JP2001203409A - Method of manufacturing magnetoresistance effect element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a granular structure, in which fine particles of a manganese oxide in which part of the La site of LaMnO3 having a new perovskite structure is replaced with Ca or Sr are embedded in a nonmagnetic insulator matrix, and in addition, a gigantic magnetoresistance effect element using the granular structure. SOLUTION: In the method of manufacturing the granular structure in which fine particles of a ferromagnetic oxide are scattered in a matrix of a nonmagnetic insulator, perovskite type LaMnO3, in which part of La site is replaced with Sr or Ca, is used as the ferromagnetic insulator. The method includes at least a step (1) of forming a polycrystalline LaMnO3 thin film on a nonmagnetic insulator substrate, a step (2) of forming island-like thin films, which do not come into contact with each other by selectively removing the grain boundaries of the thin film, and a step (3) of forming a nonmagnetic insulating film on the substrate to cover the island-like thin films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a granular structure in which a manganese oxide in which a La site of LaMnO ₃ having a perovskite structure is partially substituted with Ca or Sr is dispersed as fine particles in a nonmagnetic insulating film. Further, the present invention relates to a magnetoresistive element using the granular structure.

[0002]

2. Description of the Related Art Conventionally, metallic magnetic materials, mainly permalloy, have been used for magnetic thin films of magnetic sensors and thin film magnetic heads utilizing the magnetoresistance effect (hereinafter referred to as MR). Such an MR element utilizes a difference in resistance effect generated depending on a relative angle between a current direction of Permalloy and a direction of magnetization. However, a material having a large magnetoresistance change rate has been demanded for a high sensitivity because the magnetoresistance change rate is as small as about several percent.

[0003] In recent years, a material having a much higher magnetoresistance change rate than ever before has been found in a metal system. This large change in magnetoresistance is referred to as a giant magnetoresistance effect (hereinafter referred to as GMR), and a super giant magnetoresistance effect has recently been discovered even in oxides. In particular, Mn-based oxide L
In a perovskite-type oxide composed of a-Sr-Mn-O, a large magnetoresistance change is observed that is not observed with permalloy and metal. The reason why the giant magnetoresistance effect seen in oxides occurs is not yet clear, but due to the structural phase transition that occurs when a magnetic field is applied,
It is considered that the electrical resistance changes greatly.

As described above, an oxide having a magnetoresistive effect exhibits an extremely large magnetoresistance change rate as compared with a conventional metal material such as permalloy. The head element can be manufactured at a higher density and more compactly.

Further, it is also known that oxides having a magnetoresistive effect change not only a magnetic field but also physical characteristics such as electric resistance due to stimulation of light, electric charge and the like. Therefore, oxides having a magnetoresistive effect are expected to be applied not only to memories and magnetic heads but also to a wide range of industrial fields.

Among oxides having a magnetoresistance effect, L
Perovskite-type oxides having a composition in which a part of the La site of aMnO ₃ is substituted with Sr or Ca have been actively studied. Attention has been paid not only to single crystals of this oxide but also to polycrystals, and research has begun.

For example, Applied Physics Letters Vol. 77, (1996) 2041-2044, {App
l. Phys. Lett., Vo177 (1996) 2
As shown in FIG. 041-2044 °, this magnetoresistance effect is considered to be caused by a ferromagnetic tunnel junction having a grain boundary as a tunnel barrier.

In general, in a single tunnel process, the resistance of the tunnel process is R, the change in resistance due to magnetism is ΔR, and the spin polarizabilities of the first magnetic material and the second magnetic material are P _l and P, respectively. When _2, the magnetoresistance _{ratio, △ R / R = 2P 2} P 1 / (1-P 1 P 2) be represented by (1) it has been known. It can be seen from this equation that the larger the spin polarizability, the higher the magnetoresistance change.

A tunnel type magnetoresistive element using a perovskite type Mn oxide ferromagnetic material having a large spin polarizability has been reported. For example, Applied Physics Letters Vol. 69, (1996) 3266-326
8, {Appl. Phys. Lett. , VO177
(1996) 3266-3268}, La _O.67 Sr
_{O. 33 MnO 3 / SrTiO 3 /} La O.67 Sr O.33 MnO 3
It is known that a device having a structure can obtain a large magnetoresistance effect. As described above, if the manganese oxide in which the La site of LaMnO ₃ having a perovskite structure with large spin polarization is partially substituted with Ca or Sr is used for the ferromagnetic metal layer, the transition metal ferromagnetic A much higher magnetoresistance ratio than that obtained with a tunnel junction can be expected.

