JP7119979B2 - Composite magnetic material and magnetic core - Google Patents

Description

The present invention relates to composite magnetic materials and magnetic cores.

2. Description of the Related Art In recent years, the frequency band used by wireless communication devices such as mobile phones and personal digital assistants has been increasing, and the used wireless signal frequency is in the GHz band. Therefore, by applying a magnetic material with a relatively high magnetic permeability even in the high frequency region of the GHz band to electronic parts used in such a high frequency region of the GHz band, it is possible to improve the filter characteristics and reduce the size of the antenna. Attempts are being made to improve It is also desired to reduce the magnetic loss in the high frequency region. Among them, attempts have been made to increase the aspect ratio of the magnetic material used for the magnetic core.

For example, Patent Document 1 describes a composite material using FeSiAl-based acicular powder and spherical powder. Patent Document 2 describes a composite material using amorphous acicular powder and spherical powder.

However, at present, there is a demand for a magnetic core with a higher relative permeability μr and a lower magnetic loss tan δ.

JP-A-11-260617 Japanese Patent Application Laid-Open No. 2002-105502

SUMMARY OF THE INVENTION An object of the present invention is to provide a composite magnetic material and a magnetic core that are used for a magnetic core having a high relative magnetic permeability μr and a low magnetic loss tan δ in the high frequency region of the GHz band.

In order to achieve the above object, the composite magnetic material of the present invention
A composite magnetic material containing acicular powder and resin,
The acicular powder is mainly composed of Fe or Fe and Co,
The primary particles of the acicular powder have an average minor axis length of 100 nm or less,
In the frequency distribution of the aspect ratios of the primary particles of the acicular powder, the aspect ratio of the first peak with the highest frequency and the aspect ratio of the second peak with the second highest frequency are in the range of 3.0 or more and 10 or less. can be,
(aspect ratio of first peak) / (aspect ratio of second peak) and (aspect ratio of second peak) / (aspect ratio of first peak), whichever is smaller is 0.30 or more and 0.80 or less It is characterized by

The composite magnetic material of the present invention has the above-described average minor axis length and aspect ratio frequency distribution, and is used for magnetic cores with high relative permeability μr and low magnetic loss tan δ in the high-frequency region of the GHz band. becomes.

In the acicular powder, it is preferable that the content ratio of Co to the main component is 0 to 40 atom % (not including 0 atom %).

A magnetic core of the present invention includes the composite magnetic material described above.

4 is a drawing showing major axis length and minor axis length in a composite magnetic material. It is an example of a histogram for explaining the procedure for determining peaks. 14 is a histogram showing the frequency distribution of aspect ratios of Example 8. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described based on embodiments shown in the drawings.

The magnetic core (core) of this embodiment is made of a composite magnetic material containing acicular powder and resin.

The acicular powder is composed of a soft magnetic material containing Fe or Fe and Co as main components. The average minor axis length of the primary particles of the acicular powder is 100 nm or less. When the average minor axis length is 100 nm or less, the magnetic loss (tan δ) of the magnetic core can be reduced. There is no particular lower limit to the average minor axis length of the primary particles of the acicular powder. For example, the primary particles of the acicular powder may have an average minor axis length of 15 nm or more.

When the average minor axis length exceeds 100 nm, the magnetic loss of the magnetic core increases because double magnetic domains are likely to occur in the primary particles, resulting in increased eddy current loss.

Moreover, the shape of the acicular powder is not particularly limited. It may be acicular, pseudoacicular, spheroidal, or pseudospheroidal.

The minor axis length, major axis length and aspect ratio of the primary particles of the acicular powder are calculated by the following methods.

First, using a SEM, TEM, or the like, a two-dimensional image of the acicular powder 1 whose major axis length, minor axis length and aspect ratio are to be measured is taken. On the photographed two-dimensional image, as shown in FIG. 1, an ellipse 1a circumscribing the acicular powder 1 is drawn. Shaft length. The aspect ratio is L1/L2.

The composite magnetic material according to this embodiment has the first peak with the highest frequency and the second peak with the second highest frequency in the frequency distribution of the aspect ratio of the primary particles of the acicular powder. That is, the primary particles of the acicular powder have at least two peaks in the aspect ratio frequency distribution.

