Magnetoresistive magnetic head

In a magnetoresistive magnetic head having a laminate composed of a magnetoresistive (MR) layer showing the magnetoresistive effect, a SHUNT layer as a non-magnetic layer and a soft adjacent layer (SAL) for applying a transverse bias magnetic field to the MR layer, the MR layer and the SAL are made of the same Ni.sub.81 Fe.sub.19 magnetic film. Since the SAL is magnetically saturated in the same direction as the direction of leakage flux of a recording medium (y direction), permeability thereof in the y direction decreases, and the MR effect function therein can be restricted. Although the MR layer and the SAL have the same specific resistance .rho., a sufficient detection current can be made to flow through the MR layer and a high-precision magnetic detection output can be obtained by making the MR layer thicker than the SAL.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic head comprising a laminate of 
thin films, and more particularly, to a magnetoresistive magnetic head 
having a trilayer structure composed of a magnetoresistive (MR) layer, a 
SHUNT layer and a soft adjacent layer (SAL). 
2. Description of the Related Art 
FIGS. 5 and 6 are enlarged front views respectively showing a hard bias 
magnetoresistive magnetic head and an exchange bias magnetoresistive 
magnetic head as viewed from the side opposed to a recording medium. 
These magnetoresistive magnetic heads each have a trilayer structure 
composed of a MR layer 1 showing the magnetoresistance effect, a SHUNT 
layer 2 as a non-magnetic layer, and a SAL 3 for applying an SAL bias 
magnetic field (a transverse bias in the y direction) to the MR layer 1. 
The trilayer structure is provided between a lower insulating layer 4 and 
an upper insulating layer 5. 
In order to apply a longitudinal bias magnetic field in the x direction to 
the MR layer 1 in the hard bias method shown in FIG. 5, hard bias layers 7 
made of hard magnetic material are formed on both sides of the MR layer 1, 
and each sandwiched between a substrate layer 6 and a lead layer 8. The 
hard bias layers 7 are magnetized in the x direction, and applies a 
magnetically anisotropic magnetic field to the MR layer 1, by which the MR 
layer 1 is put into a single domain state. 
In the exchange bias method shown in FIG. 6, an antiferromagnetic layer 9 
is formed on the MR layer 1 in close contact, and a lead layer 10 is 
further formed thereon. Exchange anisotropic coupling of the 
antiferromagnetic layer 9 and the MR layer 1 magnetizes the MR layer 1 in 
the x direction to thereby induce a single domain state. 
Stationary current in the x direction is applied from the lead layer 8 and 
the hard bias layer 7 to the MR layer 1 in FIG. 5, and stationary current 
in the x direction is applied to the MR layer 1 through the lead layer 10 
and the antiferromagnetic layer 9 in FIG. 6. A transverse magnetic field 
is also applied to the MR layer 1 in the y direction by magnetostatic 
coupling energy generated by the SAL 3 when the current flows through the 
MR layer 1. When the MR layer 1 is put into a single domain state in the x 
direction and given the transverse bias magnetic field from the SAL 3, the 
resistance change with the change in the magnetic field of the MR layer 1 
is set in a linear state. 
Conventionally, it is preferable that the MR layer 1 be made of a material 
having a high magnetoresistive effect ratio (MR effect ratio) 
(.DELTA..rho./.rho.) and the SAL 3 be made of a material having a low MR 
effect ratio (.DELTA..rho./.rho.), wherein .rho. represents the specific 
resistance and .DELTA..rho. represents the amount of change in the 
specific resistance relative to the magnetic field. Furthermore, it is 
preferable that the material of the MR layer 1 have a low specific 
resistance .rho. to allow the current to flow smoothly and the material of 
the SAL 3 have a high specific resistance .rho.. Therefore, 
conventionally, the MR layer 1 is made of ferromagnetic material such as a 
Ni--Fe material, and the SAL 3 is made of soft magnetic material such as a 
Co amorphous material, a Ni--Fe--Nb material or a Ni--Fe--Zr material. The 
material of the SHUNT layer 2 is, for example, a Ta film. 
