JPH08147639A - Magnetoresistance film and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a magnetoresistance film in which the change rate of magnetoresistance is large compared to a change in a very small magnetic field. CONSTITUTION: A magnetoresistance multilayer film in which ferromagnetic layers 1 and nonferromagnetic layers 2 are formed alternately and in which the ferromagnetic layers 1 are made discontinuous by a heat treatment has a structure in which an interface on the side far from a substrate 3 as viewed from the nonferromagnetic layers 2 is made flatter than an interface on the side close to the substrate 3. Thereby, the performance of a magnetic recording apparatus can be enhanced remarkably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording device such as a magnetic disk, and more particularly to an information reading portion having high detection sensitivity.

[0002]

2. Description of the Related Art The greatest problem in a magnetic recording device such as a magnetic disk is to increase the recording density, and with this, a magnetic head using a magnetoresistive effect that enables improvement of read performance of recorded information. Development is in progress.

The magnetoresistive effect is a phenomenon in which the electric resistance value changes when a magnetic field is applied to a ferromagnetic thin film. To read the recorded information by using this phenomenon, the leakage magnetic field from the magnetic recording medium is guided to the magnetoresistive effect film, the direction of the magnetization of this film is changed, and the change of the electric resistance value is detected. Therefore, the larger the change in the electric resistance value with respect to the change in the magnetic field, the larger the signal-to-noise ratio and the better the characteristics.

Conventionally, a thin film of permalloy or the like has been used as a thin film which produces the magnetoresistive effect, but the rate of change in resistance depending on the presence or absence of a magnetic field application is 4% at most. An attempt to increase this rate of change was made by Journal of Magnetics and Magnetic Materials No. 94.
Volume, pages L1-L5 (Journal of Magnetism and Magn
etic Materials Vol.94, p. L1-L5), a multilayer film in which 15 Å-thick cobalt thin layers and 9 Å-thick copper thin layers are alternately laminated has been reported to have a magnetoresistance change rate of 48%.

However, this film has a problem that the detection sensitivity is low. That is, the magnetic field required to change the magnetic resistance was large, and a magnetic field as large as 4000 Oersted (hereinafter referred to as Oe) was required to obtain the resistance change rate. In this multilayer film, the difference in electrical resistance between the case where the magnetizations of the adjacent ferromagnetic layers are parallel and the case where the magnetizations are antiparallel is used. However, this antiparallel interaction is approximately 4000 in terms of magnetic field.
It is strong with Oe and requires a large magnetic field to shift from the antiparallel state to the parallel state. In order to read recorded information with a magnetic head of a magnetic recording device such as a magnetic disk, it is necessary to operate with a magnetic field of several tens Oe, and therefore the film cannot be immediately used for the magnetic head.

A multi-layer film with improved detection sensitivity is described in Science Vol. 261, 1021-1024 (Science,
Vol. 261, p. 1021-1024, (1993)) is a film made of permalloy (NiFe) and silver (Ag). This is 2 nm thick NiFe and 4 nm thick A
g is alternately laminated and heat-treated at a temperature of about 315 ° C. In this film, by heat treatment, NiF
Ag penetrates into the grain boundaries of the e layer, and the NiFe layer 1 is divided and becomes discontinuous, as schematically shown in FIG. In such a structure, as shown by + and − marks in FIG.
A magnetic pole is generated at the end of the NiFe grain, and when no external magnetic field is present, the magnetization of each crystal grain is parallel and the magnetization of the adjacent NiFe layer is antiparallel within the same layer.
That is, antiferromagnetic coupling works between adjacent NiFe layers.

The antiferromagnetic coupling is important in the magnetoresistive effect multilayer film, and in this film, it is brought about by the magnetostatic coupling between the ferromagnetic layers. When a sufficient magnetic field is applied from the outside, the magnetizations of the adjacent NiFe layers become parallel. Similar to the above-mentioned multilayer film made of cobalt and copper, there is a large difference in electric resistance between the magnetizations of the adjacent NiFe layers being parallel and antiparallel, and this property is used for detection of magnetic recording. The magnetostatic interaction here between the adjacent ferromagnetic layers is
S electron and d generated in the above-mentioned multilayer film of cobalt and copper
It is smaller than the coupling between ferromagnetic layers due to the interaction of electrons. Therefore, the magnetic field required to change the electrical resistance is small,
A resistance change rate of 4 to 6% is obtained for a magnetic field of about 10 Oe.