As such a system, a granular structure in which magnetic particles are dispersed at a high density in an insulating matrix so that the particles do not directly contact each other has attracted attention. For example, Journal of Applied Physics Vol. 82, (1997) 5646-56-52,
{J. App1. Phys. , VO182 (1997)
5646-5652} shows a Co-Al-O-based thin film which is a transition metal-based granular thin film. In this example, the transition metal is used as the magnetic particles, but if this is a manganese oxide in which part of the La site of LaMnO ₃ having a perovskite structure is substituted with Ca or Sr, a larger magnetoresistance change rate is obtained. Can be expected. In order to produce a device such as a magnetic sensor or a magnetic memory utilizing the magnetoresistance effect, it is desired that a large magnetoresistance change occurs even under a low magnetic field. As such a material, a granular structure material of a perovskite oxide, which can be expected to have a large magnetoresistance effect by a higher-order tunnel effect, is promising.

[0011]

However, it has been more difficult to produce a granular structure of perovskite oxide as compared with a metallic granular structure.

Therefore, the present invention provides a novel granular structure of LaMnO ₃ having a perovskite structure, in which fine particles of manganese oxide in which La sites are partially substituted with Ca or Sr are embedded in a nonmagnetic insulator matrix. It is an object of the present invention to propose a manufacturing method and a magnetoresistive element using this granular structure.

[0013]

According to the present invention, there is provided a method for producing a granular structure in which fine particles made of a ferromagnetic oxide are dispersed in a matrix made of a nonmagnetic insulator. Having
LaMnO ₃ , wherein La _{1 -X} Ca _X MnO ₃ (X ≠ 0) in which part of the La site of LaMnO ₃ is substituted by Ca, or La _1- in which part of the La site is substituted by Sr (1) a step of forming a polycrystalline thin film of the ferromagnetic oxide on a nonmagnetic insulator substrate using a material having any composition of _Y Sr _Y MnO ₃ (Y ≠ 0); A) a step of selectively removing grain boundaries of the polycrystalline thin film to form the polycrystalline thin film into an island shape on the substrate which does not contact each other; and (3) a polycrystalline thin film formed into an island shape by the step (2). Forming a non-magnetic insulating film on the substrate to cover
A method for forming a granular structure of a ferromagnetic oxide having a magnetoresistive effect having at least the following is proposed.

The ferromagnetic oxide of the present invention (part of the La site
Perovskite LaMnO ₃ substituted with Sr or Ca)
By using a magneto-resistive element with a granular structure dispersed in a non-magnetic insulating film as fine particles in devices such as magnetic sensors and magnetic memories, it is possible to produce a large change in magneto-resistance even under low magnetic field conditions. It has become possible.

Further, the magnetoresistive element using the granular structure of the present invention makes it possible to obtain a higher rate of change in magnetic resistance than a conventional magnetoresistive element with a compact magnetoresistive element.

The substrate for forming a ferromagnetic oxide film according to the present invention is a perovskite-type LaMnO in which a part of La site is substituted by Sr or Ca in view of lattice matching.
_A non-magnetic insulator having a lattice constant of 20% or less at the junction surface with ₃ is preferably used. More preferably, the nonmagnetic insulator has a lattice constant of 5% or less at the bonding surface.
For example, as a substrate having a lattice constant of 5% or less, SrTi
O ₃ , LaAlO _{3 and the} like are preferably used.

Further, the non-magnetic insulating film of the step (3) covers the island-shaped ferromagnetic oxide thin film and the substrate surface and acts as a tunnel layer, so that the leakage current is small.
The material is not particularly limited as long as it has a high withstand voltage.

By partially substituting the La site of LaMnO ₃ with Ca or Sr, a ferromagnetic material can be obtained. La _1-X Ca _X
In MnO ₃ (X ≠ 0) and La _1-Y Sr _Y MnO ₃ (Y ≠ 0), the preferable composition range is preferably 0.1 or more and 0.5 or less for both X and Y. More preferably, it is not less than 0.15 and not more than 0.4. When X and Y are in this range, a sufficiently large magnetoresistance effect element can be obtained.

