JPH0378682B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a magnetoresistive reproducing head using a current bias method, and more particularly to a magnetoresistive reproducing head in which a bias current is caused to flow through a magnetic shield member. .

[Background of the invention]

In recent years, read heads using magnetoresistive elements, that is, magnetoresistive read heads, have been attracting attention. This utilizes the effect of the magnetoresistive element, in which the electrical resistance value (hereinafter simply referred to as resistance value) changes depending on the strength of the magnetic field, and it is used on tracks formed on the magnetic recording medium. By detecting a magnetic field that changes according to the magnetization pattern of the track as a change in the resistance value of the magnetoresistive element, it is possible to reproduce the information signal recorded on the track.

By the way, spontaneous magnetization (hereinafter simply referred to as magnetization) occurs in the magnetoresistive element, and the direction of this magnetization is as follows when no magnetic field is applied to the magnetoresistive element (hereinafter referred to as a no-magnetic field state).
It is parallel to the easy axis of magnetization of the magnetoresistive element. In this case, when looking at the resistance value in the direction of the easy axis of magnetization, it becomes a large value in such a non-magnetic field state.

Now, when a magnetic field is applied in a direction perpendicular to this easy axis direction, the direction of magnetization in the magnetoresistive element changes to a direction perpendicular to the easy axis depending on the strength of this magnetic field. The resistance value in the easy axis direction becomes smaller as the direction of magnetization approaches the direction perpendicular to the easy axis.

FIG. 1 is a characteristic diagram showing the magnetic field-electrical resistance characteristics of such a magnetoresistive element, in which the horizontal axis represents the strength of the magnetic field in the direction perpendicular to the axis of easy magnetization of the magnetoresistive element.
Furthermore, the resistance value in the easy axis direction is plotted on the vertical axis.

As is clear from the figure, when the magnetic field strength is zero, the magnetoresistive element exhibits the maximum resistance value, and as the magnetic field strength increases, the resistance value decreases regardless of the direction of the magnetic field. . Then, when the strength of the magnetic field exceeds a certain value, the resistance value is saturated and exhibits the minimum resistance value. This resistance value is saturated because the direction of magnetization of the magnetoresistive element is perpendicular to the axis of easy magnetization.

Therefore, a magnetoresistive reproducing head is formed using such a magnetoresistive element, and a track on a magnetic recording medium is formed such that the direction of the magnetic field due to the magnetization pattern is perpendicular to the axis of easy magnetization of the magnetoresistive element. When performing reproduction scanning, the resistance value of the magnetoresistive element changes depending on the strength of the magnetic field due to the magnetization pattern, and since the magnetization pattern above corresponds to the information signal, the resistance value of the magnetoresistive element changes depending on the strength of the magnetic field due to the magnetization pattern. By passing a current in the direction of the axis of easy magnetization, the information signal recorded on the track can be reproduced as a change in current.

The above is the principle of the magnetoresistive read head.

By the way, in the case of reproducing information signals from a magnetic recording medium using such a magnetoresistive reproducing head, when the resistance value of the magnetoresistive element is changed only by the magnetic field caused by the magnetization pattern of the tracks on the magnetic recording medium, represents this magnetic field as H ₁
Then, in FIG. 2, the resistance value changes around point A of the characteristic curve, and a resistance value change of ΔR ₁ is obtained. This resistance value change ΔR ₁ appears as a two-cycle change for one cycle of change in the magnetic field H ₁ .

On the other hand, in FIG. 2, if the resistance value is made to change around the center point B of the straight line portion of the characteristic curve, the resistance value will change for the same change in magnetic field _H1 due to the above magnetization pattern. ΔR ₂ .
This resistance value change ΔR ₂ appears as a one-cycle change in response to a one-cycle change in the magnetic field H ₁ , and the rate of change is larger than when the point A is the operating point.

