnetic core material in which the Fe-based alloy ribbon is wound, and then nanocrystallizing the Fe-based alloy in an environment in which no oxide film is formed, an Fe-based nanocrystalline alloy magnetic core exhibiting high magnetic permeability even in the low-frequency region can be obtained, leading to the present invention. In other words, the gist of the present invention is as follows.

[0008] [1] An oxide film formation process in which a magnetic core material, which is made of a ribbon of a nanocrystallizable Fe-based alloy wound around it, is heat-treated in an oxidizing atmosphere, and The process includes a nanocrystallization step in which the core material after the oxide film formation step is heat-treated in a non-oxidizing atmosphere to nanocrystallize the Fe-based alloy that can be nanocrystallized, The maximum temperature of the heat treatment in the oxide film formation step is below the crystallization start temperature of the nanocrystallizable Fe-based alloy. A method for manufacturing an Fe-based nanocrystalline alloy magnetic core, wherein the maximum temperature of the heat treatment in the nanocrystallization step is a temperature equal to or greater than the crystallization initiation temperature of the Fe-based alloy that can be nanocrystallized. [2] The process includes a magnetic field application step in which a magnetic field is applied to the magnetic core material in the height direction while heat treatment is applied to the magnetic core material after the nanocrystallization step, A method for producing an Fe-based nanocrystalline alloy magnetic core according to [1], wherein the maximum temperature of the heat treatment in the magnetic field application step is a temperature below the crystallization start temperature of the Fe-based alloy that can be nanocrystallized. [3] A method for producing an Fe-based nanocrystalline alloy magnetic core according to [1] or [2], wherein the nanocrystalline Fe-based alloy has a composition represented by the following general formula (I). Fe x Si a B b Cu c Nb d (I) (In general formula (I), a to d (atomic %) represent 3.0 ≤ a ≤ 12.0, 1.0 ≤ b ≤ 7.0, 1.0 ≤ c ≤ 5.0, and 1.0 ≤ d ≤ 9.0, respectively; x (atomic %) is the remainder other than Si, B, Cu, and Nb, satisfying 73.0 ≤ x ≤ 92.0.) [4] It is a magnetic core made by winding a ribbon, The ribbon has, in this order, a first oxide film layer, a second oxide film layer, and a base material formed of an Fe-based nanocrystalline alloy containing an amorphous phase and crystalline grains. The Fe-based nanocrystalline alloy has a composition represented by the following general formula (I): A Fe-based nanocrystalline alloy magnetic core that satisfies the following conditions (A) and (B) in the depth profile obtained by X-ray photoelectron spectroscopy of sample X below. Fe x Si a Bb Cu c Nb d (I) (In general formula (I), a to d (atomic %) respectively represent 3.0 ≤ a ≤ 12.0, 1.0 ≤ b ≤ 7.0, 1.0 ≤ c ≤ 5.0, and 1.0 ≤ d ≤ 9.0; x (atomic %) is the remainder other than Si, B, Cu, and Nb, and satisfies 73.0 ≤ x ≤ 92.0.) (A) A peak of Cu appears in the depth range corresponding to the first oxide film layer. 2p (B) In the depth range corresponding to the first oxide film layer, the intensity of the Cu peak is stronger than the intensity of O derived from SiO2. 2p 1S (Sample X) When the inner peripheral surface and the outer peripheral surface of the Fe-based nanocrystalline alloy core are virtually divided into three regions: a first region, a second region, and a third region from the inner peripheral surface toward the outer peripheral surface, a ribbon located within the second region is cut out as the sample. The first region, the second region, and the third region are regions that divide the radial length between the inner peripheral surface and the outer peripheral surface into 40 / 20 / 40. X-ray photoelectron spectroscopy is performed on the surface of the sample that faced the outer peripheral surface when the Fe-based nanocrystalline alloy core was formed during winding. [5]<00—0150>The Fe-based nanocrystalline alloy core according to [4], further satisfying the following (C) and (D) in the depth profile. (C) Peaks of O derived from SiO2 and Si appear in the depth range corresponding to the second oxide film layer. 1S 2p (D) In the depth range corresponding to the second oxide film layer, the intensity of the peak of O derived from SiO2 is stronger than the intensity of Cu. 1S 2p [6] The Fe-based nanocrystalline alloy core according to [4] or [5], further satisfying the following (E) in the depth profile. (E) The intensity of the Cu peak in the depth range corresponding to the first oxide film layer is... 2p the intensity of Cu in the depth range corresponding to the base material.2p It is stronger than [the other] strength. [Effects of the Invention]

[0009] According to the present invention, a method for manufacturing an Fe-based nanocrystalline alloy magnetic core that exhibits high magnetic permeability in the low-frequency region can be provided. Furthermore, according to a preferred embodiment of the present invention, a method for manufacturing an Fe-based nanocrystalline alloy magnetic core that exhibits high magnetic permeability in both the low-frequency and high-frequency regions can be provided. Furthermore, according to the present invention, the above manufacturing method makes it possible to provide an Fe-based nanocrystalline alloy magnetic core that exhibits high magnetic permeability in the low-frequency region. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the relative permeability at a frequency of 10 kHz for Fe-based nanocrystalline alloy magnetic cores obtained in experimental and comparative examples. [Figure 2] This graph shows the relative permeability at a frequency of 100 kHz for Fe-based nanocrystalline alloy magnetic cores obtained in experimental and comparative examples. [Figure 3] This is a schematic diagram illustrating sample X for X-ray photoelectron spectroscopy analysis. [Figure 4] These are TEM images of the cross-sections of the ribbons forming the Fe-based nanocrystalline alloy magnetic cores obtained in Example 2, Comparative Example 2, and Comparative Example 4 (photograph used as a substitute for drawing). [Figure 5] This is the depth profile obtained by X-ray photoelectron spectroscopy analysis of the Fe-based nanocrystalline alloy magnetic core obtained in Example 2. [Figure 6] This is the depth profile obtained by X-ray photoelectron spectroscopy analysis of the Fe-based nanocrystalline alloy magnetic core obtained in Comparative Example 2. [Figure 7] This is the depth profile obtained by X-ray photoelectron spectroscopy analysis of the Fe-based nanocrystalline alloy magnetic core obtained in Comparative Example 4. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below. The following description of the constituent elements is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents unless it exceeds the gist of the invention. In this specification, when "~" is used to enclose numerical values ​​or physical properties, it is intended to include the values ​​before and after it.

