JP3491035B2 - Ferrite powder for giant magnetoresistive material, sintered ferrite and bulk magnetoresistive element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bulk magnetoresistive element utilizing a giant magnetoresistive effect, particularly a ferrite powder for a giant magnetoresistive effect material which can be used for a magnetic sensor (position, rotation, gear sensor, etc.) and a magnetic head. , A ferrite sintered body for same use, and a bulk magnetoresistive element.

[0002]

2. Description of the Related Art Since the giant magnetoresistive effect (GMR) of a metallic artificial lattice such as Fe / Cr system has been conventionally developed, this GMR is not limited to the metallic artificial lattice, but also to the metal-metallic particle type alloy and the metal-metallic particle lattice. Non-metallic particle type alloys and the like have been studied, and since the magnetic resistance ratio (MR ratio) is large, magnetic heads and magnetic sensors have been actively developed. At present, the giant magnetoresistive effect is obtained by the nano-sized metal magnetic material in both the artificial lattice and the particle type alloy system.

As described above, in any of these cases, it is necessary to control the thickness of the magnetic material to the nano size.
It was necessary to use a thin film forming apparatus such as sputtering or vapor deposition, and thereby to manufacture a magnetoresistive material. But,
When the magnetoresistive material is produced in the vapor phase as described above, it is not easy to separate the magnetic substance from the non-magnetic substance, and it is sensitive to production factors such as gas pressure, input power, target material, and substrate material. . Therefore, in the production of the magnetoresistive material, there is a problem that it is difficult to reproduce the optimum conditions. In addition, it is necessary to process into a specific magnetoresistive element shape, but it is necessary to process using advanced technology such as microfabrication technology, which has the drawback of complicating the work and increasing the cost. There is. In addition, since these materials are mainly composed of a metal magnetic material, they have poor environment resistance such as heat resistance and corrosion resistance, and there are many problems for practical use. Further, the particle-type alloy system has a drawback of low external magnetic field sensitivity because it requires suppression of spin thermal disturbance of the magnetic material.

In order to solve such a problem, the present inventors previously prepared a magnetoresistive material in which fine crystal grains containing fine Fe as a main component were dispersed in an iron oxide matrix containing magnetite as a main component. Proposed (Japanese Patent Application No. 11-23641
No. 8). This is because although the MR ratio can be improved by making the giant magnetoresistive effect (GMR) appear, and it is excellent as a bulk material, the MR ratio is still inferior to that of the conventional particle type thin film. We have not reached the target level. In this case, the metal (Fe)
Because of the presence of the components, it has poor corrosion resistance and is easily rusted.
It leaves some problems. The present invention improves on this.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to develop a bulk giant magnetoresistive material mainly composed of an oxide magnetic material and excellent in environmental resistance, not a thin film manufacturing technique. Another object is to develop a bulk magnetoresistive effect material having characteristics comparable to or exceeding the MR ratio shown by the conventional particle type thin film by combining another insulator with the M.Fe ₂ O ₄ oxide magnetic material. To do. Furthermore, in order to improve the external magnetic field sensitivity, it is an object to develop a device having a composite shape element made of an oxide bulk magnetoresistive material and a bulk soft magnetic material and capable of precision processing.

[0006]