[0008]

As described above, this N
The iFe / Ag multilayer film can obtain higher sensitivity than the conventional magnetoresistive multilayer film, but in order to dramatically increase the density, it is also necessary to improve the absolute value of the magnetoresistive change rate. Generally, in order to increase the rate of change in magnetoresistance in a magnetoresistive multilayer film, it is effective to increase the number of laminated layers. This is because the number of times that conduction electrons cross the interface between the ferromagnetic layer and the non-ferromagnetic layer, which is necessary for changing the magnetoresistance, increases.

However, in the NiFe / Ag multilayer film, the magnetoresistance change rate is saturated when the number of NiFe layers is about 5, as described in the known example. That is, there is a problem that the magnetoresistance change rate does not increase even if the number of stacked layers is increased.

The problem to be solved by the present invention is to alleviate the problem that the magnetoresistive change rate does not increase even if the number of laminated layers is increased, and the sensitivity is higher than that of the multilayer film shown in the known example. The present invention provides a magnetoresistive film and applies it to a magnetic head and a magnetic recording device.

[0011]

A multilayer film in which thin layers of a ferromagnetic metal and thin layers of a non-ferromagnetic metal are alternately laminated, particularly a multilayer film in which a ferromagnetic layer is divided by a non-magnetic substance The above object is achieved by forming a structure in which the interface farther from the substrate is flatter than the interface closer to the substrate when viewed from the non-ferromagnetic layer.

[0012]

In the NiFe / Ag multilayer film, the above-mentioned problem that the magnetoresistance change rate does not increase even if the number of layers is increased is
From an electron microscopic observation of the cross section of the film, it was found that the cause was the contact between adjacent NiFe layers. In the actual film, unlike the principle diagram of FIG. 2, the unevenness of each layer is large as shown in FIG. When the NiFe layer thickness is 2 nm and the Ag layer thickness is 4 nm, when the number of NiFe layers is about 1 to 2, this NiFe layer
No layer contact is seen, but as the number of NiFe layers increases,
In the region far from the substrate, contact of the NiFe layer partially occurs, as schematically shown in regions A and B of FIG.

As described above, in order for the magnetoresistance to change, it is necessary that the magnetization directions of the adjacent NiFe layers be antiparallel when no magnetic field is applied. Since the magnetization directions of the NiFe crystal grains are parallel, this region does not contribute to the change in magnetoresistance.
When the number of layers is further increased, the contact of this NiFe layer is further increased as the distance from the substrate is increased.

In the magnetoresistive effect multilayer film using the interaction between the ferromagnetic layers based on the interaction between the s-electron and the d-electron, the rate of change in magnetoresistance is proportional to the number of layers or increases faster than proportionally. Therefore, even in this NiFe / Ag multilayer film, it is considered to be the same if there is no contact with the NiFe layer. However, in reality, even if the number of layers is increased, the contact area of the NiFe layers does not increase the region that contributes to the change in magnetoresistance, so that the rate of change in magnetoresistance is saturated.

Further, when the cross-sectional structure was observed in detail, it was found that the contact of the NiFe layer occurred in a portion where the unevenness of the layer was large. That is, the size of this unevenness and Ni
The degree of contact of the Fe layer corresponds to the magnitude. And
The unevenness tends to increase as the distance from the substrate increases. Therefore, by increasing the number of layers and forming a structure in which the unevenness of the layers does not increase even in the region far from the substrate, such contact of the NiFe layer can be suppressed.

As shown in FIG. 1, when a film is formed in which the interface on the side far from the substrate has a higher flatness than the interface on the side closer to the substrate as shown in FIG. 1, the unevenness of the NiFe layer increases as the distance from the substrate increases. This tendency is relaxed, and adjacent Ni
The contact of the Fe layer is suppressed. As a result, even if the number of layers is increased, the saturation tendency of the magnetoresistance change rate is relaxed, and a large magnetoresistance change rate can be obtained.

