Yoke thin film magnetic head constructed to avoid Barkhausen noises

The yoke thin film magnetic head according to the present invention includes yokes for leading the magnetic flux of signals generated from the magnetic recording medium up to the magnetic resistance effect element, which yokes are made of sputtered films having compressive stress therein. Therefore, the internal stress in the yokes which cause bad influences upon magnetic properties of the magnetic resistance effect element can be negated or reduced, with less Barkhausen noises produced.

BACKGROUND OF THE INVENTION 
The present invention relates to a thin-film yoke magnetoresistive head (`a 
yoke thin film magnetic head` is referred to as a YMR head hereinbelow) 
which is provided with a magnetoresistive element (`a magnetic resistance 
effect element` is referred to as an MR element hereinbelow) applying the 
magnetoresistive effect of a ferromagnetic thin film so as to detect the 
magnetic flux of signals recorded onto a magnetic recording medium. 
As shown in FIG. 19, a known YMR head is comprised of a first insulation 
layer 52 formed on a substrate 51 having high permeability, a conductor to 
apply bias magnetic field to an MR element formed on the first insulation 
layer 52, a second insulation layer 53 covering the conductor 54, an MR 
element 55 placed on the second insulation layer 53, a gap insulation 
layer 56 so formed as to cover all of the MR element 55, the second 
insulation layer 53 and the first insulation layer 52, a first yoke 57 and 
a second yoke 58. The YMR head is placed adjacent to a magnetic recording 
medium 59. 
For the yokes 58 and 57 formed on the gap insulation layer 56, sputtered 
Ni-Fe films are employed because of their readiness for property control, 
their superior productivity and magnetic properties enjoyed in the case 
where a step difference is present in the substrate 51, etc. 
In general, however, the sputtered Ni-Fe films referred to above cannot 
display satisfactory magnetic properties unless they are applied with high 
negative substrate bias when sputtered (with reference to I.E.E.E. 
TRANSACTION ON MAGNETIC, VOL. MAG-15, NO. 6 (1979) p. 1821 
"Structure-sensitive Magnetic Properties of RF Sputtered Ni-Fe Films"). In 
other words, if the substrate biasing voltage is low, the direction of the 
easy axis of the sputtered films is vertical to the film surface. 
Moreover, in the case where no negative substrate bias is applied during 
sputtering, it is necessary that the target voltage should be high to 
increase the energy of particles incident on the substrate. Accordingly, a 
residual compressive stress in the sputtered Ni-Fe films increases due to 
the peening effect in any of the aforementioned manners. The residual 
stress in the magnetic thin film constituting the first and second yokes 
57 and 58 remains even after the thin film is processed into the shape of 
a yoke. As a result of reaction to the residual internal stress in the 
yokes 57 and 58, it induces stress in the MR element 55. The induced 
stress in turn gives rise to a magnetic anisotropy within the MR element 
55, which fact disturbs the magnetic anisotropy naturally induced to the 
MR element when the MR element 55 is evaporated. This anisotropy 
dispersion in the MR element 55 results in discontinuities of the 
magnetization curve inside the MR element 55, thereby giving rise to the 
generation of Barkhausen noises. Thus, as described above, the residual 
stress in the yokes has a bad influence on the characteristic of YMR head 
and therefore, it has been strongly desired to hold the internal stress to 
as small an amount as possible. However, since it is difficult to reduce 
the residual compressive stress of the sputtered film itself such as 
sputtered Ni-Fe film, it has been disadvantageous that Barkhausen noises 
are inevitably generated when the sputtered Ni-Fe film is used for the 
yoke material. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention has been developed with a view to 
substantially eliminating the above-described disadvantage, and has for 
its essential object to provide a yoke thin film magnetic head, i.e., a 
YMR head which is arranged to cancel the residual compressive stress in 
the yokes indirectly to thoroughly restrict the generation of Barkhausen 
noises resulting from the internal compressive stress. 
In accomplishing the above-mentioned object, according to one preferred 
embodiment of the present invention, there is provided a yoke thin film 
magnetic head having yokes arranged in such a manner as to conduct the 
magnetic flux of signals generated from a magnetic recording medium to a 
magnetic resistance effect element, which yokes are made of sputtered 
films having the compressive stress therein. The yoke thin film magnetic 
head is further formed with an evaporated metal film having high melting 
points onto the yokes. Since the evaporated metal film of high melting 
points has internal tensile stress approximately equal to the internal 
compressive stress in the yokes, the thin film magnetic head of the 
present invention is effective to indirectly solve the bad influences 
occasioned by the internal compressive stress generated in the yokes upon 
a magnetic resistance effect element. 