Sr and Ca are La and Ca during the formation of the ferromagnetic oxide thin film.
It is common to dope at the same time. As a film formation method, a sputtering method using a target whose composition is adjusted, a sol-gel method, a laser ablation method, or the like is used.

By annealing a ferromagnetic oxide thin film formed by a sputtering method and a laser ablation method at an appropriate temperature, a granular structure exhibiting a greater magnetoresistance effect can be obtained. At this time, the crystal grains of the ferromagnetic oxide grow while inheriting the crystal orientation direction of the substrate surface, and thus the obtained oxide crystal grains are uniaxially oriented.

Factors such as the temperature, time, and atmosphere of the annealing greatly affect the crystal grain growth of the ferromagnetic oxide thin film.

The annealing temperature is desirably 700 ° C. or higher. When annealing is performed under these conditions, a greater magnetoresistance effect can be obtained.

The annealing time should be determined in consideration of the annealing temperature and the film thickness.
Generally, the higher the annealing temperature and the thinner the film thickness, the shorter the tendency.

For example, when annealing a ferromagnetic oxide thin film having a thickness of 10 nm at an annealing temperature of 700 ° C., 1
It is desirable to perform annealing for 0 to 20 minutes.

The annealing is preferably performed in the air or in an oxygen atmosphere. It is known that by performing annealing in such an atmosphere, a stronger magnetoresistance effect can be obtained.

When the ferromagnetic oxide thin film is formed by the sol-gel method, a high-temperature sintering process is included, so that it is not necessary to perform annealing in this case.

Preferably, the ferromagnetic oxide is a polycrystal, and the crystal axis of the polycrystal is uniaxially oriented.

If the crystal axes of the ferromagnetic oxide film are aligned in a certain direction, the variation in the etching rate of the crystal grain surface (not the grain boundary) during the selective etching of the grain boundary performed in a later step becomes small. Therefore, it becomes easy to selectively remove only the crystal grain boundaries.

The thickness of the ferromagnetic oxide thin film is one of the factors that influence the crystal grain size. If the steps after film formation are the same, the crystal grains tend to be larger as the film thickness is larger. According to the study of the present inventors, a film thickness of 5 to 10 nm is the easiest to work for forming a granular structure.

In this way, when the polycrystalline ferromagnetic oxide thin film is completed on the substrate, the crystal grain boundaries are selectively removed to separate the ferromagnetic oxide thin film for each crystal grain. The islands do not touch each other. The etching method used at this time can be suitably selected from methods in which the etching rate at the crystal grain boundary is higher than the etching rate at the crystal grain surface.

Specifically, dry etching using plasma of CF ₄ , Cl ₂ or the like can be mentioned. However, chemical etching using an acidic solution which can process a large number of substrates at once without requiring any special apparatus seems to be most suitable.

As the acidic solution used for etching, HF and HC having selective etching properties with respect to crystal grain boundaries are used.
It is desirable to use l, HNO ₃ , H ₃ PO ₄ , NH ₄ Cl, etc. as an aqueous solution, alone or as a mixture.

Since the concentration of the etching solution and the temperature at which the etching is performed have a great influence on the etching rate at the crystal grain boundaries, it is desirable to determine the concentration by conducting sufficient preliminary experiments.

It is desirable that the polycrystalline oxide film is immersed in the etching solution prepared as described above to perform the etching, and that the point where the crystal grains are separated be the end point of the etching. Specifically, it is desirable that the point at which the interval between crystal grains becomes 1 to 5 nm be the etching end point.

The spacing between crystal grains has a close relationship with the tunnel effect that appears. If the spacing between crystal grains is 5 nm or less, the tunnel effect occurs with a practically acceptable probability. If the spacing between crystal grains is 1 nm or more, a tunnel effect occurs with a very high probability, so that a large magnetoresistance effect can be obtained.

After obtaining a substrate having island-shaped oxide crystal grains not in contact with each other, the crystal grain surface is then
The substrate exposed in the gap between the crystal grains is covered with a non-magnetic insulating film. The material of the non-magnetic insulating film at this time is not particularly limited as long as it is non-magnetic and an insulating substance.
Al ₂ O ₃ , SiO ₂ and SrTiO ₃ are preferably used.

