JP2000306719A - Low-loss oxide magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for a bobbin because of not only low loss but also high specific resistance and to make a power source small-sized, lightweight, and low-cost. SOLUTION: This material consists principally of 48 to 50 mol% (where <50 mol% is excluded) Fe2O3, 20 to 32 mol% ZnO, 3 to 7 mol% CuO, and the balance for NiO. 0 to 5 mol% (where 0 is excluded) of ZnO is substituted for MgO and the mean crystal particle size of a sinter is 5 μm or larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-loss oxide magnetism used for a magnetic core such as a transformer for a switching power supply and a choke coil.

[0002]

2. Description of the Related Art Conventionally, Mn-Zn ferrites having relatively high saturation magnetic flux density and low power loss have been mainly used as magnetic core materials for transformers for switching power supplies and choke coils.

[0003] However, miniaturization of electronic equipment,
As the weight and performance have been reduced, the requirements for components used in such devices have become even more severe, and Mn-Zn based ferrites have become unable to meet these requirements. That is, since the DC specific resistance of the Mn-Zn-based ferrite is as low as 10 ¹ to 10 ³ Ωcm, it is usually necessary to wind these magnetic cores through a bobbin in order to eliminate defects such as short circuits. This is an obstacle to miniaturization, weight reduction, and cost reduction.

Therefore, in general, the DC specific resistance is 10 ⁶ to 1
Practical application of Ni—Zn based ferrite, which is as high as 0 ¹⁰ Ωcm and does not require a bobbin when performing winding, has been studied.

[0005]

However, the magnetic core of the Ni-Zn ferrite has a drawback that the power loss due to the hysteresis loss is large, and the miniaturization, weight reduction, high performance and cost reduction are required. There was a problem that it was difficult.

Accordingly, an object of the present invention is to provide a low-loss oxide magnetic material that solves the above-mentioned problems.

[0007]

The present invention SUMMARY OF] is, 48～50Mol% principal component composition (not inclusive of 50 mol%) of _Fe 2 _O 3, _20~32mol% of ZnO, 3～7Mo
1% CuO, balance NiO, ZnO 0-5m
It is a low-loss oxide magnetic material made of a sintered body in which ol% (excluding 0) is substituted with MgO.

Further, the present invention is a low-loss oxide magnetic material having an average crystal grain size of the sintered body of 5 μm or more.

[0009] Ferrite loss is roughly classified into hysteresis.
It consists of cis loss, eddy current loss, and residual loss. Ni
-Zn ferrite generally has a DC specific resistance of 10⁶~
10 ¹⁰High Ωcm, negligible eddy current loss
However, the hysteresis loss is large. Hysteresis loss
Is a loss caused by magnetic anisotropy. Magnetic anisotropy
Of the crystalline magnetic anisotropy is mainly through oxygen ions
Probably caused by exchange interaction between magnetic ions
You.

Therefore, Zn in the Ni—Zn ferrite
0 ^{+ 5} mol% (but not including 0) of ²⁺
Hysteresis loss can be reduced by substituting Mg ²⁺ having a smaller ionic radius than that. Non-magnetic Zn ²⁺ was used as the ion to be replaced because Zn ²⁺ ion and Mg ²⁺
Substitution of ²⁺ ions is substitution between non-magnetic ions,
Since the number of non-magnetic ions does not change, the saturation magnetic flux density (B
s) and the Curie temperature (Tc) are small.

The amount of replacing ZnO with MgO is 5 mol%
If the substitution amount is more than 5 mol%, Mg ²⁺ which cannot be dissolved in the spinel precipitates as a phase having a structure other than the spinel, and the loss (Pcv), the saturation magnetic flux density (Bs), And the Curie temperature (Tc) is significantly deteriorated.

The amount of ZnO to be replaced by MgO is 0 m.
ol% or more (however, 0 is not included) is because Ni-Z
This is because the addition of a small amount of MgO to the n-type ferrite is not general and has an effect of increasing the distance between magnetic ions and reducing magnetic anisotropy.

When the main component composition is 48 to 50 mol% (however,
50 mol% is not included) Fe₂O ₃, 20-32mo
1% ZnO, 3-7 mol% CuO, balance NiO
The reason is that Fe₂O₃Is 48 mol% or less,
The magnetic loss at room temperature increases significantly, to over 50 mol%
Then, Fe²⁺Causes the resistivity to be extremely low
It is because it becomes.

If ZnO is less than 20 mol%, the loss at room temperature becomes large, and if it exceeds 32 mol%, Bs, Tc
Will be reduced. When CuO exceeds 7 mol%, abnormal grains are generated, causing an increase in loss. When CuO is less than 3 mol%, the average crystal grain size becomes less than 5 μm, and the loss increases.

The reason why the average crystal grain size is set to 5 μm or more is as follows.
This is because the loss is increased below μm.

[0016]

Embodiments of the present invention will be described below.