Furthermore, the yoke thin film magnetic head of the present invention 
includes the magnetic resistance effect element which detects the magnetic 
field of signals generated in the magnetic recording medium as the change 
in resistance, yokes for leading the magnetic flux from a head gap to the 
MR element, DC magnetic field application members for applying a desired 
weak magnetic field to the MR element in the longitudinal direction of the 
MR element and a conductor for applying a desired biasing magnetic field 
to the MR element in the stripe widthwise direction of the MR element. In 
the yoke thin film magnetic head, the easy magnetization axis of the MR 
element is inclined 5.degree.-20.degree. in the longitudinal direction of 
the MR element, such that the discontinuities are observed either at the 
positive side or at the negative side of the abscissa of .DELTA.R/R curve, 
namely, the magnetic field Ha corresponding to the signal magnetic field. 
Moreover, the operating point of the MR element is moved to a point good 
at linearity, that is, to the side of the magnetic field Ha without the 
discontinuities observed. Accordingly, the magnetization switching takes 
place in the magnetic field area in the same direction as the biasing 
magnetic field can be avoided, and Barkhausen noises generated as a result 
of the magnetization switching can be prevented. 
The thin film magnetic head is covered with a pattern of a yoke film for 
conducting the magnetic flux to the MR element. The pattern of a yoke film 
is coated with a stress cancel so as to cancel or reduce the stress 
generated inside the yoke film. 
Another important object of the present invention is to provide a magnetic 
resistance effect thin film head. The magnetic resistance effect thin film 
head has a first yoke, a magnetic resistance effect element (MR element) 
and a second yoke, each made of ferromagnetic thin film, magnetically 
united with each other sequentially in this order on a substrate. In the 
magnetic resistance effect thin film head, when the internal stress of the 
first and the second yokes is larger than zero, the magnetostriction 
constant of the MR element is set to be smaller than zero. On the other 
hand, when the internal stress of the first and the second yokes is 
smaller than zero, the magnetostriction constant of the MR element is 
determined to be larger than zero. Accordingly, because of this structure, 
although the magnetic anisotropy is caused in the MR element by the 
internal stress generated in the first and the second yokes, the direction 
of the magnetic anisotropy in the MR element is made coincident to the 
direction of the induced magnetic anisotropy naturally inherent in the MR 
element. Accordingly, the dispersion of anisotropy can be avoided, and 
therefore, the generation of Barkhausen noises can be restricted.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
Before the description of the present invention proceeds, it is to be noted 
here that like parts are designated by like reference numerals throughout 
the accompanying drawings. 
Referring to FIGS. 1 to 9, a yoke thin film magnetic head according to a 
first embodiment of the present invention will now be described 
hereinafter. For sake of convenience in description, however, it is to be 
noted that FIGS. 8 and 9 are to be used, with reference numerals in FIGS. 
8 and 9 corresponding to those in FIG. 1. 
FIG. 8 shows the construction of a yoke thin film magnetic head (referred 
to as a YMR head) according to the present invention. The yoke thin film 
magnetic head has upper yokes 1 and 5 made of permalloy film generally 
having the film thickness of about 0.1-4.0 .mu.m and forming an 
introduction path of the magnetic flux for introducing the magnetic field 
of signals produced in a magnetic recording medium to an MR element 2. 
Ferromagnetic films 3 and 3 have excellent conductivity and high coercive 
force, which are made of Co-P, Ni-Co, Ni-Co-P, etc, with the thickness of 
1000-2000 .ANG.. Lead conductors 4 and 4 are made of Al-Cu film of 
1000-10000 .ANG. in thickness. Further, an electric conductor 6 made of 
Al-Cu is provided below the MR element 2 in order to apply the biasing 
magnetic field to the MR element 2. A lower yoke 7 is fabricated by a high 
magnetic permeability material such as polycrystal Ni-Zn ferrite substrate 
or, single crystal or polycrystal Mn-Zn ferrite substrate or, 
ferromagnetic metal. A head gap 10 is set to be approximately 0.1-0.3 
.mu.m since the recording wavelength in actual use is about 0.5 .mu.m at 
the smallest. Moreover, as shown in FIG. 9, a magnetic recording medium 9 
is placed near the head gap 10 and a spacing 8 is formed between the 
magnetic recording medium 9 and the head gap 10. 