[0012] <1. Method for manufacturing Fe-based nanocrystalline alloy magnetic cores> A method for manufacturing an Fe-based nanocrystalline alloy magnetic core according to the first embodiment of the present invention includes an oxide film formation step of heat-treating a magnetic core material, which is made by winding a ribbon of a nanocrystallizable Fe-based alloy, in an oxidizing atmosphere, and a nanocrystallization step of heat-treating the magnetic core material after the oxide film formation step in a non-oxidizing atmosphere to nanocrystallize the Fe-based alloy. Here, the maximum temperature of the heat treatment in the oxide film formation step is below the crystallization start temperature of the nanocrystallizable Fe-based alloy, and the maximum temperature of the heat treatment in the nanocrystallization step is above the crystallization start temperature of the nanocrystallizable Fe-based alloy.

[0013] In this specification, unless otherwise specified, the heat treatment temperature refers to the set temperature of the heat treatment furnace used for heat treatment of the magnetic core material. The temperature of the magnetic core material itself is approximately 5°C to 10°C higher than the set temperature of the heat treatment furnace and can be measured by attaching a thermocouple to the magnetic core material.

[0014] The Fe-based nanocrystalline alloy magnetic core obtained by the manufacturing method according to this embodiment exhibits high magnetic permeability in the low-frequency region. In this specification, "relative magnetic permeability" may be used as an index for evaluating "magnetic permeability". In this specification, the permeability in the low-frequency region is evaluated based on the permeability at a frequency of 10 kHz. Furthermore, the permeability in the high-frequency region is evaluated based on the permeability at a frequency of 100 kHz.

[0015] The relative permeability of an Fe-based nanocrystalline alloy magnetic core can be calculated by measuring the inductance of a coil wound around the Fe-based nanocrystalline alloy magnetic core and using the following formula (1). μr = μ / μ0 (1) μr: relative permeability μ0: Permeability of vacuum = 4π × 10 -7 [H / m] μ: Magnetic permeability [H / m]=Ll / A / N 2 L: Inductance [H] l: Magnetic path length [m] A: Core effective cross-sectional area [m²] 2 ] N: Number of turns

[0016] The manufacturing method according to this embodiment is similar to conventional manufacturing methods (see, for example, Patent Documents 2 and 3) in that it is a method for producing an Fe-based nanocrystalline alloy magnetic core on which an oxide film capable of suppressing eddy currents has been formed. However, unlike conventional manufacturing methods, it can achieve improved magnetic permeability in the low-frequency region. In conventional manufacturing methods, heat treatment under an oxidizing atmosphere causes the formation of an oxide film and nanocrystallization to proceed simultaneously. In contrast, the manufacturing method according to this embodiment forms an oxide film without causing nanocrystallization in the oxide film formation step, and performs nanocrystallization of the Fe-based alloy without forming an oxide film that would affect the magnetic permeability in the nanocrystallization step. The inventors of this embodiment speculate that by performing the formation of the oxide film and nanocrystallization separately in this order, and preventing the formation of the oxide film and nanocrystallization from proceeding simultaneously, the magnetic permeability in the low-frequency region can be improved.

[0017] <1-1. Oxide film formation process> The oxide film formation process involves heat-treating a magnetic core material, which is made up of ribbons of a nanocrystalline Fe-based alloy (hereinafter sometimes simply referred to as "Fe-based alloy"), in an oxidizing atmosphere to form an oxide film on the surface of the Fe-based alloy ribbons. The maximum temperature of the heat treatment in the oxide film formation process is below the crystallization initiation temperature of the Fe-based alloy.

[0018] The Fe-based alloy constituting the Fe-based alloy ribbon is not particularly limited as long as it is an Fe-based alloy that can be nanocrystallized by heat treatment, for example, Fe-Si-B-Cu-Nb alloys. Specific compositions of Fe-Si-B-Cu-Nb alloys are preferably exemplified by the composition represented by the following general formula (I).

[0019] Fe x Si a B b Cu c Nb d (I) In general formula (I), a to d (atomic %) represent 3.0 ≤ a ≤ 12.0, 1.0 ≤ b ≤ 7.0, 1.0 ≤ c ≤ 5.0, and 1.0 ≤ d ≤ 9.0, respectively; x (atomic %) is the remainder other than Si, B, Cu, and Nb, satisfying 73.0 ≤ x ≤ 92.0. This remainder may include unavoidable impurities.

[0020] The crystallization initiation temperature for nanocrystallizable Fe-based alloys is typically between 350°C and 520°C. In the case of Fe-Si-B-Cu-Nb alloys having the composition represented by the above general formula (I), the crystallization initiation temperature is typically between 480°C and 520°C.

[0021] In this specification, the crystallization initiation temperature is defined as the temperature at which the exothermic reaction due to the initiation of nanocrystallization is detected when the differential scanning calorimeter (DSC) is measured under conditions of a heating rate of 10°C / min.

[0022] The thickness and width of the Fe-based alloy ribbon are not particularly limited as long as it can be wound to form a magnetic core of a practical shape. Specifically, the thickness of the ribbon is usually between 8 μm and 25 μm, and the width of the ribbon is usually between 5 mm and 25 mm.

[0023] As the core material, commercially available core materials may be used as is, or core materials made by winding commercially available Fe-based alloy ribbons may be used. Alternatively, Fe-based alloy ribbons may be made by rapidly cooling and solidifying molten Fe-based alloy using an ultra-rapid cooling method, and then winding these ribbons to produce the core material. In the above-described ultra-rapid cooling method, it is desirable that the temperature of the molten metal during rapid cooling be approximately 50°C to 300°C higher than the melting point of the alloy. The ultra-rapid cooling method is not particularly limited, and known methods such as the single-roll method, double-roll method, rotating liquid-based prevention method, gas atomization method, and water atomization method can be employed. The production of Fe-based alloy ribbons by the ultra-rapid cooling method may be carried out under an oxidizing atmosphere such as air, under an inert gas atmosphere such as argon, helium, or nitrogen, or under vacuum conditions.

[0024] Fe-based alloy ribbons typically consist of an amorphous phase. While it is preferable that Fe-based alloy ribbons do not contain a crystalline phase, they may contain a portion of the crystalline phase as long as it does not hinder the effects of the present invention.

[0025] As the oxidizing atmosphere, an oxygen-containing atmosphere such as oxygen gas or air can be used. The lower limit of the oxygen concentration in the oxygen-containing atmosphere is not particularly limited as long as an oxide film can be formed on the surface of the Fe-based alloy ribbon, and is usually 0.1 vol% or higher, but may be 0.2 vol% or higher, 0.3 vol% or higher, 1.0 vol% or higher, 10.0 vol% or higher, or 20.0 vol% or higher. The upper limit of the oxygen concentration in the oxygen-containing atmosphere is usually 100% or lower, but may be 80.0 vol% or lower, 60.0 vol% or lower, or 40.0 vol% or lower. In other words, suitable ranges for the oxygen concentration in the oxygen-containing atmosphere include 0.1 vol% to 80.0 vol%, 0.2 vol% to 100%, 0.3 vol% to 60.0 vol%, 1.0 vol% to 60.0 vol%, 10.0 vol% to 40.0 vol%, and 20.0 vol% to 40.0 vol%. Moisture may be added to the oxidizing atmosphere by means of a humidifying gas, superheated steam, etc. Furthermore, in the oxide film formation process, the core material may be boiled before heat treatment in an oxidizing atmosphere.

