JPH11219812A - Oxide magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the hysteresis loss by a method wherein the Ni-Cu-Zn base ferrite main component composition contains a specific quantity of Fe2 O3 , NiO, CuO while residual part contains ZnO and sub-composition containing a specific quantity of MnO. SOLUTION: As for the main component composition, 48-49.5 mol.% in terms of Fe2 O3 , 17-23 mol.% in terms of NiO, 3-7 mol.% in terms of CuO with the residual part comprising ZnO while 4-9.5 wt.% of MnO as for the sub-component is contained in the oxide magnetic material. Besides, the mean crystalline particle diameter of a sintered body exceeds in this oxide magnetic material. Furthermore, the hysteresis loss can be remarkably extenuated by adding MnO to Ni-Cu-Zn base ferrite. The cause of this decrease can be supposed on the reduction of the anisotropical constant depending upon the hysteresis loss. On the other hand, the hysteresis loss can be decreased by increasing the mean crystalline particle diameter exceeding 8 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide magnetic material used for a transformer of a switching power supply or the like, and more particularly to a Ni-Cu-Zn ferrite having a spinel type crystal structure.

[0002]

2. Description of the Related Art In recent years, miniaturization of electronic devices such as portable devices has been rapidly progressing. And the power supply used for them is in the same flow. In the power supply, the transformer occupies a large proportion in terms of both volume and power loss, so it is urgently necessary to reduce its size and increase its efficiency. One solution is to increase the driving frequency, and a low-loss magnetic core material applicable to the driving frequency is desired.

The characteristics required of power transformer materials are as follows:
Low drive frequency, high saturation magnetic flux density, high Curie temperature, and high specific resistance.

[0004] If the loss of the transformer material is large, not only the efficiency as a power supply is poor, but also the risk of thermal runaway due to self-heating is generated. Therefore, ferrite materials for transformers currently used are required to have a low loss and a temperature at which the loss is minimized higher than the ambient temperature in order to minimize the temperature rise due to self-heating. .

As a material for a power transformer, an inexpensive Mn-Zn ferrite having a high saturation magnetic flux density (about 500 mT) is used. However, the Mn-Zn-based ferrite has a low specific resistance, and must be wound through a jig such as a bobbin in order to secure insulation. Therefore, there is a limit to miniaturization when using a Mn-Zn ferrite as a transformer material.

On the other hand, Ni—Zn-based ferrite has a high specific resistance and can be wound directly. In addition to the high specific resistance, the addition of Cu enables low-temperature sintering, so that the conductor and the magnetic material can be integrally sintered, and an unlimited size reduction can be realized. However, since the Ni—Zn ferrite has high loss, the efficiency is low and there is a risk of thermal runaway or the like.

[0007]

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

[0008]

In order to solve the above-mentioned problems, the present inventors have made various studies and found that Ni-C
In u-Zn ferrite, it is the main component composition, Fe ₂
48 to 49.5 mol% in terms of O ₃ , 17 to 23 mol% in terms of NiO, ₃ to 7 mol% in terms of CuO, and the balance being ZnO, and 4 to 9.5 wt.
% Of MnO and an average crystal grain size of 10 μm or more, it has been found that an oxide magnetic material having low loss and high specific resistance can be obtained.

That is, according to the present invention, as a main component composition, F
48～49.5Mol% in terms of e ₂ O _3, 17~23mol% in terms of NiO, 3-7 mol of% in terms of CuO
And the balance is ZnO, and 4 to 9.5 w
It is an oxide magnetic material containing t% MnO.

The present invention also relates to the above oxide magnetic material, wherein the sintered body has an average crystal grain size of 8 μm or more.

Regarding the loss of the Ni—Cu—Zn ferrite, the operating frequency is 50 kHz-150 mT, which is a normal operating environment.
The hysteresis loss accounts for 60 to 70%, and it is effective to reduce the hysteresis loss to reduce the loss.

Generally, it is known that the hysteresis loss is proportional to the anisotropy constant (K), and the anisotropy constant is composed of the magnetocrystalline anisotropy constant (K ₁ ) and the magnetostriction (λ). .
Further, by adding MnO to a Ni-Cu-Zn ferrite material and substituting a part of Fe ³⁺ with Mn ²⁺ ,
It is known that the magnetic moment at the B site decreases, the interaction energy between the spins decreases, and the magnetostriction decreases (Gerald F. Dionn, Russel G. West: J. Appl. Phys. 6).
1 (8), 15 April 1987).

It is also known that the hysteresis loss decreases as the crystal grain size increases, because the magnetic domain size is proportional to the crystal grain size.

According to the present invention, remarkable reduction of hysteresis loss can be achieved by adding MnO to Ni-Cu-Zn ferrite. Although the reason for this is not known in detail, it is believed that the substitution of Mn ²⁺ and Fe ³⁺ reduces the anisotropy constant (crystal magnetic anisotropy constant or magnetostriction) depending on the hysteresis loss. Inferred. Further, by setting the average crystal grain size to 8 μm or more, the hysteresis loss can be reduced.