Accordingly, the YMR head according to the first embodiment of the present 
invention is, as shown in FIGS. 8 and 9, comprised of the magnetic 
resistance effect element, that is, MR element 2 for detecting the 
magnetic flux of signals generated in the magnetic recording medium 9 as 
the change in resistance, the upper yokes 1 and 5 for leading the magnetic 
flux of signals from the head gap 10 to the MR element 2, the 
ferromagnetic films 3 and 3 working as a DC magnetic field applying 
members for applying a desired weak magnetic field to the MR element in 
the longitudinal direction thereof so as to make the MR element 2 into a 
single magnetized area, and the electric conductor 6 for applying a 
desired biasing magnetic field to the MR element 2 in the strip widthwise 
direction thereof. In the YMR head having the above-described structure, 
the easy axis of the magnetic anisotropy in the MR element 2 is inclined 
at 10.degree. in the clockwise direction with respect to the longitudinal 
direction of the MR element 2, as shown in FIG. 1. 
The ferromagnetic film 3 applies the weak magnetic field to the MR element 
in the direction shown by arrows, namely, from left to right in FIG. 1. 
Moreover, the direction of the easy magnetization axis in the MR element 2 
in each point of the element is angularly dispersed to the same extent 
both at the positive side and at the negative side of the set 
magnetization easy axis. Supposing that the angle dispersion is 
approximately .+-.10.degree., the direction of the easy magnetization axis 
extends in the range of 0.degree.-20.degree. in the longitudinal direction 
of the MR element 2 all over the element 2. For example, at the point a on 
the MR element 2, the easy magnetization axis is inclined at 20.degree. 
with respect to the longitudinal direction of the MR element. On the other 
hand, at the point e of the MR element 2, the easy magnetization axis 
turns approximately the same direction as the longitudinal direction of 
the MR element. Therefore, there is no zone or area in the MR element 2 
where the easy magnetization axis is inclined in the counterclockwise 
direction to the longitudinal direction. At this time, the magnetization 
curve in the stripe widthwise direction of the MR element 2 at points a, 
b, c, d and 3 is represented respectively in FIGS. 2(a) to 2(e), while the 
.DELTA.R/R curve is represented in FIG. 2(f). It is noticed from this FIG. 
2(f) that discontinuities are brought about on a part of the .DELTA.R/R 
curve only at the negative side of the magnetic field Ha. Accordingly, 
when the operating point of the MR element 2 is shifted to a point good at 
linearity by selecting the polarity of the biasing magnetic field, and the 
good point is at the positive side of the magnetic field Ha, the 
generation of Barkhausen noises which would otherwise be produced when the 
YMR head reproduces the magnetic field of signals can be suppressed. It is 
to be noted here that if the easy magnetization axis is inclined at 
10.degree. in the counterclockwise direction to the longitudinal direction 
of the MR element 2 when the element is fabricated, reverse direction to 
that in FIG. 1, with the other conditions maintained the same, 
discontinuities are observed on the .DELTA.R/R curve at the positive side 
of the magnetic field Ha, showing the reverse representation of the curve 
from FIG. 2(f). It this case, the MR element 2 should be applied with such 
biasing magnetic field as to shift the operating point of the MR element 
to the negative side of the magnetic field Ha so that Barkhausen noises 
are never contained in reproduced output signals. 
In the meantime, the main points for deciding the inclination angle of the 
easy magnetization axis with respect to the longitudinal direction of the 
MR element 2 (referred to as an inclination angle in the easy axis 
hereinbelow) when the MR element is fabricated will be described. 
The MR element 2 of the YMR head responds to the magnetic field of signals 
in the condition that the demagnetization field in the MR element is small 
because the MR element is connected magnetically with the upper yokes 1 
and 5, and the lower yoke 7. Further, since the MR element 2 is applied 
with weak magnetic field by the ferromagnetic film 3 which has high 
coercive force, the MR element 2 is in a single magnetic domain state. 