And the aspect-ratio of a 1st peak and the aspect-ratio of a 2nd peak exist in the range of 3-10, respectively. The presence of two peaks with high frequency in the aspect ratio range of 3.0 or more and 10 or less makes it easier to increase the filling factor, which will be described later, compared to the case where only one peak exists. Then, the relative magnetic permeability μr can be improved.

If the aspect ratio of the first peak or the second peak exceeds 10, the effect of improving the relative magnetic permeability μr cannot be obtained.

Furthermore, the smaller of (aspect ratio of the first peak) / (aspect ratio of the second peak) and (aspect ratio of the second peak) / (aspect ratio of the first peak) is 0.30 or more and 0.80 or less is. That is, it is necessary that the aspect ratio between the first peak and the second peak is open to some extent. Since the aspect ratio is widened to some extent between the first peak and the second peak, it becomes easier to increase the filling factor and to improve the relative permeability μr.

Hereinafter, the smaller of (aspect ratio of first peak) / (aspect ratio of second peak) and (aspect ratio of second peak) / (aspect ratio of first peak) is simply referred to as "ratio of aspect ratio" I may call

The smaller the aspect ratio, the easier it is to increase the filling rate. On the other hand, if the aspect ratio is too large, it becomes difficult to increase the filling rate, and it becomes difficult to improve the relative magnetic permeability μr.

A method of determining a peak in the frequency distribution of aspect ratios will be described below with reference to the drawings.

First, the aspect ratio of primary particles of 500 or more acicular powder is measured. Next, as shown in FIG. 2, a histogram is created with the width of each class set to 0.25.

Next, it is assumed that a class having a higher frequency than any adjacent class is detected and has a provisional peak at the median value of the class having a higher frequency than any adjacent class.

Moreover, when the frequencies of two or more adjacent classes are the same, these two or more classes are regarded as a single class group. The frequency of the class group concerned shall be the same as the frequency of each class constituting the class group concerned. Then, it is assumed that there is a provisional peak at the median of the class group that has a higher frequency than any adjacent classes.

Then, each provisional peak is sorted in descending order of frequency.

Next, the frequency of the class two adjacent to the class (class group) having the provisional peak is examined. If the frequencies of the two adjacent classes are both lower than the frequency of a class (class group) having a provisional peak, the provisional peak is formally defined as a peak. Then, each peak is designated as a first peak, a second peak, . . . in descending order of frequency.

The procedure for determining the first peak, the second peak, . . . in the histogram of FIG. 2 will be described below.

First, the temporary peak in the histogram of FIG. 2 is determined. In the histogram of FIG. 2, provisional peaks A to I are present. Note that each provisional peak has a high frequency in ABC order.

Then, it is checked whether each provisional peak is formally regarded as a peak.

The frequency of the class with provisional peak A is higher than the frequency of any two neighboring classes. Therefore, the provisional peak A becomes the first peak.

The frequency of the class having the provisional peak B is lower than the frequency of the next class (the class having the provisional peak A) in the negative aspect ratio direction. Therefore, provisional peak B is not the second peak.

The frequency of the class having the provisional peak C is lower than the frequency of the class (the class having the provisional peak A) two adjacent in the positive aspect ratio direction. Therefore, provisional peak C is not the second peak.

The frequency of the class group with provisional peak D is higher than the frequency of any two neighboring classes. Therefore, provisional peak D is the second peak.

The frequency of the class having the provisional peak E is lower than the frequency of the class (the class included in the class group having the provisional peak D) whose aspect ratio is two adjacent in the positive direction. Therefore, provisional peak E is not the third peak.

The frequency of the class having the provisional peak F is lower than the frequency of the class (the class included in the class group having the provisional peak D) whose aspect ratio is two adjacent in the negative direction. Therefore, provisional peak F is not the third peak.

The frequency of the class having the provisional peak G is lower than the frequency of the class (the class having the provisional peak F) two adjacent in the negative aspect ratio direction. Therefore, provisional peak G is not the third peak.

The frequency of the class with provisional peak H is higher than the frequency of any two neighboring classes. Therefore, provisional peak H is the third peak.

The frequency of the class with interim peak I is higher than the frequency of any two neighboring classes. Therefore, provisional peak I is the fourth peak.