According to the present invention, 1) M.Fe ₂ O ₄ (M: M) having an average particle size of 10 nm to 700 nm.
n, Fe, Co, Ni, Cu, Zn, Mg) The Fe ₂ O ₃ insulating layer is formed on the surface of the ferrite powder by heat-treating the ferrite powder in an oxygen-containing atmosphere or in the air. Ferrite powder for magnetoresistive effect material, 2) Heat treatment at 100 to 300 ° C, Ferrite powder for giant magnetoresistive effect material according to the above 2, 3) M having an average particle size of 10 nm to 700 nm
_{· Fe 2 O 4 (M:} Mn, Fe, Co, Ni, Cu, Z
n, Mg) A ferrite powder for a giant magnetoresistive material, characterized in that an insulating layer is formed on the surface of the ferrite powder by an insulating organic material. 4) The electrical resistivity is 10 ³ μΩcm or more. The ferrite powder for giant magnetoresistive effect material according to any one of the above 1) to 3), 5) M · Fe ₂ O having an average particle size of 10 nm to 700 nm with an insulating layer formed on the surface.
₄ (M: Mn, Fe, Co, Ni, Cu, Zn, Mg)
Ferrite powder in a temperature range of 200 to 1000 ° C,
A ferrite sintered body for a giant magnetoresistive effect material, characterized by being sintered under a sintering pressure of 50 to 300 MPa;
6) The ferrite sintered body for giant magnetoresistive effect material according to 5), wherein the surface insulating layer is a heat-treated Fe ₂ O ₃ insulating layer or an insulating layer made of an insulating organic material.
7) The average particle size of the insulating layer formed on the surface is 10 nm to 70
0 nm of M · Fe ₂ O ₄ (M: Mn, Fe, Co,
Ni, Cu, Zn, Mg) Sintering with ferrite powder
The body in a soft magnetic material, or the sintered body and the soft magnetic material
Bulk magnetoresistive element characterized by being combined by laminating and 8) a soft magnetic material having a coercive force of 10 Oe.
The bulk magnetoresistive element according to 7) above, which is a bulk soft magnetic material having a magnetic permeability of 10 ³ or more, and 9) the surface insulating layer is a Fe ₂ O ₃ insulating layer or insulating property by heat treatment. 9. A bulk magnetoresistive element as described in 7 or 8 above, which is an insulating layer made of an organic material.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION M.Fe ₂ O ₄ used in the present invention
(M: Mn, Fe, Co, Ni, Cu, Zn, Mg) Ferrite has a Curie temperature (T _c ) of 300 to 600 °.
It is C, and has excellent environment resistance (heat resistance, corrosion resistance) as compared with the metal magnetic material. The present invention has a powder size of, for example, 1
M · Fe ₂ O ₄ (M: Mn, Fe, C
o, Ni, Cu, Zn, Mg) ferrite powder is milled by a vibration mill or a rotary mill for 10 to 300 hours to obtain fine M.Fe ₂ O ₄ (M: Mn, Fe, C).
o, Ni, Cu, Zn, Mg) ferrite powder.
At this time, the milling time and the atmosphere (O ₂ ,
While adjusting the Ar gas, M · Fe ₂ O ₄ (M: M
(n, Fe, Co, Ni, Cu, Zn, Mg) Ferrite powder is adjusted to a powder size of 10 nm to 700 nm.
The particle size of this ferrite powder is important,
The improvement of the giant magnetoresistive effect is already recognized at m to 700 nm.

Next, the thus obtained 10 nm to 70 nm
0 nm M · Fe_TwoO_Four(M: Mn, Fe, Co, N
i, Cu, Zn, Mg) ferrite powder in an oxygen-containing atmosphere
5 minutes to 1 at 100 to 300 ° C in the atmosphere or atmosphere
Heat treatment for 0 hours. This gives the ferrite powder table
Fe on the surface_TwoO_ThreeAn insulating layer is formed. The above 100 °
Fe less than C, even if heat treated for more than 10 hours_Two
O _ThreeIs difficult to form, and under the condition of over 300 ° C
Is Fe even after heat treatment for 5 minutes_ThreeO_FourIs all Fe_TwoO_ThreeAcid
On the surface of the ferrite powder._TwoO_ThreeInsulation
In order to form the layer stably, the above range of conditions should be satisfied.
Is desirable. Instead of this heat treatment, M ・ Fe_TwoO_Four(M:
Mn, Fe, Co, Ni, Cu, Zn, Mg) Ferrai
Powder in a solution of ethyl alcohol, acetone, etc.
Mill with powder of stearic acid, or
By using the chemical reaction in these solutions, the chemical reaction on the surface
It is also possible to form an insulating layer. In addition, alcohol
Since acetone and acetone are highly volatile substances, these are usually
Not considered to form an edge layer. However, the above
It is the viscosity of these solvents that is modified during the ring process.
It can be confirmed from the increase and the odor, and as a result, it is extremely thin.
An edge coating layer is formed. The reason for this is not always clear
Although it is not certain, this insulating layer is a new surface of the object to be ground (powder)
Normally caused by catalysis and impact energy
That a dilute polymer compound that could not be obtained was synthesized
It is speculated that this is due to M ・ Fe according to the above_TwoO
_Four(M: Mn, Fe, Co, Ni, Cu, Zn, Mg)
By adjusting the size of the ferrite powder and forming the insulating layer
10^ThreeAn electrical resistivity of μΩcm or more can be obtained.