Therefore, when a current (hereinafter referred to as the detection current) is passed through the magnetoresistive element of the magnetoresistive playback head in parallel to its axis of easy magnetization, the detection current changes due to the above resistance value change. changes, but when point A in Figure 2 is taken as the operating point,
The change in the detection current is small, and this change has a frequency twice that of the information signal recorded on the track, making it impossible to faithfully reproduce this information signal. On the other hand, if point B in Fig. 2 is taken as the operating point, the change in the detection current is very large.
It also faithfully represents the information signals recorded on the track.

For this reason, point B shown in FIG. 2 has conventionally been set as the optimum operating point in magnetoresistive read heads. This optimum operating point B is approximately 0.5H _K to 0.7H _K , where H _K is the anisotropic magnetic field of the magnetoresistive element.
In this case, the direction of magnetization of the magnetoresistive element is inclined at 45° with respect to the axis of easy magnetization. In addition,
Similarly, the center point B' of the linear portion of the characteristic curve in the region where the magnetic field is negative _{in FIG} .

In order to set such an optimal operating point B (or B'), a constant bias magnetic field H _b (second
Figure) must be applied. A conventional and well-known typical method for generating this bias magnetic field is one in which a bias current is passed through a bias conductor and the magnetic field generated by this bias current is used as a bias magnetic field (i.e., current bias method). ). The current bias type magnetoresistive read head further includes one in which a magnetic shield layer provided to block an external magnetic field is used as a bias conductor, and another in which a bias conductor is additionally provided.

Figure 3 shows a conventional multi-track magnetoresistive playback head in which the magnetic shield layer is used as a bias conductor. 1 is a sectional view perpendicular to the moving surface, 1 is a magnetic substrate, 2 is a lower gap, 3 is a magnetoresistive element, 4 is an upper gap,
5 is a magnetic shield layer.

In the same figure a, a lower gap 2 made of a non-magnetic insulating material such as SiO ₂ is formed on a magnetic substrate 1 made of a magnetic material such as Ni-Zn ferrite, and a plurality of tracks with a track width L _t are formed on this lower gap 2. magnetoresistive elements 3 are formed. As this magnetoresistive effect element 3, a permalloy thin film with a film thickness of about 0.05 μm and a width of 2 to 7 μm in the direction perpendicular to the tape sliding surface is used, and generally, as shown in the figure, its easy magnetization axis M is parallel to the tape sliding surface,
Moreover, it is formed so as to be parallel to the track width direction. Further, a conductor (not shown) is connected to the magnetoresistive element 3, and a detection current i _p is passed from this conductor to the magnetoresistive element 3 in a direction parallel to its axis of easy magnetization M.

Further, an upper gap 4 made of SiO ₂ or the like is formed on the lower gap 2 so as to completely cover the magnetoresistive element 3, and a magnetic shield layer 5 is formed on this upper gap 4. The magnetic shield layer 5 is a permalloy thin film with a film thickness of about 2 μm and a width of 30 to 50 μm in the direction perpendicular to the tape sliding surface, and also serves as a bias conductor and carries a constant bias current i _b
is washed away.

The bias current i _b is flowing in the track width direction of the magnetoresistive element 3, and if it is now flowing in the direction shown in FIG. 3b, the bias magnetic field H _b is
It occurs counterclockwise in the drawing with respect to the magnetic shield layer 5, and occurs in the direction of the tape sliding surface in the magnetoresistive element 3. Therefore, this bias magnetic field
Due to H _b , the direction of magnetization of the magnetoresistive element 3 is tilted from the direction parallel to the easy axis M of magnetization (Fig. 3 a) toward the tape sliding surface, and the direction of the magnetization of the magnetoresistive element 3 is tilted in the direction of the easy axis M of magnetization. resistance value decreases. The magnitude of the bias current i _b is set so as to generate a bias magnetic field H _b that brings the operating point of the magnetoresistive element 3 to the optimum operating point B or B' shown in FIG.

As described above, in the conventional magnetoresistive reproducing head described above, a large reproduced output signal can be obtained faithfully and without distortion.

However, in such a conventional magnetoresistive read head, in order to set the operating point of the magnetoresistive element 3 to the optimum operating point B or B', a very large current of 150 to 250 mA is required as the bias current i _b . Therefore, the magnetic shield layer 5 generates heat and the magnetoresistive read head itself is heated. This heating causes thermal noise in the magnetoresistive element 3, etc., and as a result, the S/N of the reproduced signal deteriorates.