As described above, the histogram in FIG. 2 has four peaks from the first peak to the fourth peak. The aspect ratio of the first peak is 2.125, the aspect ratio of the second peak is 4.25, the aspect ratio of the third peak is 6.875, and the aspect ratio of the fourth peak is 8.125.

Furthermore, the aspect ratio ratio is 2.125/4.25=0.5.

Further, the acicular powder contains Fe or Fe and Co as main components. Here, "containing as a main component" means that the content ratio of Fe or Fe and Co to the entire acicular powder is 50 atom % or more.

Furthermore, the content of Co with respect to the total content of Fe and Co, which are the main components, is preferably 0 to 40 atom % (excluding 0 atom %), more preferably 15 to 25 atom %. When the acicular powder contains Fe and Co as main components, the effect of increasing the relative magnetic permeability μr is further enhanced.

In addition, the acicular powder contains elements other than the main components, such as V, Cr, Mn, Cu, Zn, Ni, Mg, Ca, Sr, Ba, rare earth elements, Ti, Zr, Hf, Nb, Ta, Zn, and Al. , Ga and Si may be included, and in particular Al, Si and/or Ni may be included to improve oxidation resistance. The content of other elements is not particularly limited, but is preferably 5% by mass or less in total with respect to the entire acicular powder.

Also, the acicular powder may be coated with an oxide layer. There are no particular restrictions on the type of oxide forming the oxide layer and the thickness of the oxide layer. For example, it may be an oxide containing one or more non-magnetic metals selected from Mg, Ca, Sr, Ba, rare earth elements, Ti, Zr, Hf, Nb, Ta, Zn, Al, Ga and Si. The thickness of the oxide layer may be, for example, 1.0 nm or more and 10.0 nm or less, or 1.0 nm or more and 5.0 nm or less. By covering the acicular powder with an oxide layer, it becomes easier to prevent the acicular powder from being oxidized.

The acicular powder is further coated with resin. That is, the composite magnetic material according to this embodiment has a resin. The type of resin is not particularly limited. Examples include epoxy resin, phenol resin, and acrylic resin. By coating with resin, it is possible to improve the insulation, suppress the occurrence of eddy currents between powders that suppress magnetization rotation, which will be described later, and easily improve the relative permeability μr.

The reason why the relative magnetic permeability μr of the magnetic core containing acicular powder having the above-mentioned first and second peaks in the aspect ratio frequency distribution, particularly in the high frequency region, is improved is considered as follows.

In particular, the magnitude of magnetization that appears in the high-frequency region is considered to strongly depend on the magnitude of displacement of precession of magnetization inside the acicular powder. The greater the precession displacement, the greater the magnetization that appears and the higher the magnetic permeability.

Here, when an acicular powder having a large shape anisotropy, that is, an acicular powder having a large aspect ratio is used, a single domain structure is more easily self-organized by a demagnetizing field when an external magnetic field is applied.

As a result, when acicular powder having only one peak in the frequency distribution of aspect ratios is used, the precession of magnetization is suppressed as the aspect ratio at the peak increases, and the relative magnetic permeability μr tends to decrease. However, since the internal structure is uniform due to self-organization, the effective magnetization is increased and the frequency characteristics are increased.

On the other hand, the smaller the aspect ratio at the peak, the greater the precession of magnetization and the higher the relative magnetic permeability μr. However, since self-organization is difficult and the internal structure is non-uniform, the effective magnetization is reduced and the frequency characteristics are lowered.

Here, when the frequency distribution of aspect ratios has two peaks with high frequency and the ratio of aspect ratios is 0.80 or less, acicular powder with a large aspect ratio is preferentially self-organized. At this time, an exchange interaction occurs between the acicular powders, and the acicular powders with a small aspect ratio tend to self-organize in the same direction as the acicular powders with a large aspect ratio. Therefore, starting from the self-organization of the acicular powder with a large aspect ratio, the internal structure of the acicular powder with a small aspect ratio is also homogenized, increasing the effective magnetization. Then, the frequency characteristic becomes higher.

Conversely, acicular powder with a small aspect ratio has increased precession. At this time, an exchange interaction occurs between the acicular powder, and the precession of the acicular powder having a large aspect ratio tends to increase. Therefore, the precession of the acicular powder with a large aspect ratio also increases with the precession of the acicular powder with a small aspect ratio as a starting point. Then, the relative magnetic permeability μr increases.