Thus, the MR layer 1, the SHUNT layer 2 and the SAL 3 are conventionally 
made of different materials. Therefore, three kinds of targets 
respectively corresponding to the materials of the three layers are needed 
to form the layers by sputtering. Furthermore, three pairs of electrodes 
are needed in a sputtering apparatus to continuously form the layers in a 
stable thickness. 
SUMMARY OF THE INVENTION 
In view of the foregoing problems with the prior art, it is an object of 
the present invention to provide a magnetoresistive magnetic head in which 
three layers, MR, SHUNT and SAL, can be formed by the minimum number of 
kinds of materials and which can show an excellent magneto-resistive 
effect. 
In order to achieve the above object, there is provided a magnetoresistive 
magnetic head having a trilayer structure composed of a MR layer showing 
the magnetoresistive effect, a SHUNT layer as a non-magnetic layer and a 
SAL for applying a bias magnetic field to the MR layer, wherein the MR 
layer and the SAL are made of the same magnetic material and the thickness 
of the MR layer is larger than that of the SAL. 
The MR layer and the SAL may be both made of a Ni--Fe magnetic material. 
It is preferable that the ratio of the MR layer to the SAL thickness be in 
a range of 0.4 to 0.7. 
According to the present invention, the MR layer and the SAL out of the 
trilayer structure are made of the same magnetic material, for example, 
Ni.sub.81 Fe.sub.19 (atm %). Therefore, the MR layer and the SAL have the 
same MR effect ratio (.DELTA..rho./.rho.). However, the magnetic 
permeability .mu. of the SAL relative to a leakage magnetic field of a 
recording medium can be decreased by saturating magnetization toward the 
leakage magnetic field in the SAL, which allows restraint on the MR effect 
in the SAL and fulfillment of an original function of the SAL. 
Furthermore, since the MR layer and the SAL have the same specific 
resistance .rho., a stationary current (detection current) to be applied 
to the MR layer is liable to be diverted to the SAL. However, a sufficient 
current can be applied to the MR layer and a sufficient change in 
resistance relative to the leakage magnetic field of the recording medium 
can be obtained by choosing the thickness ratio between the MR layer and 
the SAL from a proper range. When the MR layer and the SAL are both made 
of a Ni--Fe magnetic material, a preferable thickness ratio of the MR 
layer to the SAL is in a range Of 0.4 to 0.7.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will be described below. 
A magnetoresistive magnetic head according to an embodiment of the present 
invention is provided with a trilayer device, shown in FIG. 1, composed of 
a MR layer 1 showing the magnetoresistive effect, a SHUNT layer 2 as a 
non-magnetic layer and a soft adjacent layer (SAL) for applying a SAL bias 
magnetic field (transverse magnetic field) to the MR layer 1. The 
thicknesses of the MR layer 1, the SHUNT layer 2 and the SAL 3 are 
respectively represented by t1, t2 and t3, and the depth of all the layers 
in the y direction is represented by D. 
The trilayer device shown in FIG. 1 is suitably used in the hard bias 
magnetoresistive magnetic head shown in FIG. 5. In the hard bias type, the 
trilayer device shown in FIG. 1 is formed on a lower insulating layer 4. 
Hard bias layers 7 of hard magnetic material are formed on both sides of 
the MR layer 1, and each sandwiched between a substrate layer 6 thereunder 
and a lead layer 8 thereon. Furthermore, an upper insulating layer 5 is 
formed on the MR layer 1 and the lead layer 8. The track width in this 
magnetic head is represented by Tw in agreement with the width of the MR 
layer 1. 
In this embodiment, the MR layer 1 and the SAL 3 are formed of the same 
Ni--Fe magnetic material, more specifically, a Ni.sub.81 Fe.sub.19 (atm %) 
magnetic film, and the SHUNT layer 2 is formed of a Ta film. Preferable 
thicknesses t1, t2 and t3 of the MR layer 1, the SHUNT layer 2 and the SAL 
3 are respectively 300 .ANG., 150 .ANG. and 165 .ANG.. A preferable track 
width Tw is 3.5 .mu.m. 
The hard bias layers 7 are made of hard magnetic material such as a 
Co--Cr--Ta material, and the substrate layer 6 and the lead layer 8 are 
formed of a Cr film. 