(First Embodiment) Fe ₂ O ₃ , Ni
O, ZnO, MgO, and CuO are weighed so as to have the compositions shown in Tables 1 to 8, mixed in a wet system for 20 minutes, dried, granulated, and calcined in the air at 800 ° C. to obtain The powder thus obtained was pulverized by a wet method for 120 minutes, dried, granulated, and pressed.
Then, it baked at 1200 degreeC for 120 minutes in air | atmosphere.

[0018]

[Table 1]

The sintered body thus obtained (dimensions: 15 mm
Pcv, Ph, Bs, and T of φ-10 mmφ-5 mm, specific resistance: 10 ⁸ Ωcm, and average crystal grain size: 14 μm)
c was measured.

Table 1 shows the results of each measurement. Invention 2,
Pcv and Ph are lower in Comparative Examples 3 and 4 than in Comparative Product 1, and Pcv and Ph decrease as the amount of added MgO increases. This is because Zn in Ni—Zn ferrite
^It is considered that the substitution of ²⁺ with Mg ²⁺ having an ionic radius smaller than that of Zn ²⁺ reduced the crystal magnetic anisotropy and reduced the hysteresis loss.

The invention products 2, 3, and 4 also have a very small decrease in Tc and Bs as compared with the comparison product 1. The comparative product 5 has a larger substitution amount than the inventive product 4, but has an increased Pcv and decreased Bs and Tc. This is considered to be because Mg ²⁺ which cannot be dissolved in the spinel is precipitated as a phase having a structure other than the spinel.

Comparative products 6, 7, and 8 are magnetic ions of N
Due to the substitution with ^{Mg 2 +} a i ²⁺ is a non-magnetic ions, as compared with the conventional product 1, reduction of Bs and Tc is remarkable.

FIG. 1 shows a conventional product 1 and an invention product 4 shown in Table 1.
3 shows the temperature characteristics of Pcv. Inventive product 4 has a reduced loss in the range from room temperature to 120 ° C. as compared to comparative product 1.

(Second Embodiment) Fe ₂ O ₃ , Ni
O, ZnO, MgO, and CuO are weighed so as to have the compositions shown in Tables 9 to 20, mixed by a wet method for 20 minutes, and dried.
After granulation, the powder was calcined in the air at 800 ° C., and the obtained powder was wet-pulverized for 120 minutes, dried, granulated, and pressed.

Then, at 1200.degree.
Bake for 0 minutes. The sintered body thus obtained (dimensions: 15
mmφ-10mmφ-5mm) Pcv, Bs, Tc,
The average crystal grain size and specific resistance were measured.

Table 2 shows the results of each measurement.

[0027]

[Table 2]

Fe ₂ O ₃ is 48 to 50 mol% (provided that
Inventive products 10 and 11 (not including 50 mol%) have higher specific resistance and less loss compared to comparative products 9 and 12. Inventions 14 to 16 with ZnO of 20 to 32 mol%
Has higher Bs and Tc and lower loss compared to the comparative products 13 and 17. The invention product 19 having CuO of 3 to 7 mol% has a smaller loss as compared with the comparison products 18 and 20.

(Third Embodiment)

49.0 mol% of Fe ₂ O ₃ , 16 mo
1% NiO, 25 mol% ZnO, 5 mol% M
gO, weighed to 5 mol% CuO, mixed for 20 minutes in a wet system, dried and granulated, calcined in the air at 800 ° C, pulverized the obtained powder for 120 minutes in a wet system, dried and granulated.
It was granulated and pressed.

After that, the invention product 22 becomes 1 in the atmosphere.
It was baked at 200 ° C. for 120 minutes. In addition, the comparative product 21
It baked at 1000 degreeC for 120 minutes in air | atmosphere. The sintered body thus obtained (dimensions: 15 mmφ-10 mmφ-5 m
m) Pcv, Bs, Tc, average crystal grain size, and specific resistance were measured.

Table 3 shows each measurement result.

[0033]

[Table 3]

Invention 22 having an average crystal grain size of 10 μm or more
Has a smaller loss as compared with the comparative product 21.

[0035]

As described above, according to the present invention, according to the present invention, _Fe 2 _O 3 of 48～50Mol% main component composition (not inclusive of 50mol%), 20~32mol% of ZnO,
3 to 7 mol% CuO, balance NiO, ZnO
Characterized by substituting 0 to 5 mol% (but not including 0) of MgO with MgO, and having an average crystal grain size of 5
When the thickness is at least μm, a low-loss oxide magnetic material can be obtained. Since the product 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, weight, and cost of the power supply can be expected.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows room temperature of comparative product 1 and inventive product 4 shown in Table 1
The figure which shows the temperature characteristic of 20 degreeC Pcv (50kHz-1500G).

Claims (2)

[Claims] 1. Fe ₂ O _{3 having} a main component composition of 48 to 50 mol% (but not including 50 mol%), 20 to 32
mol% ZnO, 3-7 mol% CuO, balance Ni
A low-loss oxide magnetic material comprising a sintered body comprising O and substituting 0 to 5 mol% (excluding 0) of ZnO with MgO. 2. The low-loss oxide magnetic material according to claim 1, wherein the average crystal grain size of the sintered body is 5 μm or more.