[0026] The maximum temperature for heat treatment in the oxide film formation process is usually 300°C or higher, preferably 400°C or higher, although this depends on the type of oxidizing atmosphere, the heat treatment time, etc. It is also usually below the crystallization start temperature of the Fe-based alloy, preferably 50°C or lower than the crystallization start temperature of the Fe-based alloy, more preferably 60°C or lower than the crystallization start temperature of the Fe-based alloy, and even more preferably 70°C or lower than the crystallization start temperature of the Fe-based alloy. In other words, suitable ranges for the maximum heat treatment temperature include 400°C or higher and 50°C or lower than the crystallization start temperature of the Fe-based alloy, 300°C or higher and below the crystallization start temperature of the Fe-based alloy, 400°C or higher and 60°C or lower than the crystallization start temperature of the Fe-based alloy, and 400°C or higher and 70°C or lower than the crystallization start temperature of the Fe-based alloy. By keeping the maximum temperature within the above range, it is possible to form an oxide film on the surface of the Fe-based alloy ribbon constituting the magnetic core material while simultaneously suppressing the formation of the oxide film and the nanocrystallization of the Fe-based alloy. This makes it possible to improve the magnetic permeability of the Fe-based nanocrystalline alloy magnetic core in the low-frequency range. The heating rate to reach the maximum temperature and the cooling rate after the maximum temperature has been maintained are not particularly limited, as long as they do not hinder the effects of the present invention, and rates generally used in heat treatment in the art of the present invention can be applied. The holding time at the above-mentioned maximum temperature depends on the type of oxidizing atmosphere, the heat treatment temperature, etc., but is usually 1 hour or more, preferably 2 hours or more, more preferably 3 hours or more, and also usually 30 hours or less, preferably 20 hours or less, more preferably 10 hours or less. In other words, suitable ranges for the holding time at the above-mentioned maximum temperature include 1 hour to 20 hours, 2 hours to 30 hours, and 3 hours to 10 hours.

[0027] <1-2. Nanocrystallization process> The nanocrystallization process involves heat-treating the magnetic core material after the oxide film formation process in a non-oxidizing atmosphere to induce nanocrystallization of the Fe-based alloy. The maximum heat treatment temperature in the nanocrystallization process is above the crystallization initiation temperature of the Fe-based alloy. The nanocrystallization process forms an Fe-based nanocrystalline alloy containing crystalline grains consisting of a crystalline phase (bcc phase) and an amorphous phase.

[0028] In this specification, a non-oxidizing atmosphere means an atmosphere that can suppress the formation of an oxide film to the extent that it does not affect the magnetic permeability. Specifically, such a non-oxidizing atmosphere includes inert gas atmospheres such as argon, helium, and nitrogen. The non-oxidizing atmosphere may contain trace amounts of oxygen. If the non-oxidizing atmosphere contains oxygen, its oxygen concentration is usually less than 0.1 vol%, preferably 0.01 vol% or less, and more preferably 0.001 vol% or less.

[0029] The lower limit of the maximum heat treatment temperature in the nanocrystallization process is not particularly limited as long as it is above the crystallization start temperature of the Fe-based alloy, and is preferably 14°C higher than the crystallization start temperature of the Fe-based alloy. The upper limit of the maximum heat treatment temperature in the nanocrystallization process is usually 59°C higher than the crystallization start temperature of the Fe-based alloy, and is preferably 44°C higher than the crystallization start temperature of the Fe-based alloy. More specifically, if the crystallization start temperature of the Fe-based alloy is around 516°C, the heat treatment temperature in the nanocrystallization process is usually 516°C or higher, preferably 530°C or higher, and is usually 575°C or lower, and is preferably 560°C or lower. In other words, preferred ranges for the maximum heat treatment temperature include temperatures 14°C higher than the crystallization onset temperature of the Fe-based alloy and 59°C higher than the crystallization onset temperature of the Fe-based alloy, and temperatures 14°C higher than the crystallization onset temperature of the Fe-based alloy and 44°C higher than the crystallization onset temperature of the Fe-based alloy. More specifically, ranges of 516°C to 560°C and 530°C to 575°C are included. The heating rate to reach the maximum temperature and the cooling rate after the maximum temperature has been maintained are not particularly limited, as long as they do not hinder the effects of the present invention, and rates generally used in heat treatment in the art of the present invention can be applied. The holding time at the above-mentioned maximum temperature depends on the composition of the Fe-based alloy, the size of the magnetic core, etc., but from the viewpoint of uniformly heating the entire alloy and productivity, it is usually 30 minutes or more, preferably 50 minutes or more, more preferably 90 minutes or more, and also usually 10 hours or less, preferably 2 hours or less. In other words, suitable ranges for the holding time at the above-mentioned maximum temperature include 30 minutes to 2 hours, 50 minutes to 10 hours, and 90 minutes to 10 hours.

[0030] The nanocrystallization process may further include a heat retention step in which, during the process of raising the temperature to the maximum temperature described above, the heating is temporarily stopped when the heat treatment temperature reaches a level below the maximum temperature, and the heat treatment temperature is maintained.

[0031] During the nanocrystallization of Fe-based alloys, overshoot can occur due to self-heating during the precipitation of the crystalline phase, causing the temperature of the magnetic core to exceed the set temperature of the heat treatment furnace. However, this overshoot can be suppressed by a heat retention process. Overshoot causes variations in the permeability of the Fe-based nanocrystalline alloy magnetic core. Therefore, by suppressing overshoot, the temperature inside the magnetic core is made uniform, and as a result, variations in the permeability of the Fe-based nanocrystalline alloy magnetic core can be suppressed. Suppression of overshoot means that when a heat retention process is performed, the difference between the set temperature of the heat treatment furnace during nanocrystallization and the actual temperature of the magnetic core becomes smaller than when a heat retention process is not performed.