[0017]

EXAMPLES As described above, in the Ag layer, a state in which the interface farther from the substrate has higher flatness than the interface closer to the substrate needs to be obtained after the heat treatment. Generally, the fine structure of the film is changed by the heat treatment, and the Ag layer also has the property of easily rounding the Ag crystal grains by the heat treatment, and as a result, the surface (interface) of the Ag layer tends to have irregularities. Therefore, before the heat treatment, that is, immediately after the film is formed, the interface of the Ag layer on the side far from the substrate needs to be as flat as possible. Therefore, in this embodiment, the film formation is performed by using the sputter / etching together with the ordinary sputter film formation.

As shown in FIG. 4A, a Ta layer 4 as a base layer 4 is first formed on the Si substrate 3. Ta with a thickness of 7 nm was formed by a sputtering method with Ar pressure set to 0.7 mTorr.
A film was formed. As described above, since it is more effective to increase the flatness from the stage of the underlayer, as shown in FIG.
The a layer 4 was flattened. The etching rate in sputter etching depends on the incident angle of Ar ions, is the smallest at the incidence perpendicular to the plane, and increases as the inclination increases. For this reason, when Ar ions are irradiated perpendicularly to the substrate surface, many convex portions are etched, and thus the surface flatness is improved. The sputter etching has a Ta layer thickness of 5
It carried out until it became nm.

Next, as shown in FIG. 4C, an Ag layer is deposited on the Ta layer. Generally, since the Ag film has poor flatness, the target layer thickness after sputter etching is 2 nm,
A 4 nm Ag layer 2 was formed by sputtering. When the Ag layer thickness is reduced to 2 nm by the sputter etching, as shown in FIG.
As shown in (d), the unevenness was reduced to a level where it was almost undetectable. On top of this, as shown in FIG.
The e-layer 1 was formed by sputtering.

In the magnetoresistive effect multilayer film using magnetostatic coupling between the ferromagnetic layers, which is treated in the present invention, it is important that the ferromagnetic layers are discontinuous. This is realized when the layers have irregularities. Since it is easy, the NiFe layer is not flattened by sputter etching.

Then, as shown in FIG. 4 (f), the NiFe
An Ag layer 2 is further formed on the layer 1. At this time, after forming a film by sputtering to a thickness of 8 nm, the film was sputter-etched as shown in FIG.

The surface of the Ag layer 2 of the second layer (the interface on the side far from the substrate when the entire film is formed)
It was possible to reduce the unevenness of the to a negligible extent. Although not shown below, a NiFe layer having a thickness of 2 nm and an Ag layer having a thickness of 4 nm were sequentially and alternately formed thereon by the same method. 10 nm as a protective film on the surface of the film
Thick Ta was deposited.

The film thus formed was heat-treated at 320 ° C. for 30 minutes. Examining the cross-sectional structure of the heat-treated film, the flatness is inferior to that of the film before the heat treatment, but compared to the film formed without performing the flattening treatment by sputtering / etching, FIG. As shown, the flatness of the interface of the Ag layer on the side far from the substrate is overwhelmingly high. This significantly reduced the contact between adjacent NiFe layers.

The magnetoresistance change rate after heat treatment of the magnetic film according to the present invention is shown in FIG. 5 as a function of the number of NiFe layers. The applied magnetic field is 15 Oe. As is clear from the figure, Ni
Even if the number of Fe layers is 20, it is not saturated and the number of NiFe layers is 2
In the case of 0, a magnetoresistance change rate of 10.7% was obtained.

In this embodiment, sputtering film formation and sputtering
Although the film was formed by using the etching together, as is clear from this principle, the same effect can be obtained by flattening the layer by using the vacuum evaporation method together with the sputter etching. Also,
The Ag layer may be formed by sputtering while applying a negative potential to the substrate without performing sputtering / etching. This is because when a negative potential is applied to the substrate during sputtering, argon ions accelerated by the negative potential collide with the film surface,
This is because etching is performed at the same time as the film formation to form an Ag layer having good flatness. Also by this method, an effect similar to that obtained when sputtering and etching were performed independently was obtained.

In the examples, the NiFe / Ag multilayer film was described in detail, but the present invention is also effective for the magnetoresistive multilayer film in which other substances are combined. Co / Ag, Fe /
The characteristics of a ferromagnetic layer having a discontinuous structure obtained by heat-treating a multilayer film of Ag and Ni / Ag were examined, and when the number of ferromagnetic layers was 20, magnetic properties of 18%, 14% and 6% were obtained. The rate of resistance change was obtained.