Next, M.Fe having an insulating layer formed on its surface_Two
O_Four(M: Mn, Fe, Co, Ni, Cu, Zn, M
g) 200 to 100 of the ferrite powder using the sintering method.
Sintering pressure of 50 to 300 MPa is applied in the temperature range of 0 ° C.
By adjusting M ・ Fe _TwoO_Four(M: Mn, F
e, Co, Ni, Cu, Zn, Mg) Theory of ferrite
It is possible to obtain a good sintered body close to the density. This place
In case of less than 200 ° C. and less than 50 MPa,
If a sintered body cannot be obtained and the temperature exceeds 1000 ° C,
Has a crystal grain size of 1000 nm or more.
Surround M · Fe including the insulating layer_TwoO_Four(M: M
n, Fe, Co, Ni, Cu, Zn, Mg) ferrite
The sintered body is made by controlling the composition or thickness of the insulating layer.
MR of 5 to 20% with an external magnetic field of 10 kOe or more
A giant magnetoresistive (GMR) material exhibiting a ratio is obtained.

This giant magnetoresistive material is M.Fe ₂ O ₄ (M: Mn, Fe, Co, Ni, C) as described above.
u, Zn, Mg) A high resistance material having an electric resistivity of 10 ³ μΩcm or more including an insulating layer other than ferrite. This giant magnetoresistive material is M.Fe ₂ O ₄ (M: Mn, F
e, Co, Ni, Cu, Zn, Mg) This is a tunneling type magnetoresistive effect (TMR) because a change in magnetoresistance occurs when the magnetic spin tunnels through the insulating layer formed on the surface of the ferrite magnetic powder. You can confirm that.

Next, M.Fe ₂ O having the above characteristics
₄ (M: Mn, Fe, Co, Ni, Cu, Zn, Mg)
In order to increase the magnetoresistive sensitivity of the ferrite sintered body to an external magnetic field, M · Fe ₂ O ₄ (M: Mn, Fe, Co,
A bulk soft magnetic material having a coercive force of 10 Oe or less and a magnetic permeability of 10 ³ or more is attached to both sides of a Ni, Cu, Zn, Mg) ferrite sintered body to form a bulk magnetoresistive element. The bulk soft magnetic material / bulk magnetoresistive material / bulk soft magnetic magnetoresistive element thus manufactured is
Compared with a thin film magnetoresistive element formed by a fine processing technique, shape processing is easier, and precision processing capable of meeting industrial needs has a remarkable effect that can be achieved very easily. In addition, the bulk magnetoresistive element is made to have a shape of 10 to reduce the influence of the demagnetizing field due to the shape of the bulk soft magnetic material to the utmost.
The MR ratio for a weak magnetic field of 0 Oe or less is
Fe ₂ O ₄ (M: Mn, Fe, Co, Ni, Cu, Z
(n, Mg) It has an excellent feature that it can obtain a numerical value equivalent to the MR ratio of only the ferrite magnetoresistive effect material. The magnetoresistive element of bulk soft magnetic material / bulk magnetoresistive material / bulk soft magnetic material can also be formed by embedding a sintered body in a soft magnetic material or by forming a multilayer. As described above, the present invention includes all bulk magnetoresistive elements in which a sintered body using ferrite powder and a soft magnetic body are combined.

Since the magnetic field detection for the external magnetic field in the composite shape element made of the metal soft magnetic material and the oxide giant magnetoresistive effect material is performed by the voltage change of the composite shape element, the electrical resistivity of the oxide giant magnetoresistive effect material. The larger the size of the soft magnetic material, the easier it is to detect the output of the change in magnetic resistance. Therefore, the soft metal magnetic material (100
By electrical resistivity of .mu..OMEGA.cm below) is used and the oxide giant magnetoresistance effect material (10 ³ .mu..OMEGA.cm or more) give a 10-fold difference has the effect that the loss of output is small to read.

[0013]

EXAMPLES Next, the present invention will be explained based on examples.
It should be noted that the present embodiment is for facilitating the understanding of the present invention, and the present invention is not limited by these examples. (Example _{1) M · Fe 2 O 4} (M: Mn, Fe, Co,
The giant magnetoresistive effect in the oxide bulk mainly composed of (Ni, Cu, Zn, Mg) ferrite powder is a phenomenon caused by the spin of the magnetic substance tunneling at the interface. In order to improve the giant magnetoresistive effect of this material, it is considered necessary to increase the ratio of the tunnel area to the total area and to form an electrically stable insulating layer at the interface. Therefore, in the present invention, first, Fe ₃ O ₄ powders produced under the respective conditions are used, and the results of the influence of the powder size on the giant magnetoresistive effect and the influence of the insulating layer formed at the interface are shown in FIGS. 1 to 4. Show.