From the above, when the frequency distribution of the aspect ratio has two peaks with high frequency, the aspect ratio of each peak is 3.0 or more and 10 or less, and the ratio of the aspect ratio is 0.80 or less, A high frequency characteristic and an increase in the relative magnetic permeability μr are achieved at the same time.

If the aspect ratio of the peak with high frequency exceeds 10, the density of the magnetic core produced using the magnetic powder is lowered, and the relative magnetic permeability μr is lowered. If the aspect ratio of the frequently-frequent peaks is less than 3.0, the magnetic loss tan δ increases especially in the high frequency range of 3 GHz or higher.

The magnetic core according to the present embodiment may contain the composite magnetic material described above. Also, the type of the magnetic core is not particularly limited, and for example, a dust core may be used. Further, for example, a dust core in which a coil is embedded may contain the composite magnetic material.

Moreover, it is preferable that the content ratio of the acicular powder (hereinafter also referred to as the filling rate) with respect to the entire magnetic core is 25 vol % or more. By sufficiently increasing the filling rate, the relative magnetic permeability μr can be sufficiently improved.

Here, there is no particular limitation on the method of calculating the filling rate. For example, the method shown below is mentioned.

First, a cross section obtained by cutting a magnetic core is polished to prepare an observation surface. Next, the observation surface is observed using an electron microscope (SEM). At this time, the observed image may be binarized by removing noise. Then, the area ratio of acicular powder to the area of the entire observation surface is calculated. In this embodiment, the area ratio and the filling rate are considered to be equal, and the area ratio is taken as the filling rate.

In addition, in calculating the filling rate, the observation surface has a size that includes a total of 1000 or more particles of the acicular powder. It should be noted that there may be a plurality of viewing surfaces, and the size may include 1000 particles or more in total.

A method for manufacturing the composite magnetic material and the magnetic core according to this embodiment will be described below, but the method for manufacturing the composite magnetic material and the magnetic core according to this embodiment is not limited to the following methods.

First, an acicular powder made of a soft magnetic material whose main component is Fe or Fe and Co is produced. Here, for example, by preparing a plurality of types of acicular powder having different average aspect ratios, the finally obtained composite magnetic material can contain acicular powder having a predetermined frequency distribution of aspect ratios. There is no particular limitation on the method for producing the acicular powder, and a method commonly used in this technical field can be used. For example, it may be prepared by a known method of heating and reducing a raw material powder composed of a compound such as α-FeOOH, FeO or CoO. By controlling the content of Fe, Co and/or other elements in the raw material powder, the composition of the obtained acicular powder can be controlled.

Here, by controlling the average minor axis length and average aspect ratio of the raw material powder, the average minor axis length, average major axis length and average aspect ratio of the acicular powder can be controlled. The method for controlling the average short axis length, average long axis length and average aspect ratio of acicular powder is not limited to the above methods.

In the case of coating the acicular powder with the oxide layer of the non-magnetic metal, a method of adding the non-magnetic metal to the raw material powder and then subjecting it to thermal reduction is exemplified. There is no particular limitation on the method of adding the non-magnetic metal to the raw material powder. For example, a method of mixing a raw material powder with a solution containing a non-metallic element, adjusting the pH, filtering and drying the mixture may be used. Also, the thickness of the oxide layer can be controlled by controlling the concentration, pH, mixing time, etc. of the solution containing the nonmetallic element.

The acicular powder obtained by heat reduction by the above method can be mixed with the resin to coat the acicular powder with the resin. There is no particular limitation on the method of coating with the resin. For example, the resin can be coated by adding a solution containing 20 to 60% by volume of resin to 100% by volume of acicular powder, mixing the mixture, and drying.

The composite magnetic material according to this embodiment can be obtained by mixing a plurality of types of acicular powders having different average aspect ratios at a predetermined ratio. When two types of acicular powders having different aspect ratios are mixed, the aspect ratio of the first peak or the second peak in the frequency distribution of the aspect ratios finally yields the average aspect ratio of each acicular powder. generally easy to match.

There is no particular limitation on the method of manufacturing the magnetic core from the above composite magnetic material, and a normal method according to this embodiment can be used.