However, in order for one electron to repeat the tunnel phenomenon two or more times to enhance the magnetoresistance effect, the island of the ferromagnetic oxide needs to be completely covered with the nonmagnetic insulating film. is there. For this reason, it is desirable that the nonmagnetic insulating film covering the surface of the crystal grains and the surface of the substrate exposed in the gap between the crystal grains is formed sufficiently thicker than the height of the crystal grains.

The present invention also provides a granular thin film formed by the above-described method, and a magnetoresistive element using the granular thin film.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic diagram of a method for producing a ferromagnetic oxide thin film having a magnetoresistance effect.

First, a ferromagnetic oxide thin film 2 made of a manganese oxide in which part of La sites of LaMnO ₃ having a perovskite structure is substituted with Ca or Sr is formed on a substrate 1 made of a nonmagnetic oxide ( FIG. 1 (a)). A known method such as a sputtering method, a laser absorption method, or a sol-gel method can be used for forming the ferromagnetic oxide thin film 2. The thickness of the ferromagnetic oxide thin film 2 is preferably in the range of 1 to 10 nm.

Since the granular structure is a structure in which fine particles of a ferromagnetic substance are dispersed in a nonmagnetic insulating film matrix, the substrate 1 on which the ferromagnetic oxide thin film 2 is formed must be a nonmagnetic insulating material. Must. Further, it is desirable to use a crystal whose lattice constant at the junction surface between the substrate 1 and the ferromagnetic oxide thin film 2 differs from the ferromagnetic oxide thin film by at least 20% or less. If the lattice constant at the junction surface with the ferromagnetic oxide thin film 2 is within 20%, the orientation of the ferromagnetic oxide thin film 2 is not significantly impaired.

When the ferromagnetic oxide thin film 2 is formed by a sputtering method or a laser absorption method, the ferromagnetic oxide thin film 2 is annealed to orient the crystal in one direction. The annealing temperature at this time largely depends on the thickness of the ferromagnetic oxide thin film 2, but is preferably at least 700 ° C. or more.

When the ferromagnetic oxide thin film 2 is formed by the sol-gel method, the film is sintered at a high temperature after the film formation, so that the annealing operation is unnecessary.

Subsequently, the ferromagnetic oxide thin film 2 in a mosaic shape in which a number of crystal grains are separated by grain boundaries is immersed in the acidic solution 3 together with the substrate 1. In the etching with the acidic solution 3, since the etching speed of the grain boundary is higher than that of the surface of the crystal grain, the grain boundary expands right and left, and the crystal grains finally separate from each other. Thus, island-like ferromagnetic oxides 4 separated from each other are formed on the substrate 1 (FIG. 1B).

Finally, the island ferromagnetic oxide 4 is covered with a non-magnetic insulating film 5. The material used for the non-magnetic insulating film 5 is not limited except that it has no magnetism and is insulative. It can be arbitrarily selected from known materials.
However, since the non-magnetic insulating film 5 must completely cover the island-shaped ferromagnetic oxide film, it is desirable that the non-magnetic insulating film 5 be deposited sufficiently thick (FIG. 1C).

The substrate 1 may be any substrate as long as it exhibits resistance to high temperatures and acidic solutions 3 required for producing a ferromagnetic oxide thin film and the ferromagnetic oxide thin film 2 exhibits a magnetoresistance effect. In particular, it is desirable to use a substrate having a lattice constant deviation of 20% or less at the junction surface between the substrate 1 and the ferromagnetic oxide thin film 2. More preferably, the substrate has a lattice constant deviation of 5% or less.

The method for forming the ferromagnetic oxide thin film 2 is as follows.
A sbutter method, a sol-gel method, a laser ablation method, or the like is used.

In order to obtain a uniaxially oriented polycrystalline ferromagnetic oxide, it is very effective to perform annealing after forming the ferromagnetic oxide thin film. The annealing temperature is desirably 700 ° C. or higher as described above. The annealing is preferably performed in an atmosphere containing oxygen so that the composition of the ferromagnetic oxide film does not change. For example, it is desirable to perform annealing in the air or oxygen at 1 atm. As a result, the ferromagnetic oxide thin film
A polycrystalline ferromagnetic oxide polycrystal uniaxially oriented is obtained. The acidic solution 3 is not particularly limited as long as it can selectively etch the grain boundary portion of the ferromagnetic oxide thin film 2.
For example, HF, HCl, HNO ₃ , H ₃ PO ₄ , NH ₄ Cl
And mixed solutions thereof.