FIG. 1 shows a change curve of the magnetoresistive ratio (MR ratio) in the Fe ₃ O ₄ bulk obtained by sintering each Fe ₃ O ₄ powder using a sintering apparatus at 500 ° C. for 10 minutes. .
Fe ₃ O ₄ powder prepared before sintering was a raw material powder (average grain size was 1 μm) in order from the lowest MR ratio, a powder milled for 150 hours with a vibration mill, and further after milling 2
It is a powder that has been heat-treated in the atmosphere of 00 ° C. Compared with the sintered body produced only from the raw material powder, the MR ratio increases up to 2% when sintered using the powder milled for 150 hours. The average size of the raw material powder is 150 μm compared to 1 μm.
Since the average size of the milled powder decreases to 200 nm, it is considered that the cause of the increase in the MR ratio is that the ratio of the tunnel area of the sample increased due to the refinement of the Fe ₃ O ₄ powder by milling. . Furthermore, when the milled powder is sintered using the powder heat-treated in the air, a remarkable increase in the MR ratio, that is, the MR ratio increases up to 3.4%, is observed.

In order to investigate the cause of such characteristic improvement,
Milled powder sinter and both powders after heat treatment after milling
The components of the unsintered body were examined by X-ray diffraction. The result is
As shown in FIG. Milling sintered body is Fe_ThreeO_FourSingle layer crystal structure
Shows the structure. However, the heat-treated milling sintered body is Fe_Three
O_FourBesides Fe_TwoO_ThreeThe existence of Also, each
The electric resistivity of the sintered body is 5 × 10^ThreeΩcm and
5 x 10 ^FourMR ratio increased because it showed Ωcm
The cause is electrically stable Fe_TwoO_ThreeInsulating layer is Fe_ThreeO_Four
It is considered that this is because it was formed at the interface of the powder. Furthermore
Fig. 3 shows the IV characteristics of the heat-treated powder sintered body.
Show. Current density J (10^FourA
m^-2) Shows a non-linear behavior, the above Fe
_ThreeO_FourGiant magnetoresistive effect in bulk materials mainly composed of iron
The result is that the spin of the magnetic material tunnels through the insulating layer at the interface.
It turned out that it is caused by doing.

(Example 2) As a method for forming an insulating layer at the interface, not only heat treatment of powder but also formation of an insulating layer by a chemical reaction was investigated. FIG. 4 shows the MR ratio in the bulk obtained by sintering Fe ₃ O ₄ powder in an ethyl alcohol solution for milling at 500 ° C. for 10 minutes. As is clear from FIG. 4, it is higher than that of the bulk material in which the insulating layer of Fe ₂ O ₃ is formed at the interface by the heat treatment shown in FIG. It is considered that this is because a more uniform insulating layer was formed at the interface of the Fe ₃ O ₄ powder during the milling process. Therefore, the formation of an insulating layer by such a chemical reaction or an insulating organic material is also effective in improving the giant magnetoresistive effect.

(Embodiment 3) The oxide bulk magnetoresistive material mainly composed of Fe ₃ O ₄ has an MR ratio equal to or higher than that of a particle type thin film, but has low sensitivity to an external magnetic field. Therefore, there is a drawback that it is difficult to apply to actual products. Therefore, in the present invention, in order to enhance the sensitivity of the external magnetic field, a structure was proposed in which a soft magnetic material having a high magnetic permeability in a weak magnetic field is arranged on both sides of the oxide giant magnetoresistive material, and its magnetic field sensitivity was investigated. . That is, a rod-shaped structure in which an oxide giant magnetoresistive material is sandwiched between a soft magnetic material of an Fe—Ni alloy that strongly magnetizes in a weak magnetic field, for example, Fe ₁₉ Ni ₈₁ , is manufactured, and the MR ratio change in weak magnetism is investigated. It was The result is shown in FIG. In the same figure, for comparison, the results were compared with the results of only the oxide giant magnetoresistive effect material (Fe ₃ O ₄ bulk material). The magnetic field sensitivity at 100 Oe shows a change in MR ratio of 4.5% in the structure in which soft magnetic materials are arranged on both sides, which is 20 times higher than that of the Fe ₃ O ₄ bulk material containing only the oxide giant magnetoresistive effect material. As described above, the external magnetic field sensitivity is improved.