[0032] The inventors speculate that the reason why the heat retention process suppresses overshoot in nanocrystallization, and consequently suppresses variations in the permeability of the Fe-based nanocrystalline alloy magnetic core, is as follows: If overshoot occurs during the nanocrystallization of Fe-based alloys, the magnetic core may experience excessive precipitation of the crystalline phase due to temperatures exceeding the set temperature of the heat treatment furnace, potentially leading to variations in the permeability of the Fe-based nanocrystalline alloy magnetic core. However, performing a heat retention process before nanocrystallization suppresses the amount of thermal energy applied to the magnetic core material around which the Fe-based alloy ribbon is wound. This slows down the precipitation rate of the crystalline phase and suppresses self-heating associated with the precipitation of the crystalline phase. As a result, overshoot is suppressed, and consequently, variations in the permeability of the Fe-based nanocrystalline alloy magnetic core are expected to be reduced.

[0033] The heat treatment temperature in the heat retention process is not particularly limited as long as it is below the maximum temperature of the nanocrystallization process, and is usually 65°C lower or higher than the crystallization start temperature of the Fe-based alloy, preferably 60°C lower or higher, and usually 45°C lower or lower than the crystallization start temperature of the Fe-based alloy, preferably 40°C lower or lower. In other words, a suitable range for the heat treatment temperature is a range of 65°C lower or higher than the crystallization start temperature of the Fe-based alloy and 40°C lower or lower than the crystallization start temperature of the Fe-based alloy, and a range of 60°C lower or higher than the crystallization start temperature of the Fe-based alloy and 45°C lower or lower than the crystallization start temperature of the Fe-based alloy. The heat treatment time in the heat retention process depends on the heat treatment temperature in the heat retention process, the size of the magnetic core material, etc., but from the viewpoint of homogenizing the temperature inside the heat treatment furnace, it is usually 30 minutes or more, preferably 60 minutes or more, more preferably 100 minutes or more, and usually 5 hours or less, preferably 4 hours or less, more preferably 3 hours or less. In other words, suitable ranges for the heat treatment time include 30 minutes to 4 hours, 60 minutes to 5 hours, and 100 minutes to 3 hours. After the above heat treatment time has elapsed, i.e., after the heat retention process is completed, the temperature is raised to the maximum heat treatment temperature in the nanocrystallization process to allow the nanocrystallization of the Fe-based alloy to proceed sufficiently.

[0034] <1-3. Magnetic field application process> The manufacturing method according to this embodiment may further include a magnetic field application step in which a magnetic field is applied to the magnetic core material in the height direction while heat-treating the magnetic core material after the nanocrystallization step. From the viewpoint of improving the permeability of the Fe-based nanocrystalline alloy magnetic core in the high-frequency range, it is preferable to perform the magnetic field application step.

[0035] The maximum temperature of the heat treatment in the magnetic field application process is not particularly limited, but is usually 300°C or higher, preferably 400°C or higher, and is usually below the crystallization start temperature of the Fe-based alloy, preferably 50°C lower than the crystallization start temperature of the Fe-based alloy, and more preferably 60°C lower than the crystallization start temperature of the Fe-based alloy. In other words, preferred ranges for the maximum temperature of the heat treatment include 400°C or higher and below the crystallization start temperature of the Fe-based alloy, 300°C or higher and 50°C lower than the crystallization start temperature of the Fe-based alloy, and 400°C or higher and 60°C lower than the crystallization start temperature of the Fe-based alloy. The heating rate to reach the maximum temperature and the cooling rate after the maximum temperature has been maintained are not particularly limited, as long as they do not hinder the effects of the present invention, and rates generally used in heat treatment in the art of the present invention can be applied. The holding time at the above-mentioned maximum temperature depends on the above-mentioned maximum temperature, the size of the magnetic core material, etc., but from the viewpoint of homogenizing the temperature inside the heat treatment furnace, it is usually 20 minutes or more, preferably 30 minutes or more, and usually 5 hours or less, preferably 2 hours or less, and more preferably 1 hour or less. In other words, suitable ranges for the holding time at the above-mentioned maximum temperature include 20 minutes to 2 hours, 30 minutes to 5 hours, and 30 minutes to 1 hour.

[0036] In the magnetic field application process, the magnetic field is applied to the magnetic core material in the height direction of the magnetic core material, that is, in the width direction of the Fe-based alloy ribbon constituting the magnetic core material. The strength of the magnetic field applied to the magnetic core material is not particularly limited as long as it is high enough to magnetically saturate the magnetic core, and is usually 50 mT or more, preferably 80 mT or more, more preferably 100 mT or more, and also usually 150 mT or less. In other words, suitable ranges for magnetic field strength include 50 mT to 150 mT, 80 mT to 150 mT, and 100 mT to 150 mT.

[0037] The magnetic field application process may be carried out in an oxidizing atmosphere such as air, in an inert gas atmosphere such as argon, helium, or nitrogen, or under vacuum conditions, but it is preferable to carry it out in an inert gas atmosphere.

[0038] In the above description, the heat treatment in the oxide film formation step, the nanocrystallization step, and the magnetic field application step was described as including heating, holding at the maximum temperature, and cooling, but heating or cooling is not necessarily required. For example, after the heat treatment in the oxide film formation step, the atmosphere in the heat treatment furnace may be changed from an oxidizing atmosphere to a non-oxidizing atmosphere, and the nanocrystallization step may be performed by further heating. However, considering whether or not the atmosphere in the heat treatment furnace needs to be changed, whether or not a magnetic field needs to be applied, and the manufacturing equipment, it is preferable that the heat treatment in each step includes a series of operations: heating, holding at the maximum temperature, and cooling.

[0039] <2. Fe-based nanocrystalline alloy magnetic core> The Fe-based nanocrystalline alloy magnetic core according to the second embodiment of the present invention is a magnetic core formed by winding a ribbon, wherein the ribbon has, in this order, a first oxide film layer, a second oxide film layer, and a base material formed of an Fe-based nanocrystalline alloy containing an amorphous phase and crystalline grains, and the Fe-based nanocrystalline alloy has a composition represented by the following general formula (I). When a specific sample sampled from the Fe-based nanocrystalline alloy magnetic core according to this embodiment is analyzed by X-ray photoelectron spectroscopy (XPS), a characteristic depth profile described later is obtained.

[0040] Fex Si a B b Cu c Nb d (I) General formula (I) is the same as general formula (I) described in <1-1. Oxide Film Formation Process> above. Therefore, the definitions and preferred embodiments of a-d (atomic %) and x (atomic %) are as explained in <1-1. Oxide Film Formation Process>.

[0041] The Fe-based nanocrystalline alloy magnetic core according to this embodiment is a magnetic core obtained using an Fe-Si-B-Cu-Nb alloy having a composition represented by general formula (I) as the nanocrystallizable Fe-based alloy in the manufacturing method according to the first embodiment of the present invention, and exhibits high magnetic permeability in the low-frequency region. When manufacturing the Fe-based nanocrystalline alloy magnetic core according to this embodiment, it is not necessary to perform the magnetic field application step described in <1-3. Magnetic Field Application Step> above. This is because the application of a magnetic field does not affect the structure and composition of the oxide film described above, or only has a slight effect. However, since the Fe-based nanocrystalline alloy magnetic core exhibits high magnetic permeability in both the low-frequency and high-frequency regions when manufactured via the magnetic field application step, it is preferable that it be manufactured by a manufacturing method that includes a magnetic field application step.