This is due to the diamagnetic property of the magnetic shield layer 5, and the diamagnetic field generated in the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface partially cancels out the bias magnetic field H _b caused by the bias current i _b . This is due to a number of reasons. As a result of systematic research on current bias type magnetoresistive read heads such as those of the present invention, it has been found that the bias current i _b necessary for biasing to the optimum operating point B or B' is It was found that it is closely related to the magnetic field coefficient).

FIG. 4 is a graph showing the relationship between the demagnetizing field coefficient in the direction perpendicular to the tape sliding surface of the magnetic shield layer and the bias current density for setting the magnetoresistive element to the optimum operating point, with the horizontal axis The above demagnetizing field coefficient
k _b , and the bias current density i _bp is plotted on the vertical axis.

As is clear from the figure, the larger the demagnetizing field coefficient (therefore, the demagnetizing field) of the magnetic shield layer 5, the larger the bias current density i _bp for setting the magnetoresistive element to the optimum operating point. It can be seen that there is a tendency.

By the way, in general, the demagnetizing field coefficient of a strip-shaped thin film sample is approximately given by t/w, where w is the width of this sample and t is the film thickness. Therefore, in FIGS. 3a and 3b, by increasing the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface, the demagnetizing field coefficient of the magnetic shield layer 5 can be reduced, and the magnetoresistive Bias current density of the magnetic shield layer 5 for setting the effect element 3 to the optimum operating point
i _bp can be decreased.

However, on the other hand, by increasing the width of the magnetic shield layer 5 in the tape sliding surface direction,
Its cross-sectional area increases and eventually the bias current density
This means that the bias current i _b , which is the product of i _bp and this cross-sectional area, has hardly decreased.

As described above, in the conventional magnetoresistive read head, the bias current has to be increased, which has the disadvantage that the S/N ratio of the read signal deteriorates.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetoresistive playback head that eliminates the drawbacks of the prior art described above, requires a small bias current for setting the optimum operating point, and is capable of obtaining a playback signal with a good S/N ratio. There is something to do.

[Summary of the invention]

In order to achieve this object, the present invention comprises a magnetic shielding member consisting of a high permeability magnetic layer and a conductor,
The specific resistance of the conductor is made sufficiently smaller than the specific resistance of the high permeability magnetic layer so that a bias current flows intensively through the conductor, and the demagnetizing field coefficient of the magnetic shielding member is equivalently reduced. It is distinctive in that it did so.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 is a sectional view showing an embodiment of the magnetoresistive read head according to the present invention, in which 6 is a conductor;
7 is a high permeability magnetic layer, and parts corresponding to those in FIG. 3a and b are given the same reference numerals.

In FIG. 5, the magnetic substrate 1 is made of Ni with high magnetic permeability.
The lower gap 2 is made of a -Zn ferrite sintered body, the surface of which is mechanochemically polished to form a film thickness (therefore, gap length) of 0.3 μm made of SiO ₂ or the like. A magnetoresistive element 3 made of 81% Ni permalloy with a thickness of 500 Å is formed on the lower gap 2, and a 0.3 μm thick film made of SiO ₂ or the like is further formed to cover this magnetoresistive element 3. Therefore, an upper gap 4 with a gap length of 0.3 μm is formed.

A magnetic shield layer 5 is formed on the upper gap 4. This magnetic shielding layer 5 consists of a conductor 6 made of Al with a thickness of 2 μm and a high permeability magnetic layer 7 made of Mo permalloy with a thickness of 2 μm in which the conductor 6 is embedded.

The lower gap 2 and the upper gap 4 are formed by RF sputtering, the magnetoresistive element 3 and conductor 6 are formed by vacuum evaporation, and the high permeability magnetic layer 7 is formed by DC facing sputtering. Furthermore, each part can be patterned into a desired shape using a normal photoetching method.