As the nonmagnetic insulating film 5, for example, A1
₂ O ₃ , SiO ₂ , and SrTiO ₃ are selected in consideration of lattice matching with the substrate and the island-shaped ferromagnetic oxide 4. As a film forming method, a sbutter method, a sol-gel method, a laser ablation method, or the like is used.

If the island-shaped ferromagnetic oxide 4 is not completely covered with the non-magnetic insulating material, the granular structure cannot exhibit its effect. It is desirable that the film be formed to have a film thickness that completely covers the film.

In order to obtain a magnetoresistive effect element using this granular thin film, the electrode 9 may be provided on the ferromagnetic oxide thin film as shown in FIG.

The electrode is not particularly limited as long as it is a metal or metal oxide having conductivity. For example, A
g, Pt, Au, Cu, Al, Ti, Ta, Si and alloys thereof, or TiN, IrO ₂ , RuO _{2 and the} like.

[0053]

EXAMPLES Examples are shown below as an example of the above-mentioned manufacturing method.

Embodiment 1 FIG. 2 shows a flow of a method of manufacturing a ferromagnetic oxide thin film having a granular structure according to the present embodiment. SrTiO ₃ (100) was used as the substrate 7. The deviation of the lattice constant between the substrate and the ferromagnetic oxide thin film is 1
% Or less.

A ferromagnetic oxide thin film 8 was formed by sputtering using a sintered body of La _0.8 Sr _0.2 MnO ₃ as a target (FIG. 2A). The substrate temperature during film formation is 700
C. and the sputtering time was 30 minutes. The thickness of this ferromagnetic oxide thin film was 10 nm as confirmed by cross-sectional SEM. This ferromagnetic oxide thin film was annealed at 700 ° C. for 20 minutes in an oxygen atmosphere at atmospheric pressure.

The composition analysis of this ferromagnetic oxide thin film by inductively coupled high frequency plasma spectroscopy (ICP-MASS) confirmed that a ferromagnetic oxide thin film equivalent to the composition of the sputtering target was formed. Was.

The precision of the ferromagnetic oxide thin film is
As a result of X-ray analysis, only a peak corresponding to one axis was detected, and it was confirmed that the ferromagnetic oxide thin film was oriented in one axis.

Thereafter, by a known lithography method,
An electrode 9 was formed by depositing 30 nm of Pt on a predetermined position of the ferromagnetic oxide thin film by molecular beam sputtering (MBS). The distance between the electrodes is 1 mm (FIG. 2 (b)). The produced electrode 9 was covered with a photoresist 10 by a known method (FIG. 2C). Subsequently, the entire substrate was heated to a liquid temperature of 25.
The substrate was immersed in a 0.1 mol / l HCl aqueous solution at 1 ° C. for 1 minute to remove crystal grain boundaries to obtain an island-like ferromagnetic oxide 11 (FIG. 2).
(d)).

It was confirmed by SEM observation that the obtained island-like ferromagnetic oxide 11 had a circular island portion of 10 nm to 50 nm and a gap between the islands of 1 to 10 nm.

Also, as far as the SEM observation was concerned, the film thickness of the island-shaped ferromagnetic oxide 11 did not seem to change substantially.

Thereafter, the substrate was immersed in a stripping solution, and the photoresist for protecting the electrodes was removed (FIG. 2 (e)). Next, the electrode portion is covered with a mask, and a gap between the island-shaped ferromagnetic oxide thin film and the island-shaped ferromagnetic oxide thin film is filled with S, which is the same material as the substrate.
rTiO ₃ was formed by sputtering at a substrate temperature of 700 ° C. for 60 minutes. The film thickness of SrTiO ₃ deposited at this time is
100 nm.

Thus, the island-shaped ferromagnetic oxide thin film is embedded in the SrTiO ₃ matrix which is a non-magnetic insulating film. Finally, a heat treatment was performed at 600 ° C. for 15 minutes in an oxygen stream to form a nonmagnetic insulating film 12, thereby obtaining a desired granular film and a magnetoresistive element (FIG. 2 (f)).

[0063] As a result of measurement of magnetic resistance change rate of the magnetoresistive element produced in this way _{(△ R / R O),} 1
When a magnetic field of 000 Oe or less was applied, the maximum value was as large as -20%.