[0015] The the Fe ₂ O ₃ was 48～49.5Mol%, when Fe ₂ O ₃ is less than 48 mol%, the power loss (P _CV) is because the increases, Fe ₂ O ₃ is 49. 5m
If the amount is more than ol%, the specific resistance decreases. Ni
The reason why O is set to 17 to 23 mol% is that NiO is 17 mol%.
When the content is less than l%, the saturation magnetic flux density (Bs) is because the drops, when NiO is more than 23 mol%, because the P _CV increases. Is to that with 3-7 mol of% of CuO, the CuO is less than 3 mol%, is because the sintered density is low, the CuO is more than 7 mol%, because the P _CV increases. The was a 4～9.5Wt% of MnO, when MnO is less than 4 wt%, is for the reduction of P _CV by MnO added is not performed, MnO 9.
If the content is more than 5 wt%, the sintered body density is low. Incidentally, MnO is the in the range of 5~8.5wt%, lower P _CV value is obtained.

Further, the average of the grain diameter is more than 8μm, the average crystalline grain diameter is 8μm smaller, because the P _CV increases by hysteresis loss increases. When the average crystal grain size is 10 μm or more, a lower _PCV value can be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS After weighing, mixing and calcining predetermined raw materials, MnO is added and pulverized. Then, a binder is added and granulated. Further, the oxide magnetic material of the present invention is obtained by molding and firing.

[0018]

(Example 1) The main component composition is Fe ₂ O ₃ : 47.
5 to 50 mol%, NiO: 14 to 26 mol%, Cu
O: 1 to 9 mol%, the raw materials are weighed so that the balance is ZnO, mixed using a ball mill, and mixed in an air atmosphere.
After calcining at 0 ° C. for 2 hours and adding 7 wt% of MnO as an auxiliary component, the mixture was finely pulverized by a ball mill. After finely pulverizing, add a binder and granulate with a spray drier.
It was molded into a toroidal shape of 30 × φ25 × 5 mm and sintered at 1100 ° C. in the air atmosphere. Further, a sample to which MnO was not added was prepared by the same method as a conventional material. Wind the obtained core, 50kHz-150mT
The core loss was measured at -80 ° C. In addition, Bs and specific resistance at room temperature were measured. Table 1 shows the composition and magnetic properties of the obtained sample.

[0019]

[Table 1]

As shown in Table 1, Fe ₂ O ₃ : 48 to 49.5 mol
1%, NiO: 17 to 23 mol%, CuO: 3 to 7 m
It can be seen that the magnetic properties superior to those of the conventional material are obtained with the main component composition of ol%.

Example 2 The main component composition is Fe ₂ O ₃ : 49.
mol%, NiO: 20 mol%, CuO: 4 mol
%, And the balance was ZnO, the raw materials were weighed, mixed using a ball mill, and calcined at 850 ° C. for 2 hours in an air atmosphere.
Fine grinding was performed with a ball mill. After fine pulverization, a binder was added, and the mixture was granulated with a spray drier.
It was formed into a 5 × 5 mm toroidal shape and sintered at 1100 ° C. in an air atmosphere. Wind the obtained core, 50
The core loss was measured under the conditions of kHz-150 mT-80 ° C. The result is shown in FIG.

From FIG. 1, it can be seen that the core loss is smaller than that of the conventional material (0 wt%) in the sample containing 4 to 9.5 wt% of MnO.

Example 3 The main component composition is Fe ₂ O ₃ : 49
mol%, NiO: 20 mol%, CuO: 4 mol
%, The balance being ZnO, weighing the raw materials using a ball mill, calcining at 850 ° C. for 2 hours in the air atmosphere, adding 7 wt% of MnO as an auxiliary component, and then pulverizing with a ball mill. Was. After fine pulverization, a binder was added and granulated with a spray drier.
5mm toroidal shape
Sintered at 00 to 1300 ° C. Further, as a conventional material, a sample having the same main component composition without adding MnO was sintered at 1100 ° C. in the air atmosphere by the same method. Wind the obtained core, 50kHz-150mT-80 ℃
The core loss was measured under the following conditions. Table 2 shows the average crystal grain size and magnetic properties of the obtained sample.

[0024]

From Table 2, it can be seen that the average crystal grain size is 8 μm or more, and the magnetic properties are superior to those of the conventional material.

[0026]

As described above, according to the present invention, a low-loss oxide magnetic material can be provided.

[Brief description of the drawings]

FIG. 1. Addition amount of MnO and 50 kHz-1500G-8
Diagram showing the relationship between the P _CV at 0 ° C..

Claims (2)

[Claims] 1. The composition of the main component is 4 in terms of Fe ₂ O _3.
8-49.5mol%, 17-23mo in NiO conversion
1%, 3 to 7 mol% in terms of CuO, and the balance being ZnO
An oxide magnetic material comprising 4 to 9.5 wt% MnO as a subcomponent. 2. The oxide magnetic material according to claim 1, wherein the average crystal grain size of the sintered body is 8 μm or more.