JPH11251132A - Low-loss oxide magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power loss and realize increase in the specific resistance, by substituting CaO for a specified mol.% of ZnO, which is a principal component of Ni-Zn ferrite. SOLUTION: Fe2 O3 , NiO, ZnO, CuO and Ca(OH) are measured to obtain a composition including Fe2 O3 at 49.0 mol.%, NiO at 11.0-16.0 mol.%, ZnO at 2 4.0-30.0 mol.%, CuO at 5.0 mol.% and CaO at 0-5.0 mol.%, and are mixed for 20 minutes in a wet method, dried, and pulverized. Next, the components are pre-fired in the atmosphere at 800 deg.C, dried, pulverized, and pressed. After that, the components are fired for 120 minutes at 1200 deg.C. As the power loss Pcv (50 kHz, 1500 G, 80 deg.C) and the saturation magnetic flux density Bs of the sintered body thus obtained are measured, it is found that Pcv is lowered with a CaO substitution quantity within a range of 0-5.0 mol.% (not including 0). The quantity of substitution of CaO for ZnO is set to more than 0 mol.% (not including 0) because even a very small substitution quantity increases the spacing between magnetic ions and thus has an effect of reducing the magnetic anisotropy. Thus, a power source can be miniaturized by having a low loss and a high specific resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low-loss oxide magnetic material used for a power transformer or a ferrite core for a choke coil.

[0002]

2. Description of the Related Art As a material used for a power transformer, Mn-Zn ferrite having a relatively high saturation magnetic flux density and a small power loss is mainly used. However, Mn
-Zn ferrite has a DC specific resistance of 10 to 10 ³ Ωcm
And low. Therefore, in order to eliminate defects such as short circuits, these magnetic cores are usually wound through bobbins, which is an obstacle to miniaturization, weight reduction and cost reduction.

On the other hand, Ni—Zn ferrite is generally
The DC specific resistance is as high as 10 ⁶ to 10 ¹⁰ Ωcm, and a bobbin is not required for winding, but the power loss is significantly higher than that of Mn-Zn ferrite.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an oxide magnetic material having small power loss.

[0005]

According to the present invention, there is provided a low-loss oxide magnetic material comprising ZnO, which is a main component of Ni--Zn ferrite.
Is characterized by substituting 0 to 5 mol% (not including 0) of Ca with CaO.

That is, according to the present invention, as a main component, 48 to 50 mol% of Fe ₂ O ₃ , 20 to 35 mol% of ZnO,
3 to 10 mol% of uO and 0 to 5 mol% of CaO (0
), And a low-loss oxide magnetic material consisting of the balance NiO.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Magnetic loss of ferrite consists of hysteresis loss, eddy current loss and residual loss. Ni
-Zn ferrite, generally, DC specific resistance of 10 ⁶ to 1
It is as high as 0 ¹⁰ Ωcm, and the eddy current loss is negligibly small. Hysteresis loss is loss caused by magnetic anisotropy. Among the magnetic anisotropies, the crystalline magnetic anisotropy is considered to be mainly caused by exchange interaction between magnetic ions via oxygen ions.

0-5 of Zn ^{2+ in} Ni—Zn ferrite
By replacing mol% (not including 0) with Ca ²⁺ having an ionic radius larger than that of Zn ²⁺ , the distance between magnetic ions is increased, the exchange interaction is weakened, and the crystal magnetic anisotropy is reduced. It is considered that the hysteresis loss can be reduced.

The reason why the ions to be replaced are nonmagnetic Zn ²⁺ is that the number of nonmagnetic ions does not change due to the replacement, and therefore, the saturation magnetic flux density (Bs) and the Curie temperature (Tc)
This is because there is little decrease.

The reason why the content of Fe ₂ O ₃ is 48 to 50 mol%, the content of ZnO is 20 to 35 mol%, and the content of CuO is ₃ to 10 mol% is that when the content of Fe ₂ O ₃ exceeds 50 mol%, the specific resistance decreases and ZnO becomes Over 35 mol% or Fe
₂ O ₃ is less than 48 mol% or CuO is 10 mol
%, Bs decreases.

On the other hand, if CuO is less than 3 mol%, the sintering temperature must be increased, and the specific resistance decreases. Further, if ZnO is less than 20 mol%, Pcv becomes large.