<Embodiment 2> FIG. 2 shows a flow of a method of manufacturing a ferromagnetic oxide thin film having a granular structure according to this embodiment. LaAlO ₃ (100) was used as the substrate 7. La _0.7 Ca _0.3 MnO ₃ is deposited on the substrate by sputtering.
Oxide thin film 8 using a sintered body of
Was formed. The substrate temperature during film formation was 750 ° C., and the sputtering time was 45 minutes. 700 ° C.
For 20 minutes in an oxygen atmosphere at atmospheric pressure. The thickness of the ferromagnetic oxide thin film was 10 nm, which was observed by a cross-sectional SEM. Thereafter, Pt was deposited to a thickness of 30 nm on the surface of the ferromagnetic oxide thin film by molecular beam sputtering (MBS) to form an electrode 9. After covering the produced electrode 9 with a photoresist 10, etching was performed for 1 minute in a 0.5 mol / l HNO ₃ aqueous solution at 25 ° C. to selectively remove the grain boundary portion and remove the island-like ferromagnetic oxide 11. I got At this time, the island-like ferromagnetic oxide 11 shows that
It was confirmed that the island portion had a circular shape of 10 to 50 nm, and the gap between the islands was 1 to 10 nm. Then, it was immersed in a stripping solution to remove the photoresist.

Next, the electrode portion is covered with a mask, and a SiO ₂ film, which is a nonmagnetic insulating film 12, is sputtered on the island-like ferromagnetic oxide thin film at a substrate temperature of 80 ° C. for 40 minutes.
A target granular film and a magnetoresistive element were formed with a thickness of 00 nm.

[0066] As a result of measurement of magnetic resistance change rate of the magnetoresistive element produced in this way _{(△ R / R O),} 1
When applied with a magnetic field of 000 Oe or less, the maximum value was as large as -15%.

[0067]

According to the present invention, a granular structure is formed when crystal grains of manganese oxide in which a part of La site of LaMnO ₃ having a perovskite structure is substituted by Ca or Sr are dispersed in a nonmagnetic insulator matrix. I was able to.

Further, a magnetoresistance effect element using a granular structure produced by the production method of the present invention was produced. The magnetoresistive element thus obtained exhibited a higher magnetoresistance change rate than the conventional method, and a large magnetoresistance change occurred even in a low magnetic field.

[Brief description of the drawings]

FIG. 1 illustrates a method for manufacturing a magnetoresistance effect element used in an embodiment.

FIG. 2 illustrates a method for manufacturing a magnetoresistance effect element.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 ferromagnetic oxide thin film 3 acidic solution 4 island-like ferromagnetic oxide 5 nonmagnetic insulating film 6 granular thin film 7 substrate 8 ferromagnetic oxide thin film 9 electrode 10 photoresist 11 island-like ferromagnetic oxide 12 nonmagnetic insulating film

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryoji Fujiwara 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term (reference) in Canon Inc. 5E049 AB10 AC00 AC05 BA12 BA16

Claims (4)

[Claims] 1. A method for producing a granular structure in which fine particles made of a ferromagnetic oxide are dispersed in a matrix made of a nonmagnetic insulator, wherein the ferromagnetic oxide is LaMnO ₃ having a perovskite structure, La _1-X Ca _X MnO in which part of the La site of LaMnO ₃ is substituted by Ca
₃ (X ≠ 0) or part of La site was replaced by Sr
(1) a step of forming a polycrystalline thin film of the ferromagnetic oxide on a non-magnetic insulating substrate by using one having a composition of La _1-Y Sr _Y MnO ₃ (Y ≠ 0); (2) a step of selectively removing grain boundaries of the polycrystalline thin film and forming the polycrystalline thin film on the substrate in an island shape that does not contact each other; and (3) forming an island shape by the step (2). Forming a non-magnetic insulating film on the substrate so as to cover the polycrystalline thin film, the method comprising: forming a granular structure of a ferromagnetic oxide having a magnetoresistance effect; 2. The method for producing a granular structure of a ferromagnetic oxide having a magnetoresistance effect according to claim 1, wherein the ferromagnetic oxide is a polycrystal, and a crystal axis of the polycrystal is uniaxially oriented. . 3. A granular thin film produced by the method according to claim 1. 4. A magnetoresistive element using the granular structure thin film according to claim 3.