For example, a magnetic core made of a powder compact can be manufactured by filling the above composite magnetic material into a mold and pressing it.

There is no particular limitation on the use of the magnetic core according to this embodiment. For example, coil components, LC filters, antennas, and the like are included.

Next, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

First, acicular powder was produced. The acicular powder was produced by a known method of heat-reducing powder composed of α-FeOOH in H ₂ .

At this time, a powder composed of a plurality of acicular α-FeOOH having different average aspect ratios was prepared. An acicular powder was finally obtained from the acicular α-FeOOH powder. By controlling the minor axis length, major axis length and average aspect ratio of the needle-shaped α-FeOOH powder at this time, acicular powder having the minor axis length, major axis length and average aspect ratio described in each table got the powder

Furthermore, by controlling the Co content in the powder composed of α-FeOOH, the composition of the acicular powder was controlled to the composition shown in each table. In addition, the composition shown in each table is an atomic number ratio.

A resin was added to the acicular powder obtained by the above method. In addition, acicular powder 1 and acicular powder 2 shown in each table were mixed at the volume ratio shown in each table. Using a mixing roll, the mixture was kneaded at 95° C., continued kneading with slow cooling to 70° C., stopped kneading at 70° C. or less, and was rapidly cooled to room temperature to obtain a composite magnetic material. As the resin, JER806 (Mitsubishi Chemical), which is an epoxy resin, was used.

Next, the obtained composite magnetic material was put into a mold heated to 100° C. and molded under a molding pressure of 980 MPa. The obtained molded body was heat-cured at 180° C. and then cut out to obtain magnetic cores of Examples and Comparative Examples shown in each table. The shape of the magnetic core was a rectangular parallelepiped of 1 mm×1 mm×100 mm.

The relative magnetic permeability μr and the magnetic loss tan δ of the examples and comparative examples were measured at a frequency of 1.0 GHz and a frequency of 3.5 GHz. The relative magnetic permeability μr and the magnetic loss tan δ were measured by the perturbation method using a network analyzer (HP8753D manufactured by Agilent Technologies) and a cavity resonator (manufactured by Kanto Denshi Applied Development Co., Ltd.). Results are shown in each table. A magnetic loss tan δ of 0.005 or less was considered good at a frequency of 1.0 GHz. In the case of a frequency of 3.5 GHz, 0.015 or less was considered good.

Also, of the two types of acicular powder included in each example, each table shows how much the relative magnetic permeability μr changed based on a comparative example using only acicular powder with a small average aspect ratio. did. The amount of change in relative magnetic permeability μr at a frequency of 1.0 GHz is defined as Δμ1, and the amount of change in relative magnetic permeability μr at a frequency of 3.5 GHz is defined as Δμ2.

Furthermore, the aspect ratio of 700 primary particles of acicular powder contained in the obtained magnetic core was measured, and a histogram was created. Then, the presence or absence of the second peak, whether or not the average minor axis length was 100 nm or less, and whether or not the aspect ratio of the first peak and the aspect ratio of the second peak were each 3.0 or more and 10 or less were evaluated. Furthermore, the aspect ratio ratio was calculated. Results are shown in each table. In addition, the histogram of Example 8 is illustrated in FIG.

Tables 1 and 2 show the results of Example 1 in which acicular powder having an average aspect ratio of 3.0 and acicular powder having an average aspect ratio of 5.0 were mixed, in the case where the acicular powder consisted only of iron. rice field. The results of Comparative Example 1 using only acicular powder with an average aspect ratio of 3.0 and Comparative Example 2 using only acicular powder with an average aspect ratio of 5.0 are also shown.

From Tables 1 and 2, the frequency distribution of the aspect ratio is a predetermined frequency distribution, and the average short axis length is also within a predetermined range. Compared with Example 1 and Comparative Example 2, the relative magnetic permeability μr was improved.

In Tables 3 and 4, when the acicular powder is an alloy of iron and cobalt, acicular powder with an average aspect ratio of 3.0 is added to acicular powder with an average aspect ratio of 4.1 to 9.9. The results of mixed Examples 2-12 are shown. Also, the results of Comparative Example 9, in which acicular powder having an average aspect ratio of 3.0 was mixed with acicular powder having an average aspect ratio of 12.2, were shown. Furthermore, the results of Comparative Examples 3 to 8 using only one type of acicular powder are shown.