[0042] <2-1. First oxide film layer, second oxide film layer, and base material> The Fe-based nanocrystalline alloy magnetic core according to this embodiment is manufactured by the manufacturing method according to the first embodiment of the present invention. Therefore, the ribbon constituting the magnetic core has, in this order, a first oxide film layer, a second oxide film layer, and a base material formed of an Fe-based nanocrystalline alloy containing an amorphous phase and crystalline grains. The first oxide film layer is the outermost layer of the ribbon. The first oxide film layer and the second oxide film layer are formed by the oxide film formation step in the above manufacturing method. The base material is formed by nanocrystallization of a nanocrystalline Fe-Si-B-Cu-Nb alloy having a composition represented by general formula (I) in the nanocrystallization step in the above manufacturing method. The base material may also contain components other than the Fe-based nanocrystalline alloy, such as components mixed in during the ribbon creation step and the oxide film formation step.

[0043] In this embodiment, the first oxide film layer and the second oxide film layer may be formed on at least one surface of the ribbon, but are usually formed on both surfaces of the ribbon. Furthermore, the first oxide film layer and the second oxide film layer may be formed on at least a portion of the ribbon's surface, but are usually formed over the entire surface of the ribbon.

[0044] The total thickness of the first oxide film layer and the second oxide film layer is not particularly limited, but since an oxide film with a thickness of approximately 4 nm is formed by natural oxidation, it is usually 5.0 nm or more, preferably 8.0 nm or more, more preferably 10 nm or more, and even more preferably 12 nm or more, and also usually 25 nm or less, preferably 20 nm or less. In other words, suitable ranges for the total thickness of the first oxide film layer and the second oxide film layer include the ranges of 5.0 nm to 20 nm, 8.0 nm to 20 nm, 10 nm to 25 nm, and 12 nm to 25 nm.

[0045] The presence or absence of the first and second oxide layers can be confirmed by transmission electron microscopy (TEM) observation of the ribbon cross-section. The thickness of the first and second oxide layers can also be measured from the TEM image. TEM imaging is performed to obtain a TEM image of the vicinity of the ribbon surface to be analyzed by XPS, in order to compare the TEM observation results of the first and second oxide layers with the results of XPS analysis. During TEM observation, a protective layer may be formed on the first oxide layer to improve the visibility of the first and second oxide layers in the TEM image. The protective layer can be formed by known methods, such as deposition. Materials such as carbon, platinum, and tungsten can be used for the protective layer. Furthermore, a sample for observing the ribbon cross-section can be prepared, for example, by cutting the ribbon using focused ion beam (FIB) spectroscopy. An example of TEM measurement conditions is shown below.

[0046] (TEM measurement conditions) • Equipment: JEM-2100 (manufactured by JEOL Ltd.) • Acceleration voltage: 200kV • Magnification: 100,000x or 200,000x

[0047] <2-2. Depth Profile obtained by XPS Analysis> When XPS analysis is performed on the surface structure of the Fe-based nanocrystalline alloy magnetic core according to this embodiment, including the first oxide film layer, the second oxide film layer, and the base material, a characteristic depth profile satisfying the following (A) and (B) is obtained.

[0048] (A) Cu in the depth range corresponding to the first oxide film layer 2p A peak appears. (B) In the depth range corresponding to the first oxide film layer, Cu 2p The peak intensity is due to O from SiO2. 1S It is stronger than [the other] strength.

[0049] As shown in the examples described later, in the depth profile of a conventional Fe-based nanocrystalline alloy magnetic core, Cu 2pThe peak (maximum value) is observed not in the depth range corresponding to the first oxide film layer (i.e., the outermost layer), but in the depth range corresponding to the space between the second oxide film layer and the base material. Therefore, conventional Fe-based nanocrystalline alloy magnetic cores do not satisfy (A) and (B). Consequently, the depth profile that satisfies (A) and (B) is unique to the Fe-based nanocrystalline alloy magnetic core according to this embodiment.

[0050] Furthermore, it is preferable that the Fe-based nanocrystalline alloy magnetic core according to this embodiment further satisfies the following conditions (C) and (D) in the depth profile obtained by XPS analysis. (C) O2 derived from SiO2 in the depth range corresponding to the second oxide film layer 1S and Si 2p A peak appears. (D) In ​​the depth range corresponding to the second oxide film layer, O derived from SiO2 1S The peak intensity of Cu 2p It is stronger than [the other] strength.

[0051] As shown in the examples described later, in the depth profile when an oxide film is formed on the ribbon surface by natural oxidation, the O2 is derived from SiO2. 1S and Si 2p The peak is observed in the depth range corresponding to the first oxide film layer. Therefore, in addition to (A) and (B), the depth profile satisfying (C) is also unique to the Fe-based nanocrystalline alloy magnetic core according to this embodiment.

[0052] Furthermore, it is preferable that the Fe-based nanocrystalline alloy magnetic core according to this embodiment further satisfies the following (E) in the depth profile obtained by XPS analysis. (E) Cu in the depth range corresponding to the first oxide film layer 2p The peak intensity corresponds to the depth range of Cu in the base material. 2p It is stronger than [the other] strength.

[0053] As shown in the examples described later, in the depth profile of a conventional Fe-based nanocrystalline alloy magnetic core, the depth range corresponding to the first oxide film layer is Cu 2pNo peak (maximum value) appeared, indicating weak Cu intensity. 2p The following signal is observed. In addition, in the depth range corresponding to the base material, Cu is stronger than in the depth range corresponding to the first oxide film layer. 2p The signal is observed. Therefore, the depth profile satisfying (E) is also unique to the Fe-based nanocrystalline alloy magnetic core according to this embodiment.

[0054] In this specification, the depth ranges corresponding to the first oxide layer and the second oxide layer are ranges based on the thickness of the first oxide layer and the second oxide layer measured from TEM images, respectively. 2p In terms of strength, Cu at a depth where the effect of the oxide film is not observed. 2p The strength of the following will be adopted. More specifically, Cu within a depth range of 5 nm 2p Cu for maximum strength 2p A depth range with small fluctuations in signal intensity is selected such that the ratio of the minimum intensity is usually 0.80 or higher, preferably 0.85 or higher, and more preferably 0.90 or higher, and within this depth range Cu 2p The strength of the Cu in the depth range corresponding to the base material 2p The intensity is assumed to be such that the signal intensity fluctuations are small. Examples of depth ranges where such fluctuations in signal intensity are small include the range of 15 nm or more in Example 2, the range of 28 nm or more in Comparative Example 2, and the range of 21 nm or more in Comparative Example 4 (ranges indicated by arrows in Figures 5 to 7).