Further, the amount of ZnO to be replaced with CaO is 0 to
5 mol% (not including 0) is the substitution amount of 5 mo
If the content is more than 1%, Ca ²⁺ that cannot be dissolved in the spinel precipitates as a phase having a structure other than the spinel, and the power loss (Pcv), Bs, and Tc are significantly deteriorated. Further, the amount of ZnO to be replaced by CaO is 0 m.
% or more (not including 0), it is not general to add a small amount of CaO to the Ni—Zn ferrite, but even if the substitution amount is very small, the distance between the magnetic ions is increased and the magnetic difference is increased. This is because there is an effect of reducing anisotropy.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Fe ₂ O ₃ , NiO, ZnO, CuO and C
a (OH) ₂ is composed of 49.0 mol% of Fe ₂ O ₃ , 11.0 to 16.0 mol% of NiO, and 24.0 to 30.0 mol of ZnO.
mol%, CuO is 5.0 mol%, and CaO is 0 to 5.0.
The mixture was weighed so as to have a composition of mol%, mixed for 20 minutes in a wet system, dried, granulated, and calcined in the air at 800 ° C.
The obtained powder was wet-ground for 120 minutes, dried, granulated, and pressed. Then, in air at 1200 ° C. for 120
Bake for a minute. The sintered body thus obtained (dimensions: 15 m
Pcv (50 kHz-1) of mφ-10 mmφ-5 mm)
500G-80 ° C), Bs and Tc were measured. The lattice constant was calculated from the X-ray diffraction peak of the powder obtained by crushing the sintered body. The specific resistance of the sintered body was 10 ⁸
Ωcm. Table 1 shows the measurement results for each sample.

[0014]

In Table 1, as compared with the sample numbers, the sample numbers and the lattice constants of the sample numbers are increased by replacing ZnO with CaO, and Pcv decreases as the substitution amount increases. This can be achieved by substituting the Zn ²⁺ of Ni-Zn ferrite in ionic radius larger Ca ²⁺ than Zn ^2+, the exchange interaction is weakened distance between magnetic ions increases, the crystal magnetic anisotropy This is considered to be due to a decrease in the hysteresis loss due to a decrease in the hysteresis loss. Also, the sample number, Tc and Bs
The decline is very slight. The sample number has a larger substitution amount than the sample number, but the lattice constant does not change, Pcv increases, and Bs and Tc decrease. This is considered to be because Ca ²⁺ which cannot be dissolved in the spinel is precipitated as a phase having a structure other than the spinel. Ni
In the case of the sample number in which O was reduced and CaO was added, and in the case of the sample number in which ZnO was reduced and CaO was added, the number of nonmagnetic ions was increased.
The decrease of c is remarkable.

FIG. 1 shows P in Sample Nos.
The relationship between cv and the amount of CaO substitution was shown. According to FIG.
It can be seen that Pcv is reduced when the O substitution amount is in the range of 0 to 5.0 mol% (not including 0).

FIG. 2 shows the temperature characteristics of Pcv in the sample numbers in Table 1. From FIG. 2, it can be seen that the loss of the sample number (product of the present invention) is reduced in all ranges from room temperature to 120 ° C. as compared with the sample number (comparative product).

In addition, other than the compositions shown in Table 1, 0 to 5 mol% of ZnO, which is the main component, is within the scope of the present invention.
The same effect can be obtained by replacing (not including 0) with CaO.

[0019]

As described above, according to the present invention,
0-5 m of ZnO, the main component of Ni-Zn ferrite
By replacing ol% (not including 0) with CaO, an oxide magnetic material with low power loss can be provided.
Since the oxide magnetic material of the present invention has not only low loss but also high specific resistance, a bobbin is not required, and the effects of reducing the size and cost of a power supply can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between Pcv and CaO substitution amount.

FIG. 2 is a diagram showing sample numbers shown in Table 1 and temperature characteristics of Pcv from room temperature to 120 ° C. in the sample numbers.

[Explanation of symbols]

 1 inventive product (sample number) 2 comparative product (sample number)

Claims (1)

[Claims] 2. A method according to claim 1, wherein the main component is Fe ₂ O ₃ in an amount of 48 to 50 mo.
1%, ZnO 20-35 mol%, CuO 3-10
A low-loss oxide magnetic material comprising: mol%, 0 to 5 mol% of CaO (not including 0), and the balance being NiO.