From Tables 3 and 4, Examples 2 to 12, in which the aspect ratio frequency distribution is a predetermined frequency distribution and the average short axis length is also within a predetermined range, the aspect ratio frequency distribution has a second peak. Compared to Comparative Examples 3 to 8, which did not contain any sintered material, the relative magnetic permeability μr was improved.

Furthermore, even though it had a second peak, Comparative Example 9, in which the aspect ratio of the second peak was greater than 10.0, did not improve the relative magnetic permeability μr compared to Comparative Example 3.

In Tables 5 and 6, when the acicular powder is an alloy of iron and cobalt, acicular powder with an average aspect ratio of 4.1 is added to acicular powder with an average aspect ratio of 5.1 to 9.9. The results of mixed Examples 13-15 are shown. Also, the results of Comparative Example 11, in which needle-like powder having an average aspect ratio of 4.1 was mixed with needle-like powder having an average aspect ratio of 12.2, were shown. Furthermore, the results of Comparative Examples 4 to 8 using only one type of acicular powder are shown.

From Tables 5 and 6, Examples 13 to 15, in which the aspect ratio frequency distribution is a predetermined frequency distribution and the average minor axis length is also within a predetermined range, the aspect ratio frequency distribution has a second peak. Compared to Comparative Examples 4 to 8, which did not contain any sintered material, the relative magnetic permeability μr was improved.

Furthermore, even though it had a second peak, Comparative Example 11, in which the aspect ratio of the second peak was greater than 10.0, did not improve the relative magnetic permeability μr compared to Comparative Example 4.

In Tables 7 and 8, when the needle-like powder is an alloy of iron and cobalt, needle-like powder having an average aspect ratio of 7.3 is mixed with needle-like powder having an average aspect ratio of 9.9. The results of Example 16 are shown. Also, the results of Comparative Example 12, in which needle-like powder having an average aspect ratio of 7.3 was mixed with needle-like powder having an average aspect ratio of 12.2, were shown. Furthermore, the results of Comparative Examples 6 to 8 using only one type of acicular powder are shown.

From Tables 7 and 8, the aspect ratio frequency distribution is a predetermined frequency distribution, and the average short axis length is also within a predetermined range. Compared with Examples 6-8, the relative magnetic permeability μr was improved.

Furthermore, even though it had a second peak, Comparative Example 12, in which the aspect ratio of the second peak was greater than 10.0, did not improve the relative permeability μr compared to Comparative Example 6.

Tables 9 and 10 show Example 17 and Comparative Examples 13 and 14 using acicular powder having a longer average minor axis length than the acicular powders shown in Tables 1 to 8.

From Tables 9 and 10, the aspect ratio frequency distribution is a predetermined frequency distribution, and the average short axis length is also within a predetermined range. Compared with Examples 13 and 14, the relative magnetic permeability μr was improved.

Tables 11 and 12 show Comparative Examples 15 to 17 using acicular powders having a longer average minor axis length than the acicular powders shown in Tables 9 and 10.

From Tables 11 and 12, Comparative Examples 15 to 17, in which the average minor axis length was too long, resulted in excessively large magnetic loss tan δ regardless of the frequency distribution of aspect ratios.

1 Acicular powder 1a Ellipse (circumscribing acicular powder)

Claims (3)

A composite magnetic material containing acicular powder and resin,
The acicular powder is mainly composed of Fe or Fe and Co,
The primary particles of the acicular powder have an average minor axis length of 100 nm or less,
In the frequency distribution of the aspect ratios of the primary particles of the acicular powder, the aspect ratio of the first peak with the highest frequency and the aspect ratio of the second peak with the second highest frequency are in the range of 3.0 or more and 10 or less. can be,
(aspect ratio of first peak) / (aspect ratio of second peak) and (aspect ratio of second peak) / (aspect ratio of first peak), whichever is smaller is 0.30 or more and 0.80 or less A composite magnetic material characterized by: 2. The composite magnetic material according to claim 1, wherein the acicular powder has a Co content of 0 to 40 atom % (not including 0 atom %) relative to the main component. A magnetic core comprising the composite magnetic material according to claim 1 or 2.

Images