In this embodiment, the MR layer 1 and the SAL 3 are formed of the same 
Ni.sub.81 Fe.sub.19 magnetic film. The Ni.sub.81 Fe.sub.19 magnetic film 
has a MR effect ratio (.DELTA..rho./.rho.) of approximately 2% to 3%, and 
can show a sufficient magnetoresistive effect as the MR layer 1. Although 
it is conventionally thought that a material having a low MR effect ratio 
is suitable as the material of the SAL, the SAL in this embodiment is made 
of the same material as the MR layer 1, and also has the same MR effect 
ratio (.DELTA..rho./.rho.) as the MR layer 1. 
However, the magnetic permeability .mu. of the SAL 3 in the y direction can 
be decreased by saturating magnetization of the SAL 3 in the y direction 
by magnetostatic coupling when current is applied to the MR layer 1. In 
other words, in the device shown in FIG. 1, the SAL 3 is magnetized in the 
y direction (By) by magnetostatic coupling when a stationary current 
(detection current) in the x direction is applied to the MR layer 1, and 
this magnetization gives a transverse bias magnetic field to the MR layer 
1. In the MR layer 1 which is put in an x-direction single domain state by 
a magnetically anisotropic magnetic field from the hard bias layer 7, the 
magnetization direction (B.theta.) is pointed at an angle of .theta. (for 
example, 45.degree.) relative to the x direction by the transverse 
magnetic field applied from the SAL 3. 
Therefore, although the magnetic permeability .mu. of the MR layer 1 is 
high in the direction of a leakage flux from a recording medium (y 
direction), the magnetic permeability .mu. of the SAL 3 in the y direction 
is decreased and the MR effect function thereof is restricted. 
Accordingly, the SAL 3 can serve a sufficient biasing function even if it 
is made of the same magnetic material as that of the MR layer 1. 
The MR layer 1 and the SAL 3 are made of the same material, and therefore, 
have the same specific resistance .rho.. Therefore, the MR layer 1 and the 
SAL 3 are required to be different in volume to apply a sufficient 
stationary current to the MR layer 1. Since it is general in the magnetic 
head that the MR layer 1 and the SAL 3 have the same dimensions in the x 
and y directions, it is necessary to make a difference in thickness 
between the MR layer 1 and the SAL 3 to make the volumes thereof 
different. The difference in thickness makes a difference in the diversion 
ratio of the stationary currents to be applied to the MR layer 1 and the 
SAL 3, by which a sufficient stationary current can be applied to he MR 
layer 1. In the embodiment shown in FIG. 1, the thickness t1 of the MR 
layer 1 is 300 .ANG., the thickness t3 of the SAL 3 is 165 .ANG., and the 
ratio of the thickness t3 of the SAL 3 to the thickness t1 of the MR layer 
1 (t3/t1) is set at 0.55. 
The hard bias type magnetoresistive magnetic head shown in FIG. 5 was 
produced by using the above-mentioned trilayer device consisting of the MR 
layer 1 of a Ni.sub.81 Fe.sub.19 magnetic film having a thickness t1 of 
300 .ANG., the SAL 3 similarly made of a Ni.sub.81 Fe.sub.19 magnetic film 
having a thickness t3 of 165 .ANG. and the SHUNT layer 2 of a Ta film 
having a thickness t2 of 150 .ANG.. The change curve of the magnetic field 
(M) and the detection voltage (V) at this time is shown in FIG. 2. This 
M-V change curve is proportional to the M(magnetic field)-R(electric 
resistance) change curve. The dimension of the trilayer device in the x 
direction, that is, Tw is 3.5 .mu.m and the depth thereof in the y 
direction is 2.0 .mu.m. 