Further, although the film having the structure in which the ferromagnetic layer is discontinuous has been described, even in the film having the continuous ferromagnetic layer, the magnetoresistance change rate is improved by forming the film in which the non-ferromagnetic layer is flattened. did. For example, a film obtained by stacking 20 cycles of 1 nm thick NiFe and 1 nm thick Cu and having a magnetoresistance change rate of 15%.
From 18%. This is considered to be because the change in resistivity Δρ does not change, but the flatness decreases the resistivity ρ and increases the magnetoresistance change rate Δρ / ρ.

A magnetic head was manufactured using the NiFe / Ag magnetoresistive film shown in the examples. A perspective view of the magnetic head is shown in FIG. An electrode 12 is provided on the multilayer magnetoresistive film 11 described in the embodiment, and further, a permanent magnet layer 13 is opposed to the insulating layer 14 made of Al ₂ O _{3 so as} to sandwich it. This permanent magnet layer is for applying a bias to the multi-layered magnetoresistive effect film 11.
% Pt layer was used. And these are arrange | positioned in the area | region pinched by the two shield layers 15 of a NiFe alloy. The thickness of each layer was as follows. The multilayer magnetoresistive film is 1200Å, the permanent magnet layer is 500Å, the insulating layer is 2
00Å, the shield layer is 1 μm.

Further, using the magnetic head having the structure described above, a magnetic recording device having the structure shown in FIG. 7 was manufactured. The magnetic head for reading information is incorporated in the magnetic head 33 together with the inductive write head. After writing on the magnetic recording medium 31 with the write head and reproducing with the magnetic head, a high reproduction output was obtained. This is because the magnetic head of the present invention uses a magnetoresistive element having a high magnetoresistive effect.

In the embodiment, the bias method using a permanent magnet is shown, but the bias method such as shunt bias, soft bias, mutual bias, etc., which is known in the ordinary magnetoresistive head, is also used. The effect of is obtained.

[0031]

According to the present invention, the magnetoresistive change rate is significantly improved as compared with the conventional multilayer film. Further, even if the magnetic field of several tens Oe is applied or not, a change in magnetic resistance of 10% or more can be obtained, so that the information reading performance of the magnetic recording device is dramatically improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a structure of a magnetoresistive effect film of the present invention.

FIG. 2 is a schematic cross-sectional view showing a magnetized state in a multilayer magnetoresistive effect film having discontinuous ferromagnetic layers.

FIG. 3 is a schematic cross-sectional view of a conventional ferromagnetic layer discontinuous multi-layer magnetoresistive effect film.

FIG. 4 is a sectional view showing a method for forming a multilayer film according to an example of the present invention.

FIG. 5 is an example of the present invention (NiFe layer thickness = 2 nm, Ag
FIG. 6 is a characteristic diagram showing the relationship between the magnetoresistance change rate and the number of NiFe layers (layer thickness = 4 nm).

FIG. 6 is a perspective view of a main part of the magnetic head according to the embodiment of the invention.

FIG. 7 is an explanatory diagram of a magnetic recording device according to an embodiment of the invention.

[Explanation of symbols]

 1 ... NiFe layer, 2 ... Ag layer, 3 ... Deposition substrate.

Claims (7)

[Claims] 1. In a magnetoresistive effect film having a structure in which ferromagnetic layers and non-ferromagnetic layers are alternately laminated, the interface on the side far from the substrate as viewed from the non-ferromagnetic layer is closer to the substrate. A magnetoresistive film characterized by being flatter than an interface. 2. The magnetoresistive film according to claim 1, having a structure in which the ferromagnetic layer is divided. 3. The magnetoresistive film according to claim 1, wherein the non-ferromagnetic layer is made of silver. 4. The method for producing a magnetoresistive film according to claim 1, wherein after the non-ferromagnetic layer is deposited, the surface thereof is flattened by sputter etching. 5. The method of manufacturing a magnetoresistive film according to claim 1, wherein the non-ferromagnetic layer is formed by a sputtering method with a negative potential applied to the substrate. 6. A magnetic head using at least a part of the magnetoresistive element according to claim 1, 2, or 3. 7. A magnetic recording device using the magnetic head according to claim 6.