[0018]

According to the present invention, the average particle size to form an insulating layer on the surface is 10nm~700nm M · _Fe 2 O
₄ (M: Mn, Fe, Co, Ni, Cu, Zn, Mg)
By using ferrite powder, MR with characteristics comparable to or superior to the conventional thin film giant magnetoresistive material
It has a remarkable effect that a bulk giant magnetoresistive material having a good ratio and excellent environment resistance can be obtained. Furthermore, by producing a composite shaped element composed of an oxide bulk magnetoresistive effect material and a bulk soft magnetic material, the external magnetic field sensitivity is improved, and precision processing is possible, which is an excellent effect.

[Brief description of drawings]

FIG. 1 uses Fe ₃ O ₄ powders produced under the respective conditions,
It is a figure which shows the test result of the magnetic field dependence of MR ratio in the bulk sintered at 500 degreeC for 10 minutes.

FIG. 2 is a view showing an X-ray diffraction result of a sintered body of milling powder and a sintered body of powder subjected to heat treatment after milling.

FIG. 3 is a diagram showing current density-voltage (IV) characteristics of a sintered body of powder that has been heat-treated.

FIG. 4 is a diagram showing the magnetic field dependence of the MR ratio in a bulk obtained by milling Fe ₃ O ₄ powder in an ethyl alcohol solution and sintering the powder at 500 ° C. for 10 minutes.

FIG. 5: Fe ₁₉ Ni ₈₁ / Fe ₃ O ₄ / Fe ₁₉ Ni
₈₁ is a diagram showing the magnetic field dependence of the MR ratio in the bulk material and the _Fe 3 _{O 4} bulk materials.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Lee Kisaku 2-10-7-104 Taichiro, Taichiro-ku, Sendai-shi, Miyagi (56) Reference JP-A-11-289115 (JP, A) JP-A-2001- 60308 (JP, A) JP 10-92640 (JP, A) JP 7-82302 (JP, A) JP 5-315180 (JP, A) JP 61-159778 (JP, A) JP-A-11-274599 (JP, A) International publication 00/026683 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 43/08 G01R 33/09 G11B 5/39 H01F 1/34 H01F 10/20

Claims (9)

(57) [Claims] 1. M.Fe ₂ O ₄ (M: Mn, Fe, Co, Ni, Cu, having an average particle diameter of 10 nm to 700 nm)
A ferrite powder for a giant magnetoresistive effect material, characterized in that a Fe ₂ O ₃ insulating layer is formed on the surface of the ferrite powder by heat-treating the Zn, Mg) ferrite powder in an oxygen-containing atmosphere or in the air. 2. The ferrite powder for giant magnetoresistive effect material according to claim 1, which is heat-treated at 100 to 300 ° C. 3. M.Fe ₂ O ₄ (M: Mn, Fe, Co, Ni, Cu, having an average particle diameter of 10 nm to 700 nm)
Zn, Mg) ferrite powder by an insulating organic material,
A ferrite powder for giant magnetoresistive effect material, characterized in that an insulating layer is formed on the surface of the ferrite powder. 4. The ferrite powder for giant magnetoresistive effect material according to claim 1, which has an electric resistivity of 10 ³ μΩcm or more. 5. The average particle size of an insulating layer formed on the surface is 10
nm-700 nm of M · Fe ₂ O ₄ (M: Mn, F
e, Co, Ni, Cu, Zn, Mg) ferrite powder in a temperature range of 200 to 1000 ° C. and a sintering pressure of 50 to
A ferrite sintered body for giant magnetoresistive effect material, characterized by being sintered under the condition of 300 MPa. 6. The ferrite sintered body for giant magnetoresistive material according to claim 5, wherein the surface insulating layer is a Fe ₂ O ₃ insulating layer formed by heat treatment or an insulating layer formed of an insulating organic material. 7. The average particle size of an insulating layer formed on the surface is 10
nm-700 nm of M · Fe ₂ O ₄ (M: Mn, F
e, Co, Ni, Cu, Zn, Mg) A sintered body using a ferrite powder is embedded in a soft magnetic body, or
A bulk magnetoresistive element characterized by being combined by laminating the soft magnetic material . 8. The soft magnetic material has a coercive force of 10 Oe or less.
The bulk magnetoresistive element according to claim 7, which is a bulk soft magnetic material having a magnetic permeability of 10 ³ or more . 9. The surface insulating layer is made of Fe ₂ O ₃ by heat treatment.
9. The bulk magnetoresistive element according to claim 7, which is an insulating layer or an insulating layer made of an insulating organic material.