FIGS. 2(A) to 2(C) show measured values when external magnetic fields 
varying in a range of .+-.100 Oe are applied to the trilayer device in the 
y direction. The stationary currents applied to the trilayer device in the 
x direction in the cases shown in FIGS. 2(A), 2(B) and 2(C) are 
respectively 5 mA, 10 mA and 15 mA. FIG. 2 reveals that a sufficient 
magnetoresistive effect, that is, detection output can be obtained and 
little Barkhausen noise arises when the MR layer 1 and the SAL 3 are made 
of the same Ni.sub.81 Fe.sub.19 magnetic film, the thickness ratio (t3/t1) 
is 0.55, a stationary current of approximately 10 mA or 15 mA is applied 
and the strength of the leakage magnetic field from the recording medium 
is approximately .+-.100 Oe. 
FIG. 3 Shows the relationship between the thickness ratio (t3/t1) between 
the MR layer 1 and the SAL 3 and the change rate in voltage between the 
positive side and the negative side of the detection output when the MR 
layer 1 and the SAL 3 are made of the same Ni.sub.81 Fe.sub.19 magnetic 
film. This is the measurement result when the trilayer device shown in 
FIG. 1 has a dimension in the x direction (Tw:track width) of 3.5 .mu.m 
and a depth D in the y direction of 2.0 .mu.m and is used as a component 
of the hard bias type magnetic head shown in FIG. 5. The change rate of 
the detection output can be found from the following Formula 1 
##EQU1## 
wherein Vp represents the peak value on the positive side of the detection 
voltage and Vn represents the peak value on the negative side when a 
stationary current of 10 mA is applied and leakage magnetic fields varying 
in a range of .+-.100 Oe are applied in the y direction. 
It is known from FIG. 3 that there is little difference between the voltage 
from a point 0 to the peak value (Vp) on the positive side of the 
detection output and the voltage from the point 0 to the peak value (Vn) 
on the negative side and the M-R change has an excellent linearity when 
the ratio of the thickness t3 of the SAL 3 to the thickness t1 of the MR 
layer 1 (t3/t1) is about 0.55. Furthermore, when the thickness ratio 
(t3/t1) is in a range of 0.4 to 0.7, the change rate is in a range of 
-12.5% to +14%. This range is sufficiently practical. In order to set the 
change rate below .+-.10%, the thickness ratio (t3/t1) is required to be 
in a range of 0.43 to 0.66. 
Therefore, a preferable ratio of the thickness t3 of the SAL 3 to the 
thickness t1 of the MR layer 1 (t3/t1) is in a range of 0.4 to 0.7, more 
preferably, a range of 0.43 to 0.66. 
FIG. 4 shows the relationship between the depth D of the trilayer device in 
the y direction shown in FIG. 1, and the peak-to-peak value Vpp of 
reproduction output (in microvolts .mu.V). This is the measurement result 
when the hard bias type magnetic head shown in FIG. 5 is constituted by 
using a device in which the MR layer 1 and the SAL 3 are made of a 
Ni.sub.81 Fe.sub.19 magnetic film, the SHUNT layer 2 is made of a Ta film, 
t1 is 300 .ANG., t2 is 150 .ANG., t3 is 165 .ANG. and Tw is 3.5 .mu.m. 
As the depth D in the y direction of the device shown in FIG. 1 increases, 
the reproduction output decreases. It seems that this is because the 
electric resistance of the SAL 3 decreases as the volume thereof 
increases, the stationary current is liable to be diverted to the SAL 3 
and therefore the reproduction output decreases. The reproduction output 
Vpp is required to be more than 400 .mu.V, and a preferable y-direction 
depth D of the trilayer device is less than 2.3 .mu.m. 
Although the hard bias magnetic head shown in FIG. 5 is constituted by 
using the trilayer device shown in FIG. 1 in the above-described 
embodiment, the MR layer 1 and the SAL 3 may also be made of the same 
magnetic material in the exchange bias magnetic head shown in FIG. 6. In 
this case, a high-precision detection output without any Barkhausen noise 
can be obtained by setting an appropriate volume ratio between the MR 
layer and the SAL, that is, an appropriate thickness ratio therebetween. 
As described above, according to the present invention, since the MR layer 
and the SAL are made of the same magnetic material, they can be formed by 
using the same target in producing a magnetic head by sputtering, and 
production is simplified. A sufficient current applied to the MR layer can 
be secured and a sufficient MR effect can be shown by making the MR layer 
thicker than the SAL and setting the thickness ratio in an appropriate 
range.