Now, in this embodiment, the specific resistance of the conductor 6 in the magnetic shield layer 5 is
When a bias current is caused to flow through the magnetic shield layer 5, the bias current flows in a concentrated manner through the conductor 6. Therefore, most of the bias magnetic field caused by the bias current flowing through the magnetic shield layer 5 is generated by the current flowing through the conductor 6.

On the other hand, the demagnetizing field coefficient of the conductor 6 is sufficiently smaller than that of the high permeability magnetic layer 7, so that the same amount of current flows through the high permeability magnetic layer 7 due to the current flowing through the conductor 6. A stronger magnetic field is generated than if the The sum of this magnetic field and the magnetic field caused by the slight current flowing through the high permeability magnetic layer 7 becomes the bias magnetic field H _b , but since the strength of this magnetic field is sufficiently large as described above, the high permeability magnetic layer 7 The influence of the demagnetizing field on this bias field is small. Therefore, the demagnetizing field coefficient of the magnetic shield layer 5 becomes equivalently small.

In this case, the cross-sectional area of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface can be made comparable to that of a conventional magnetoresistive playback head, and the demagnetizing field coefficient can be increased without increasing this cross-sectional area. can be reduced. Therefore, the bias current density for setting the magnetoresistive element 3 to the optimum operating point can be reduced, and as a result, the bias current can be reduced.

According to this embodiment, the bias current is reduced by half compared to the above-mentioned conventional technology, and the S/N of the reproduced signal is 3 to 3.
It was improved by about 5dB.

Although numerical values, materials, manufacturing methods, etc. are specifically shown in the above embodiments, the present invention is not particularly limited thereto, and is not limited to multi-track applications. In addition, as for the conductor 6, its specific resistance is 1/1/1 of the specific resistance of the high permeability magnetic layer 7.
Use 10 or less materials.

Furthermore, in the above embodiment, the magnetic substrate 1 has a function as a substrate, but together with the magnetic shield layer 5, it also has a shielding effect against external magnetic fields. However, the present invention is not limited to such a configuration, and particularly in the case of multi-track use, a separate substrate is provided, a high permeability magnetic layer is provided for each magnetoresistive element on the substrate, and a magnetic layer is provided on the substrate for each magnetoresistive element. Each magnetoresistive element may be magnetically shielded by a shield layer.

〔Effect of the invention〕

As explained above, according to the present invention, the demagnetizing field coefficient of the magnetic shield layer can be reduced without increasing the cross-sectional area in the direction perpendicular to the tape sliding surface. The bias current flowing to the
Therefore, the generation of thermal noise can be suppressed, and the S/N ratio of the reproduced signal can be greatly improved, thereby making it possible to provide a magnetoresistive reproduction head with excellent functions without the drawbacks of the above-mentioned conventional technology. .

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the resistance value of the magnetoresistive element with respect to the strength of the magnetic field, Fig. 2 is an explanatory diagram showing the action of the current bias type magnetoresistive playback head, and Fig. 3 a and b are the conventional A front view and a cross-sectional view showing an example of a magnetoresistive read head, and FIG. 4 shows the demagnetizing field coefficient of the magnetic shield layer shown in FIGS. 3a and b and the bias current for setting the magnetoresistive element to the optimum operating point. FIG. 5 is a graph showing the relationship with density, and a sectional view showing an embodiment of the magnetoresistive read head according to the present invention. 1...Magnetic substrate, 2...Lower gap, 3...
Magnetoresistive element, 4... Upper gap, 5...
Magnetic shield layer, 6...conductor layer, 7...high permeability magnetic layer.

Claims (1)

[Claims] 1. A magnetoresistive element in which a predetermined bias current is caused to flow through the first magnetic shield layer in order to set the magnetoresistive element provided between the first high permeability magnetic layer and the magnetic shield layer to an optimum operating point. In the effective type reproducing head, the magnetic shield layer is composed of a second high permeability magnetic layer and a conductive layer, and the resistivity of the conductive layer is 1/10 or less of the resistivity of the second high permeability magnetic layer. A magnetoresistive playback head characterized by: