Spin valve effect magnetoresistive sensor and magnetic head with the sensor

A spin valve effect MR sensor includes a spin valve effect multi-layered structure. This structure has a first thin film layer of ferromagnetic material with one and the other surfaces, a second thin film layer of ferromagnetic material with one and the other surfaces, a thin film spacer layer of nonmagnetic conductive material deposited between the one surfaces of the first and second ferromagnetic material layers, a thin film layer of anti-ferromagnetic material deposited on the other surface of the second ferromagnetic material layer, for pinning the second ferromagnetic material layer, a thin film layer of anti-diffusion material deposited on the other surface of the first ferromagnetic material layer, and a thin film current bypass layer of nonmagnetic conductive material deposited on the thin film anti-diffusion material layer.

FIELD OF THE INVENTION 
The present invention relates to a magnetoresistive (MR) sensor utilizing 
the spin valve effect and a magnetic head with the MR sensor. 
DESCRIPTION OF THE RELATED ART 
A spin valve effect element is known as one of elements providing the giant 
MR effect. This spin valve effect element has a sandwiched structure with 
two ferromagnetic material thin film layers magnetically separated by a 
nonmagnetic metallic spacer thin film layer. An anti-ferromagnetic 
material thin film layer is laminated in contact with one of the two 
uncoupled ferromagnetic material layers so as to produce an exchange 
biasing magnetic field at their boundary and to apply it to this 
ferromagnetic material layer. Therefore, this one ferromagnetic material 
layer (pinned layer) receives the exchange biasing magnetic field, whereas 
the other ferromagnetic material layer (free layer) receives no exchange 
biasing magnetic field so that magnetization switching is introduced by 
different magnetic field between the two ferromagnetic material layers. 
The magnetization directions of the two ferromagnetic material layers 
therefore change between in parallel and in antiparallel with each other 
so that the electrical resistivity of this spin valve effect element 
greatly varies to obtain the large MR effects. 
It has been reported for example in Ching Tsang et al., "Design, 
fabrication & testing of spin-valve read heads for high density 
recording", IEEE transaction magazine, volume 30 No. 6, pp3801-3806, 
November 1994, that amplitude asymmetry of negative and positive signal 
responses of the MR head with the above-mentioned spin valve effect 
element will increase when the sense current supplied to the MR head 
varies. 
When the amplitude asymmetry of negative and positive responses of the 
signal reproduced by the MR head increases, error in amplitude of the 
reproduced signal will increase. Therefore, in case that an amplitude 
detection system is used for processing this reproduced signal, the signal 
error rate will become worse. In case that a peak detection system is used 
instead of the amplitude detection system, influence of noise will 
increase due to smaller differential value at a saturated side of the peak 
than the other side causing also the error rate of the reproduced signal 
to become worse. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a spin valve 
effect MR sensor and a magnetic head with the MR sensor, whereby variation 
of amplitude asymmetry of negative and positive responses of a signal 
reproduced by the MR sensor based upon variation of the sense current can 
be prevented. 
It is another object of the present invention to provide a spin valve 
effect MR sensor and a magnetic head with the MR sensor, whereby a 
characteristics of a free layer in the MR sensor can be prevented from 
deterioration. 
Inventors of this application had studied to prevent the error rate of the 
reproduced signal from becoming worse due to variation of amplitude 
asymmetry of negative and positive responses of a signal reproduced by the 
MR sensor, and had found that the asymmetry variation occurs because the 
center of the sense current flow is positioned at a nonmagnetic metallic 
spacer layer which is sandwiched by the free layer and the pinned layer. 
Namely, since the sense current flows through the MR sensor with keeping 
its center at the nonmagnetic metallic spacer layer, intensity of the 
magnetic field produced by the sense current and applied to the free layer 
varies with the variation of the sense current causing the asymmetry of 
the reproduced signal to greatly change. 
The inventors had therefore considered that if the center of the sense 
current flow is positioned in the free layer, the variation of the 
asymmetry of the reproduced signal with the variation of the sense current 
may be prevented, and thus made the spin valve effect structure with a 
current bypass layer of low resistance metallic material such as Cu, Au or 
Ag formed on a surface of the free layer, which surface is the opposite 
surface against the nonmagnetic metallic spacer layer. By making the 
current bypass layer at this position, the center of the sense current 
flow positions in the free layer or near the free layer causing the 
asymmetry variation due to the sense current magnetic field to reduce. 
However, the current bypass layer made of nonmagnetic metallic material 
such as Cu, Au or Ag directly in contact with the free layer would invite 
diffusion in the free layer during a heating process causing a coercive 
force of the free layer to increase and also its sensitivity to 
deteriorate. 
U.S. Pat. No. 5,422,571 discloses a spin valve effect structure with a 
nonmagnetic electrically conductive material back layer adjacent to the 
free layer for transmitting there through conduction electrons which have 
spins parallel to the direction of magnetization in the free layer so as 
to obtain a larger conductance change. In the specification of this U.S. 
Pat. No. 5,422,579, a multi-layered structure of Ta(50 
Angstroms)/Cu/NiFe(15 Angstroms)/Cu(23 Angstroms)/NiFe(50 
Angstroms)/FeMn(110 Angstroms)/Ta(50 Angstroms) or Ta(50 
Angstroms)/NiFe(20 Angstroms)/FeMn(80 Angstroms)/NiFe(50 Angstroms)/Cu(23 
Angstroms)/NiFe(20 Angstroms)/Ta(30 Angstroms) formed on a substrate is 
disclosed. However, there is no teaching in the U.S. Pat. No. 5,422,579 
with respect to control of position of sense current flow for improving 
variation of the reproduced signal asymmetry. 
According to the present invention, a spin valve effect MR sensor and a 
magnetic head including a transducer element for reading magnetic 
information, constituted by the spin valve effect MR sensor are provided. 
The sensor includes a spin valve effect multi-layered structure having a 
first thin film layer of ferromagnetic material with one and the other 
surfaces, a second thin film layer of ferromagnetic material with one and 
the other surfaces, a thin film spacer layer of nonmagnetic conductive 
material deposited between the one surfaces of the first and second 
ferromagnetic material layers, a thin film layer of anti-ferromagnetic 
material deposited on the other surface of the second ferromagnetic 
material layer, for pinning the second ferromagnetic material layer, a 
thin film layer of anti-diffusion material deposited on the other surface 
of the first ferromagnetic material layer, and a thin film current bypass 
layer of nonmagnetic conductive material deposited on the thin film 
anti-diffusion material layer. 
The spin valve effect multi-layered structure has the first and second 
ferromagnetic layers (pinned layer and free layer) magnetically separated 
by the nonmagnetic spacer layer and the antiferromagnetic layer deposited 
on the pinned layer. When the external magnetic field is not applied, the 
magnetization direction of the free layer is substantially perpendicular 
to the magnetization direction of the pinned layer. The magnetization 
direction of the pinned layer is constrained and held (pinned) by the 
exchange coupling provided by means of the anti-ferromagnetic layer which 
physically contacts with this pinned layer. Contrary to this, the 
magnetization direction of the free layer spins freely depending upon the 
applied external magnetic field. When the sense current is supplied from 
the current source to the MR sensor with such spin valve effect 
multi-layered structure, the voltage drop which is proportional to the 
electrical resistivity variation of the MR sensor caused by the 
magnetization spin in the free layer as a function of the applied external 
magnetic field is appeared across the output terminals of the MR sensor. 
The extent of the electrical resistivity variation of the MR sensor is 
represented by a cosine function of the change in the angle between the 
magnetization directions of the free and pinned layers, which corresponds 
to the magnetic field of data bits recorded on the magnetic medium above 
which this MR sensor runes. 
Particularly, according to the present invention, the structure 
additionally has the current bypass layer deposited on the back of the 
free layer and the anti-diffusion layer deposited between the free layer 
and the current bypass layer. Therefore, variation of amplitude asymmetry 
of negative and positive responses of the signal reproduced by the MR 
sensor based upon variation of sense current can be prevented, and thus 
the error rate of the reproduced signal can be prevented from increasing. 
Also, since the anti-diffusion layer is deposited between the free layer 
and the current bypass layer, the characteristics of the free layer in the 
MR sensor never deteriorate during the heating process. 
It is preferred that the thin film current bypass layer is made of material 
selected from the group consisting of Cu, Ag, Au, a compound containing 
Cu, a compound containing Ag, and a compound containing Au. 
It is also preferred that the thin film current bypass layer has a 
thickness of 8 to 70 Angstroms. 
It is preferred that the anti-diffusion material layer is made or material 
selected from the group consisting of Ta, Ti, Cr, W, Si, Ru, Rh, Pd, Pt, 
Zr, Hf, Nb, Mo, V, and a nonmagnetic compound containing one of Ta, Ti, 
Cr, W, Si, Ru, Rh, Pd, Pt, Zr, Hf, Nb, Mo and V. 
Preferably, the anti-diffusion material layer may be made of an oxide. In 
this case, the oxide may be Al.sub.2 O.sub.3 or SiO.sub.2. 
Preferably, the anti-diffusion material layer is made of a nitride. In this 
case, the nitride may be SiN or AlN. 
Preferably, the anti-diffusion material layer is made of a carbide. In this 
case, the carbide may be SiC or TiC. 
It is also preferred that the anti-diffusion material layer has a thickness 
equal to or more than 3 Angstroms. 
Further objects and advantages of the present invention will be apparent 
from the following description of the preferred embodiments of the 
invention as illustrated in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 which schematically illustrates a spin valve effect MR sensor in 
a preferred embodiment according to the present invention, reference 
numeral 1 denotes a substrate made of for example Al.sub.2 O.sub.3 -TiC. 
On the substrate 1, an under film 2 made of for example Al.sub.2 O.sub.3 
is deposited. On the under film 2, a lower shield layer 3 and a lower 
insulating material layer 4 made of for example Al.sub.2 O.sub.3 are 
sequentially deposited. On the lower insulating material layer 4, a spin 
valve effect multi-layered structure 5 which constitutes a principal 
portion of the MR head is formed. This spin valve effect multi-layered 
structure 5 has side faces in a curved or straight tapered configuration, 
and is formed within the central active region substantially corresponding 
to a track width of the MR head. 
Thin film layers of hard ferromagnetic material 6 and 7 are deposited on 
the lower insulating material layer 4 in contact with the curved or 
straight tapered side faces of the spin valve effect multi-layered 
structure 5. The layers or hard ferromagnetic material 6 and 7 have high 
coercivety and high squareness and are adopted to produce a longitudinal 
bias for maintaining the free layer of the spin valve effect multi-layered 
structure 5 in a single domain state. On the thin film layers of hard 
ferromagnetic material 6 and 7, electrical leads of conductive material 8 
and 9 for transmitting the sense current to the MR sensor and for picking 
up its detected output are deposited in contact with the hard 
ferromagnetic material layers 6 and 7 along the tapered side faces of the 
spin valve effect multi-layered structure 5. 
On the electrical leads 8 and 9 and also on the spin valve effect 
multi-layered structure 5, an upper insulating material layer 10 made of 
for example Al.sub.2 O.sub.3 and an upper shield layer 11 are sequentially 
deposited. A current source 12 for supplying the sense current to the MR 
sensor and also a detection circuit 13 For detecting electrical resistance 
variation of the MR sensor by means of voltage variation are electrically 
connected to the electrical leads 8 and 9. 
In FIG. 2 which illustrates an example of a multi-layered structure of the 
spin valve effect element 5 shown in FIG. 1, reference numeral 20 
indicates a substrate body consisting of the aforementioned substrate 1, 
the under layer 2, the lower shield layer 3 and the lower insulating 
material layer 4, and 21 indicates a buffer layer made of for example Ta 
with thickness of about 50 Angstroms and deposited on the substrate body 
20. On the buffer layer 21, a current bypass layer 22 made of nonmagnetic 
conductive material such as for example Cu with a thickness of about 30 
Angstroms is deposited. This current bypass layer 22 may be made of 
another nonmagnetic conductive material such as Ag, Au, a compound 
containing Cu (for example Cu alloy), a compound containing Ag (for 
example Ag alloy) or a compound containing Au (for example Au alloy), with 
a thickness of about 8-70 Angstroms. 
An anti-diffusion layer 23 made of for example Ta with a thickness of about 
10 Angstroms is deposited on the current bypass layer 22. This 
anti-diffusion layer 23 may be made of another nonmagnetic material such 
as Ti, Cr, W, Si, Ru, Rh, Pd, Pt, Zr, Hf, Nb, Mo, V, or a nonmagnetic 
compound containing any one of Ta, Ti, Cr, W, Si, Ru, Rh, Pd, Pt, Zr, Hf, 
Nb, Mo and V (for example a nonmagnetic alloy containing any one of Ta, 
Ti, Cr, W, Si, Ru, Rh, Pd, Pt, Zr, Hf, Nb, Mo and V). The anti-diffusion 
layer 23 can be made of an oxide such as Al.sub.2 O.sub.3 or SiO.sub.2, a 
nitride such as SiN or AIN, or a carbide such as SiC or TiC. This 
anti-diffusion layer 23 has a thickness of 3 Angstroms or more, preferably 
about 3-20 Angstroms. 
On the anti-diffusion layer 23, a first thin film layer of ferromagnetic 
material (free layer) 24 such as NiFe with a thickness of about 50 
Angstroms, a thin film layer of nonmagnetic conductive material spacer 
layer 25 such as Cu with a thickness of about 25 Angstroms, a second thin 
film layer of ferromagnetic material (pinned layer) 26 such as Cu with a 
thickness of about 25 Angstroms and a thin film layer of 
anti-ferromagnetic material (exchange biasing magnetic material) 27 such 
as FeMn with a thickness of about 100 Angstroms are sequentially deposited 
in this order. The thin film layer 27 provides the anti-ferromagnetic 
exchange coupling to pin the direction of magnetization of the second thin 
film layer 26. 
On the anti-ferromagnetic material thin film layer 27, a capping or 
protection layer 28 made of for example Ta with a thickness of about 50 
Angstroms. 
In other words, the spin valve effect multi-layered structure shown in FIG. 
2 has a layer configuration of Ta(50 Angstroms)/Cu(30 Angstroms)/Ta(10 
Angstroms)/NiFe(50 Angstroms)/Cu(25 Angstroms)/Co(25 Angstroms)/FeMn(100 
Angstroms)/Ta(50 Angstroms) formed on the substrate body 20. 
Since the current bypass layer 22 is formed near the free layer 24, the 
sense current will flow through the spin valve effect structure with 
keeping its center in or near the free layer 24 so as to reduce the 
variation of the asymmetry based upon the sense current magnetic field. As 
a result, the variation of amplitude asymmetry of negative and positive 
responses of the signal reproduced by the MR sensor based upon the 
variation of the sense current can be prevented, and also the error rate 
of the reproduced signal can be prevented from becoming worse. 
In addition, since the anti-diffusion layer 23 is inserted between the 
current bypass layer 22 and the free layer 24 so that the current bypass 
layer 22 does not directly contact with the free layer 24, no diffusion 
will occur during a heating process and thus characteristics of the free 
layer 24, such as its coercive force and its sensitivity, can be prevented 
from deterioration. 
FIG. 3 illustrates asymmetry characteristics of reproduced signals with 
respect to the sense current according to the MR sensor of this embodiment 
and to the conventional MR sensor. The asymmetry of this figure indicates 
a ratio of the difference between the absolute positive peak value and the 
absolute negative peak value of the reproduced signal with respect to the 
sum of both the absolute positive peak and negative peak values. 
According to the conventional spin valve effect structure with no current 
bypass layer, shown as sample 1 in this figure, the asymmetry varies from 
-10% to +20% in response to the variation of the sense current Is from 1 
mA to 6 mA. Whereas according to the embodiment shown as sample 3 which 
has the current bypass layer 22 and the anti-diffusion layer 23 and also 
to the similar layer configuration shown as sample 2, the asymmetry 
variation in response to the variation of the sense current is very small. 
FIG. 4 schematically illustrates a spin valve effect MR sensor in a 
modified embodiment according to the present invention. In this 
embodiment, the spin valve effect multi-layered structure is formed by 
depositing the layers in an order opposite to the above-mentioned order. 
In the figure, reference numeral 40 indicates a substrate body consisting 
of the aforementioned substrate 1, the under layer 2, the lower shield 
layer 3 and the lower insulating material layer 4, arid 47 indicates a 
thin film layer of anti-ferromagnetic material (exchange biasing magnetic 
material) such as for example NiMn with a thickness of about 250 Angstroms 
deposited on the substrate body 40. The thin film layer 47 provides the 
anti-ferromagnetic exchange coupling to pin the direction of magnetization 
of a second thin film layer 46 to be deposited thereon. 
On the anti-ferromagnetic material thin film layer 47, the second thin film 
layer of ferromagnetic material (pinned layer) 46 such as Co with a 
thickness of about 25 Angstroms, a thin film layer of nonmagnetic 
conductive material spacer layer 45 such as Cu with a thickness of about 
25 Angstroms and a first thin film layer of ferromagnetic material (free 
layer) 44 such as NiFe with a thickness of about 50 Angstroms are 
sequentially deposited in this order. 
An anti-diffusion layer 43 made of for example Ta with a thickness of about 
10 Angstroms is deposited on the free layer 44. This anti-diffusion layer 
43 may be made of another nonmagnetic material such as Ti, Cr, W, Si, Ru, 
Rh, Pd, Pt, Zr, Hf, Nb, Mo, V, or a nonmagnetic compound containing any 
one or Ta, Ti, Cr, W, Si, Ru, Rh, Pd, Pt, Zr, Hf, Nb, Mo and V (for 
example a nonmagnetic alloy containing any one of Ta, Ti, Cr, W, Si, Ru, 
Rh, Pd, Pt, Zr, Hf, Nb, Mo and V). The anti-diffusion layer 43 can be made 
of an oxide such as Al.sub.2 O.sub.3 or SiO.sub.2, a nitride such as SiN 
or AlN, or a carbide such as SiC or TiC. This anti-difrusion layer 43 has 
a thickness of 3 Angstroms or more, preferably about 3-20 Angstroms. 
On the anti-diffusion layer 43, a current bypass layer 42 made of 
nonmagnetic conductive material such as for example Cu with a thickness of 
about 30 Angstroms is deposited. This current bypass layer 42 may be made 
of another nonmagnetic conductive material such as Ag, Au, a compound 
containing Cu (for example Cu alloy), a compound containing Ag (for 
example Ag alloy) or a compound containing Au (for example Au alloy), with 
a thickness of about 8-70 Angstroms. 
On the current bypass layer 42, a capping or protection layer 48 made of 
for example Ta with a thickness of about 50 Angstroms. 
In other words, the spin valve effect multi-layered structure shown in FIG. 
4 has a layer configuration of NiMn(250 Angstroms)/Co(25 
Angstroms)/Angstroms)/Cu(25 Angstroms)/NiFe(50 Angstroms)/Ta(10 
Angstroms)/Cu(30 Angstroms)/Ta(5 Angstroms) formed on the substrate body 
40. 
Since the current bypass layer 42 is formed near the free layer 44, the 
sense current will flow through the spin valve effect structure with 
keeping its center in or near the free layer 44 so as to reduce the 
variation of the asymmetry based upon the sense current magnetic field. As 
a result, the variation of amplitude asymmetry of negative and positive 
responses of the signal reproduced by the MR sensor based upon the 
variation of the sense current can be prevented, and also the error rate 
of the reproduced signal can be prevented from becoming worse. 
In addition, since the anti-diffusion layer 43 is inserted between the 
current bypass layer 42 and the free layer 44 so that the current bypass 
layer 42 does not directly contact with the free layer 44, no diffusion 
will occur during a heating process and thus characteristics of the free 
layer 44, such as its coercive and its sensitivity, can be prevented from 
deterioration. 
Table 1 and 2 show asymmetry variation of samples having various layer 
configurations when the sense current changes from 1 mA to 6 mA. 
TABLE 1 
__________________________________________________________________________ 
ASYMMETRY 
VARIATION 
WHEN SENSE 
LAYER CONFIGURATION CURRENT CHANGES 
SAMPLES 
(THICKNESS IS INDICATED BY ANGSTROM) 
1-6 mA 
__________________________________________________________________________ 
S-1 Ta / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 30% 
50 70 25 25 100 50 
S-2 Ta / 
Cu / 
Ta / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 19% 
50 10 3 50 25 25 100 50 
S-3 Ta / 
Au / 
Gr / 
NiFe / 
Co / 
Cu / 
Co / 
FeMn / 
Ta 5% 
50 40 5 40 5 30 20 100 50 
S-4 Ta / 
Ag / 
Ti / 
NiFe / 
CoFe / 
Cu / 
CoFe / 
IrMn / 
Ta 3% 
50 50 15 20 50 25 20 100 50 
S-5 NiMn / 
Co / 
Cu / 
Co / 
NiFe / 
SiN / 
Cu / 
Ta 17% 
250 25 25 5 40 3 20 50 
S-6 Ta / 
NiFe / 
FeMn / 
Co / 
Cu / 
NiFe / 
W / Cu / 
Ta 20% 
50 100 100 20 25 70 20 10 50 
S-7 Ta / 
Au / 
Al.sub.2 O.sub.3 / 
NiFe / 
Cu / 
CoFe / 
PdMn / 
Ta 5% 
50 50 10 70 35 25 100 50 
S-8 Ta / 
Cu / 
Si / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 19% 
50 10 10 50 25 25 100 50 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
ASYMMETRY 
VARIATION 
WHEN SENSE 
LAYER CONFIGURATION CURRENT CHANGES 
SAMPLES 
(THICKNESS IS INDICATED BY ANGSTROM) 
1-6 mA 
__________________________________________________________________________ 
S-9 Ta / 
AuSi / 
Ta / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 3 50 25 25 100 50 
S-10 Ta / 
CuMg / 
TaSi / 
NiFe / 
Cu / 
Cn / 
FeMn / 
Ta 4% 
50 50 10 50 25 25 100 50 
S-11 Ta / 
CuAu / 
AlSi / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 15 50 25 25 100 50 
S-12 Ta / 
AgAl / 
CrPt / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 2% 
50 50 5 50 25 25 100 50 
S-13 Ta / 
AuAg / 
MoSi / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 4% 
50 50 20 50 25 25 100 50 
S-14 Ta / 
AuPt / 
NbTi / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 20 50 25 25 100 50 
S-15 Ta / 
Cu / 
Hf / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 10 50 25 25 100 50 
S-16 Ta / 
Cu / 
RhTa / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 15 50 25 25 100 50 
S-17 Ta / 
Cu / 
RuTa / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 2% 
50 50 15 50 25 25 100 50 
S-18 Ta / 
Cu / 
TiV / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 20 50 25 25 100 50 
S-19 Ta / 
Cu / 
TiZr / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 4% 
50 50 15 50 25 25 100 50 
S-20 Ta / 
Cu / 
MoPt / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 10 50 25 25 100 50 
S-21 Ta / 
Cu / 
SiO.sub.2 / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 10 50 25 25 100 50 
S-22 Ta / 
Cu / 
A1N / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 10 50 25 25 100 50 
S-23 Ta / 
Cu / 
TiC / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 4% 
50 50 10 50 25 25 100 50 
S-24 Ta / 
Cu / 
SiC / 
NiFe / 
Cu / 
Co / 
FeMn / 
Ta 3% 
50 50 10 50 25 25 100 50 
__________________________________________________________________________ 
The sample S-1 has the conventional layer configuration with no current 
bypass layer and therefore provides a large asymmetry variation of 30%. 
The samples S-2 to S-24 are spin valve effect multi-layered structures 
according to the present invention. The sample S-2 uses Cu with the 
thickness of 10 Angstroms as the current bypass layer and Ta with the 
thickness of 3 Angstroms as the anti-diffusion layer. The sample S-3 uses 
Au with the thickness of 40 Angstroms as the current bypass layer and Cr 
with the thickness of 5 Angstroms as the anti-diffusion layer. The sample 
S-4 uses Ag with the thickness of 50 Angstroms as the current bypass layer 
and Ti with the thickness of 15 Angstroms as the anti-diffusion layer. The 
sample S-5 has inverse order for layer deposition and uses Cu with the 
thickness of 20 Angstroms as the current bypass layer and SiN with the 
thickness of 3 Angstroms as the anti-diffusion layer. The sample S-6 also 
has inverse order for layer deposition and uses Cu with the thickness of 
10 Angstroms as the current bypass layer and W with the thickness of 20 
Angstroms as the anti-diffusion layer. The sample S-7 uses Au with the 
thickness of 50 Angstroms as the current bypass layer and Al.sub.2 O.sub.3 
with the thickness of 10 Angstroms as the anti-diffusion layer. The sample 
S-8 uses Cu with the thickness of 10 Angstroms as the current bypass layer 
and Si with the thickness of 10 Angstroms as the anti-diffusion layer. The 
sample S-9 uses AuSi with the thickness of 50 Angstroms as the current 
bypass layer and Ta with the thickness of 3 Angstroms as the 
anti-diffusion layer. The sample S-10 uses CuMg with the thickness of 50 
Angstroms as the current bypass layer and TaSi with the thickness of 10 
Angstroms as the anti-diffusion layer. The sample S-11 uses CuAu with the 
thickness of 50 Angstroms as the current bypass layer and AlSi with the 
thickness of 15 Angstroms as the anti-diffusion layer. The sample S-12 
uses AgAl with the thickness of 50 Angstroms as the current bypass layer 
and CrPt with the thickness of 5 Angstroms as the anti-diffusion layer. 
The sample S-13 uses AuAg with the thickness of 50 Angstroms as the 
current bypass layer and MoSi with the thickness of 20 Angstroms as the 
anti-diffusion layer. The sample S-14 uses AuPt with the thickness of 50 
Angstroms as the current bypass layer and NbTi with the thickness of 20 
Angstroms as the anti-diffusion layer. The sample S-15 uses Cu with the 
thickness of 50 Angstroms as the current bypass layer and Hf with the 
thickness of 10 Angstroms as the anti-diffusion layer. The sample S-16 
uses Cu with the thickness of 50 Angstroms as the current bypass layer and 
RhTa with the thickness of 15 Angstroms as the anti-diffusion layer. The 
sample S-17 uses Cu with the thickness of 50 Angstroms as the current 
bypass layer and RuTa with the thickness of 15 Angstroms as the 
anti-diffusion layer. The sample S-18 uses Cu with the thickness of 50 
Angstroms as the current bypass layer and TiV with the thickness of 20 
Angstroms as the anti-diffusion layer. The sample S-19 uses Cu with the 
thickness of 50 Angstroms as the current bypass layer and TiZr with the 
thickness of 15 Angstroms as the anti-diffusion layer. The sample S-20 
uses Cu with the thickness of 50 Angstroms as the current bypass layer and 
MoPt with the thickness of 10 Angstroms as the anti-diffusion layer. The 
sample S-21 uses Cu with the thickness of 50 Angstroms as the current 
bypass layer and SiO.sub.2 with the thickness of 10 Angstroms as the 
anti-diffusion layer. The sample S-22 uses Cu with the thickness of 50 
Angstroms as the current bypass layer and AlN with the thickness of 10 
Angstroms as the anti-diffusion layer. The sample S-23 uses Cu with the 
thickness of 50 Angstroms as the current bypass layer and TiC with the 
thickness of 10 Angstroms as the anti-diffusion layer. The sample S-24 
uses Cu with the thickness of 50 Angstroms as the current bypass layer and 
SiC with the thickness of 10 Angstroms as the anti-diffusion layer. 
Each of the samples S-2 to S-24 using the current bypass layer and the 
anti-diffusion layer provides very small asymmetry variation with respect 
to the sense current change. 
The thickness of the current bypass layer is preferably 8-70 Angstroms. 
FIG. 5 illustrates asymmetry variation of reproduced signal from a spin 
valve effect multi-layered structure when the sense current changes from 1 
mA to 6 mA (difference between an asymmetry at the sense current of 1 mA 
and an asymmetry at the sense current of 6 mA), with respect to the 
thickness x of the current bypass layer made of Cu. The layer 
configuration of this multi-layered structure is Ta(50 Angstroms)/Cu(x 
Angstroms)/Ta(10 Angstroms)/NiFe(50 Angstroms)/Cu(25 Angstroms)/Co(25 
Angstroms)/FeMn(100 Angstroms)/Ta(50 Angstroms). 
As will be understood from the figure, the asymmetry variation is 40% when 
the thickness of the current bypass layer x is zero (x=0), namely there is 
no current bypass layer whereas the asymmetry variation is very small, 
namely within .+-.25%, when the thickness of the current bypass layer x is 
8 to 70 Angstroms (x=8 to 70). If the asymmetry variation is out of the 
range .+-.25%, the error rate becomes very large and therefore it is 
impossible to use as the MR sensor for a magnetic read head. 
Many widely different embodiments of the present invention may be 
constructed without departing from the spirit and scope of the present 
invention. It should be understood that the present invention is not 
limited to the specific embodiments described in the specification, except 
as defined in the appended claims.