[0055] In this embodiment, the specific sample subjected to XPS analysis is sample X, as shown below. (Sample X) When the space between the inner and outer surfaces of the Fe-based nanocrystalline alloy magnetic core is virtually divided into three regions—the first region, the second region, and the third region—from the inner surface toward the outer surface, a ribbon located within the second region is cut out and used as the sample. The first, second, and third regions are regions that divide the radial length between the inner and outer surfaces into 40 / 20 / 40. X-ray photoelectron spectroscopy analysis is performed on the surface of the sample that was facing the outer surface when it was wound to form the Fe-based nanocrystalline alloy magnetic core.

[0056] The reason for using ribbons located within the second region as samples is as follows: In a magnetic core formed by winding ribbons, the permeability is influenced by the oxide film layer formed on the surface of the ribbon located near the midpoint between the inner and outer surfaces of the magnetic core in the radial direction, or on the ribbon located slightly closer to the inner surface than the midpoint. Furthermore, the oxide film layer formed on the surface of the ribbon located on the outer surface side of the magnetic core in the radial direction may be affected by the ambient environment during the manufacturing process of the magnetic core. Therefore, a specific oxide film layer can be stably formed regardless of the ambient environment only on the surface of the ribbon located near the midpoint in the radial direction of the magnetic core, or on the ribbon located slightly closer to the inner surface than the midpoint. Accordingly, in order to evaluate the structure of the oxide film that contributes to improving the permeability, it is necessary to analyze the oxide film layer formed on the surface of the ribbon located near the midpoint between the inner and outer surfaces, or on the ribbon located slightly closer to the inner surface than the midpoint.

[0057] The sample X for XPS analysis will be described in more detail with reference to Figure 3. Figure 3(a) is a perspective view of the Fe-based nanocrystalline alloy magnetic core, and Figure 3(b) is a cross-sectional perspective view of the Fe-based nanocrystalline alloy magnetic core. As shown in Figure 3(a), the Fe-based nanocrystalline alloy magnetic core 10 according to this embodiment is a magnetic core formed by winding a ribbon in a toroidal shape. The ribbon is stacked between the inner circumferential surface 11 and the outer circumferential surface 12 of the Fe-based nanocrystalline alloy magnetic core 10 by winding. Here, as shown in Figure 3(b), the radial length between the inner circumferential surface 11 and the outer circumferential surface 12 of the Fe-based nanocrystalline alloy magnetic core 10 is virtually divided into three regions, which are designated as the first region 21, the second region 22, and the third region 23, in order from the inner circumferential surface 11 to the outer circumferential surface 12. The first region 21, the second region 22, and the third region 23 are regions that divide the radial length between the inner circumferential surface 11 and the outer circumferential surface 12 into l1 / l2 / l3. l1 / l2 / l3 are usually 40 / 20 / 40, but may also be 40 / 15 / 45 or 45 / 10 / 45. XPS analysis is performed by cutting out the ribbon located in the central part between the inner circumferential surface 11 and the outer circumferential surface 12 of the second region 22, and analyzing the surface of the ribbon that was facing the outer circumferential surface 12 when it was wound. In XPS analysis, the photoelectron intensity is measured at different depths from the ribbon surface while sputtering the analysis surface. An example of the conditions for XPS analysis is shown below.

[0058] (XPS analysis conditions) • Equipment: PHI5000VersaProbe (manufactured by ULVAC-PHI, Inc.) ·Achieved vacuum level: 6.7×10 -8 Pa or less • Excitation source: Monochromatic Al-Kα X-ray Output: 25W • Detection area: 100 μmφ ·Incidence angle: 45° • Extraction angle: 45° (Spatter conditions) • Ion species: Argon • Acceleration voltage: 1kV ·Sweep area: 2mm x 2mm • Sputtering rate: 2.27 nm / min

[0059] In XPS analysis, a depth profile is obtained by creating a chart with the depth (nm) in SiO2 equivalent, calculated using the sputter etching rate of an SiO2 standard sample from the sputtering time, on the horizontal axis and the photoelectron intensity (cps) on the vertical axis, and determining whether or not the above conditions (A) to (E) are met.

[0060] <3. Applications of Fe-based nanocrystalline alloy magnetic cores> The Fe-based nanocrystalline alloy magnetic core produced by the manufacturing method according to the first embodiment of the present invention and the Fe-based nanocrystalline alloy magnetic core according to the second embodiment of the present invention can be suitably used as a magnetic core for reactors, common mode choke coils, transformers, communication pulse transformers, motors, or generators. [Examples]

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the essence of the invention.

[0062] <Example 1> An Fe-based alloy ribbon, 12.5 mm wide and 14 μm thick, made of an Fe-Si-B-Cu-Nb alloy having the composition represented by the above general formula (I), was wound to create an Fe-based alloy magnetic core with an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 12.5 mm. The crystallization start temperature of the Fe-based alloy constituting the Fe-based alloy ribbon was determined to be 516°C by differential scanning calorimeter (DSC) measurement.

[0063] (Oxide film formation process) An oxide film was formed by placing an Fe-based alloy core material in a heat treatment furnace and heating it at a maximum temperature of 440°C for 180 minutes under an oxidizing atmosphere with an oxygen concentration of 0.4 vol%.

[0064] (Nanocrystallization process) The Fe-based alloy core material, after the oxide film formation process, was placed in a heat treatment furnace and heated at 470°C for 120 minutes under a nitrogen atmosphere (oxygen concentration 0 vol%), followed by heating at 550°C for 100 minutes to induce nanocrystallization of the Fe-based alloy. The Fe-based nanocrystalline alloy core material of Example 1 was obtained by cooling the nanocrystallized core material to room temperature (20°C).

[0065] <Example 2> (Magnetic field application process) The Fe-based nanocrystalline alloy core obtained in Example 1 was placed in a heat treatment furnace and heat-treated under a nitrogen atmosphere (oxygen concentration 0 vol%) while a magnetic field of strength 100 mT was applied to the core in the direction of its height. After the magnetic field was applied, the core was cooled to room temperature (20°C) to obtain an Fe-based nanocrystalline alloy core. The heat treatment was carried out under conditions where the maximum temperature was 450°C and the holding time was 30 minutes.

[0066] <Comparative Example 1> An Fe-based nanocrystalline alloy magnetic core was obtained in the same manner as in Example 1, except that the oxide film formation step was omitted and the nanocrystallization step was carried out in an oxidizing atmosphere with an oxygen concentration of 0.4 vol%.

[0067] <Comparative Example 2> An Fe-based nanocrystalline alloy magnetic core was obtained in the same manner as in Example 2, except that the oxide film formation step was omitted and the nanocrystallization step was carried out in an oxidizing atmosphere with an oxygen concentration of 0.4 vol%.

[0068] <Comparative Example 3> An Fe-based nanocrystalline alloy magnetic core was obtained in the same manner as in Example 1, except that the oxide film formation step was omitted.

[0069] <Comparative Example 4> An Fe-based nanocrystalline alloy magnetic core was obtained in the same manner as in Example 2, except that the oxide film formation step was omitted.

[0070] [Evaluation of relative permeability] The Fe-based nanocrystalline alloy magnetic cores obtained in the examples and comparative examples were loaded into a resin case to create a hollow core. A coated copper wire with a diameter of 0.5 mm was passed through the hollow portion of the created core to create a single-turn core. Using an impedance analyzer (Agilent Technologies, 4294A), the inductance of the obtained core was measured at frequencies of 10 kHz and 100 kHz, and the relative permeability of the Fe-based nanocrystalline alloy magnetic core was calculated based on the following formula (1). The magnetic path length l was 6.3 × 10⁻⁶. -2 m, effective cross-sectional area A is 4.8 × 10 -5 m 2 The number of turns N was set to 1. The results are shown in Table 1, Figure 1, and Figure 2.

[0071] μr = μ / μ0 (1) μr: relative permeability μ0: Permeability of vacuum = 4π × 10 -7 [H / m] μ: Magnetic permeability [H / m]=Ll / A / N 2 L: Inductance [H] l:Magnetic path length [m]=6.3×10 -2 [m] A: Core effective cross-sectional area [m²] 2 ] = 4.8 × 10 -5 [m 2 ] N: Number of turns = 1

[0072] [Table 1]

[0073] Table 1 and Figure 1 show that the Fe-based nanocrystalline alloy magnetic core obtained by simultaneously carrying out oxide film formation and nanocrystallization (Comparative Example 1) had a lower relative permeability at a frequency of 10 kHz than the Fe-based nanocrystalline alloy magnetic core obtained by performing nanocrystallization only without oxide film formation (Comparative Example 3). This confirms that the formation of an oxide film reduces the permeability of the Fe-based nanocrystalline alloy magnetic core in the low-frequency region. On the other hand, the Fe-based nanocrystalline alloy magnetic core (Example 1), obtained by forming an oxide film under conditions that do not cause nanocrystallization, and then performing nanocrystallization in a non-oxidizing atmosphere where no oxide film is formed, had an oxide film similar to the Fe-based nanocrystalline alloy magnetic core obtained in Comparative Example 1. However, despite having an oxide film, the relative permeability at a frequency of 10 kHz was significantly improved and was higher than that of the Fe-based nanocrystalline alloy magnetic core obtained in Comparative Example 3. These results demonstrate that, contrary to common technical knowledge, performing oxide film formation and nanocrystallization separately in this order improves the permeability of the Fe-based nanocrystalline alloy magnetic core in the low-frequency region, as oxide film formation reduces the permeability of the nanocrystalline alloy magnetic core in the low-frequency region. Furthermore, as shown in Table 1 and Figure 1, it was confirmed that applying a magnetic field also improves the permeability of the Fe-based nanocrystalline alloy magnetic core in the low-frequency region.

[0074] As shown in Table 1 and Figure 2, the relative permeability at a frequency of 100 kHz of the Fe-based nanocrystalline alloy magnetic core (Example 2), obtained by sequentially performing oxide film formation, nanocrystallization, and magnetic field application, was as high as that of the Fe-based nanocrystalline alloy magnetic core (Comparative Example 2), obtained by applying a magnetic field to a magnetic core material prepared by simultaneously performing oxide film formation and nanocrystallization. These results indicate that by applying a magnetic field, it is possible to manufacture Fe-based nanocrystalline alloy magnetic cores that exhibit high magnetic permeability even in the high-frequency range.

[0075] [TEM observation] Ribbons were cut from the Fe-based nanocrystalline alloy magnetic cores obtained in Example 2, Comparative Example 2, and Comparative Example 4 under the same conditions as sample X for XPS analysis (however, l1 / l2 / l3 = 45 / 10 / 45). Next, a protective layer was formed on the surface of the ribbon that was under the same conditions as the analysis surface for XPS analysis, using a deposition method. A sample for TEM observation was obtained by cutting the ribbon coated with this protective layer perpendicular to the surface. TEM measurements were performed on the obtained TEM observation sample under the following measurement conditions. The obtained TEM image is shown in Figure 4.

[0076] (TEM measurement conditions) • Equipment: JEM-2100 (manufactured by JEOL Ltd.) • Acceleration voltage: 200kV • Magnification: 100,000x (Example 2, Comparative Example 4) or 200,000x (Comparative Example 2)

[0077] Figure 4 shows that the Fe-based nanocrystalline alloy magnetic cores obtained in Example 2, Comparative Example 2, and Comparative Example 4 all have two oxide film layers on the ribbon surface. The thickness of each oxide film layer measured from Figure 4 is shown in Table 2.

[0078] [Table 2]

[0079] Figure 4 and Table 2 show that in Example 2, where an oxide film was formed prior to nanocrystallization and then nanocrystallization was performed under a non-oxidizing atmosphere, the first oxide film layer and the second oxide film layer had similar thicknesses. In contrast, in Comparative Example 2, where an oxide film was formed while nanocrystallization was performed, and in Comparative Example 4, where the oxide film formation step was omitted and nanocrystallization was also performed under a non-oxidizing atmosphere, the first oxide film layer was more than twice as thick as the second oxide film layer.

[0080] In Comparative Example 4, since no oxide film was intentionally formed, the oxide film layer formed on the ribbon surface was due to natural oxidation. Therefore, the total thickness of the two oxide film layers in Comparative Example 4 was less than 5 nm, which was significantly thinner than the total thickness of the first and second oxide film layers in Example 2, where an oxide film was intentionally formed.

[0081] [Measuring depth profiles using XPS analysis] From the Fe-based nanocrystalline alloy magnetic cores obtained in Example 2, Comparative Example 2, and Comparative Example 4, a ribbon located within the second region (l1 / l2 / l3 = 45 / 10 / 45) was cut out and designated as sample X. Of the two surfaces of sample X, the surface that faced the outer circumferential surface when it was wound to form the magnetic core was designated as the analysis surface, and a depth profile was obtained by performing XPS analysis while sputtering this analysis surface. The XPS analysis conditions are as follows. The results are shown in Figures 5 to 7. In Figures 5 to 7, the horizontal axis of the XPS analysis chart represents the depth (nm) in SiO2 equivalent, calculated using the sputter etching rate of an SiO2 standard sample from the sputtering time.

[0082] (XPS analysis conditions) • Equipment: PHI5000VersaProbe (manufactured by ULVAC-PHI, Inc.) ·Achieved vacuum level: 6.7×10 -8 Pa or less • Excitation source: Monochromatic Al-Kα X-ray Output: 25W • Detection area: 100 μmφ ·Incidence angle: 45° • Extraction angle: 45° (Spatter conditions) • Ion species: Argon • Acceleration voltage: 1kV ·Sweep area: 2mm x 2mm • Sputtering rate: 2.27 nm / min

[0083] As can be seen from Figure 5, in the depth profile of Example 2, Cu is present at a depth of approximately 2.27 nm, which corresponds to the first oxide film layer. 2p A peak (maximum value) was observed, and in the depth range corresponding to the first oxide film layer, Cu 2p The peak intensity is due to SiO2 1S It was found to be stronger than the strength of [another component]. In addition, in the depth profile of Example 2, O derived from SiO2 was found at a depth of around 11.35 nm, which corresponds to the second oxide film layer. 1S and Si 2p A peak was observed, indicating that in the depth range corresponding to the second oxide film layer, O originated from SiO2. 1SThe peak intensity of Cu 2p It was found to be stronger than the strength of the first oxide film layer. Furthermore, Cu in the depth range corresponding to the first oxide film layer 2p The peak intensity is measured in the Cu depth range corresponding to the base material. 2p It was stronger than the strength of [the other thing].

[0084] On the other hand, in the depth profiles of Comparative Example 2 and Comparative Example 4, Cu 2p The strength of the O2 was maximum in the depth range corresponding to the space between the second oxide film layer and the base material, weak in the depth range corresponding to the base material, and even weaker in the depth range corresponding to the first oxide film layer. In addition, in the depth profile of Comparative Example 2, O2 derived from SiO2 was present around 9.08 nm at a depth corresponding to the second oxide film layer. 1S and Si 2p A peak was observed, but in the depth profile of Comparative Example 4, O originated from SiO2. 1S and Si 2p The peak was observed at a depth of approximately 2.27 nm, corresponding to the first oxide film layer. [Explanation of Symbols]

[0085] 10 Fe-based nanocrystalline alloy magnetic core 11 Inner surface 12 Outer surface 21 First area 22 Second area 23 Third area

Claims

1. An oxide film formation process in which a magnetic core material, which consists of a ribbon of nanocrystallizable Fe-based alloy wound around it, is heat-treated in an oxidizing atmosphere, and The process includes a nanocrystallization step in which the Fe-based alloy capable of nanocrystallization is nanocrystallized by heat-treating the magnetic core material after the oxide film formation step in a non-oxidizing atmosphere. The maximum temperature of the heat treatment in the oxide film formation step is below the crystallization start temperature of the nanocrystallizable Fe-based alloy. A method for manufacturing an Fe-based nanocrystalline alloy magnetic core, wherein the maximum temperature of the heat treatment in the nanocrystallization step is a temperature equal to or greater than the crystallization initiation temperature of the Fe-based alloy that can be nanocrystallized.

2. The process includes a magnetic field application step in which a magnetic field is applied to the magnetic core material in the height direction while heat treatment is applied to the magnetic core material after the nanocrystallization step, The method for producing an Fe-based nanocrystalline alloy magnetic core according to claim 1, wherein the maximum temperature of the heat treatment in the magnetic field application step is below the crystallization start temperature of the nanocrystalline Fe-based alloy.

3. A method for producing an Fe-based nanocrystalline alloy magnetic core according to claim 1 or 2, wherein the nanocrystallizable Fe-based alloy has a composition represented by the following general formula (I). Fe ｘ Si ａ B ｂ Cu ｃ Nb ｄ (I) (In general formula (I), a to d (atomic %) represent 3.0 ≤ a ≤ 12.0, 1.0 ≤ b ≤ 7.0, 1.0 ≤ c ≤ 5.0, and 1.0 ≤ d ≤ 9.0, respectively; x (atomic %) is the remainder other than Si, B, Cu, and Nb, satisfying 73.0 ≤ x ≤ 92.0.)

4. It is a magnetic core made by winding a ribbon, The ribbon has, in this order, a first oxide film layer, a second oxide film layer, and a base material formed of an Fe-based nanocrystalline alloy containing an amorphous phase and crystalline grains. The Fe-based nanocrystalline alloy has a composition represented by the following general formula (I), A Fe-based nanocrystalline alloy magnetic core that satisfies the following conditions (A) and (B) in the depth profile obtained by X-ray photoelectron spectroscopy of sample X below. Fe ｘ Si ａ B ｂ Cu ｃ Nb ｄ (I) (In general formula (I), a to d (atomic %) represent 3.0 ≤ a ≤ 12.0, 1.0 ≤ b ≤ 7.0, 1.0 ≤ c ≤ 5.0, and 1.0 ≤ d ≤ 9.0, respectively; x (atomic %) is the remainder other than Si, B, Cu, and Nb, satisfying 73.0 ≤ x ≤ 92.0.) (A) Cu in the depth range corresponding to the first oxide film layer ２ｐ A peak appears. (B) In the depth range corresponding to the first oxide film layer, Cu ２ｐ The peak intensity is SiO ２ Origin of O １Ｓ It is stronger than [the other] strength. (Sample X) When the space between the inner and outer surfaces of the Fe-based nanocrystalline alloy magnetic core is virtually divided into three regions, a first region, a second region, and a third region, from the inner surface toward the outer surface, a ribbon located within the second region is cut out to be used as the sample. The first, second, and third regions are regions that divide the radial length between the inner and outer surfaces into 40 / 20 / 40 parts. X-ray photoelectron spectroscopy is performed on the surface of the sample that was facing the outer surface when it was wound to form the Fe-based nanocrystalline alloy magnetic core.

5. The Fe-based nanocrystalline alloy magnetic core according to claim 4, wherein the depth profile further satisfies (C) and (D) below. (C) SiO in the depth range corresponding to the second oxide film layer ２ Origin of O １Ｓ and Si ２ｐ A peak appears. (D) In ​​the depth range corresponding to the second oxide film layer, SiO ２ Origin of O １Ｓ The peak intensity of Cu ２ｐ It is stronger than [the other] strength.

6. The Fe-based nanocrystalline alloy magnetic core according to claim 4 or 5, wherein the depth profile further satisfies (E) below. (E) Cu in the depth range corresponding to the first oxide film layer ２ｐ The peak intensity corresponds to the Cu in the depth range corresponding to the base material. ２ｐ It is stronger than [the other] strength.

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