Taking these viewpoints into consideration, a suitable value for the 
anisotropic inclination angle can be estimated from Stoner-Wohlfarth's 
single domain model shown in FIG. 3. In FIG. 3, references .theta.', 
H.sub.E, Ms and Ha represent the anisotropic inclination angle, weak 
magnetic field applied to the MR element 2 by the ferromagnetic film 3, 
saturated magnetization of the MR element 2 and the external magnetic 
field corresponding to the magnetic field of signals, respectively. Now, 
the rotational angle .phi. of the magnetization M in the MR element with 
respect to the external magnetic field Ha is calculated on the basis of 
properties of the MR element fabricated for trial, with supposing that 
H.sub.E is 1.3 [Oe], Ms is 796 [emu/cc] and H.sub.K is 4 [Oe], in such 
manner that the sum of the anisotropy energy and the magneto-static energy 
of the magnetization M is rendered to be minimized. Then, the 
magnetization curve in the x direction (shown in FIG. 3) and the 
.DELTA.R/R curve are obtained, which are shown in FIGS. 4-7(a) and 4-7(b), 
respectively. As shown in FIGS. 6(a) and 6(b), when the anisotropic 
inclination angle .theta. is about 20.degree., the switching of the 
magnetization occurs at the positive side of the external magnetic field 
Ha. Further, as shown in FIGS. 7(a) and 7(b), when the anisotropic 
inclination angle .theta. is 25.degree. or so, not only the switching of 
the magnetization takes place both at the positive side and at the 
negative side of Ha, and the magnetization curve splits into two (referred 
to as a hysteresis hereinbelow). On the other hand, when the same 
calculation is conducted with the other conditions remaining the same as 
in the above case except that H.sub.E is supposed to be 0.8 [Oe], the 
switching of the magnetization is brought about at the positive side of Ha 
when the anisotropic inclination angle .theta. is about 12.degree.. As the 
anisotropic inclination angle .theta. is increased, the switching of the 
magnetization is given rise to both at the positive side and at the 
negative side of Ha. In addition to the above, it is confirmed that a 
hysteresis comes to be brought about in the magnetization curve in 
accordance with the increase of the anisotropic inclination angle .theta.. 
As described above, if the anisotropic inclination angle .theta. exceeds 
some threshold value depending on the magnetic properties of the MR 
element 2 and H.sub.E, the switching of the magnetization is brought about 
at both sides of Ha, causing Barkhausen noises. Meanwhile, it is proven 
that, if the anisotropic inclination angle .theta. is in the range where 
switching of the magnetization occurs at one side of Ha, the sensibility 
of the MR element 2 (indicated by the inclination in the tangential 
direction at each point of the .DELTA.R/R curve) drops in accordance with 
the increase of the anisotropic inclination angle .theta.. Based on the 
result of the foregoing calculations and, considering the magnetic 
properties of a general MR element and the fact that the angle dispersion 
of the easy magnetization axis in the general MR element is approximately 
5.degree.-10.degree., it is proper that the inclination of the easy 
magnetization axis of the MR element 2 should be set to be 
5.degree.-20.degree.. 
Accordingly, because of the above arrangement, the yoke thin film magnetic 
head of the present invention enables a point where discontinuities occur 
to be moved to the abscissa of the .DELTA.R/R curve, that is, to either 
the positive side or the negative side of the magnetic field Ha 
corresponding to the magnetic field of signals. Therefore, when the 
operating point of the MR element 2 is moved by the biasing magnetic field 
to a point good at linearity, and if such operating point is at the side 
where no discontinuities occur in the magnetic field Ha, it becomes 
possible to suppress the switching of magnetization which would take place 
in the magnetic field are in the same polarity as the biasing magnetic 
field. Consequently, the generation of Barkhausen noises resulting from 
the switching of magnetization can be suppressed, thereby eventually to 
make output signals reproduced by the yoke thin film magnetic head high in 
quality. 
A yoke thin film magnetic head according to a second embodiment of the 
present invention will be described with reference to FIGS. 10 to 14. 
The yoke thin film magnetic head of the second embodiment of the present 
invention includes, as shown in FIG. 10, a first insulation layer 12 of a 
predetermined thickness placed onto a high magnetic permeability substrate 
11 which is made of, for example, Ni-Zn ferrite substrate, a conductor 14 
to apply bias magnetic field to MR element formed on the first insulation 
layer 12, and a second insulation layer 13 so formed onto the conductor 14 
as to hide the conductor 14. The yoke thin film magnetic head is further 
provided with a magnetic resistance effect element 15 (referred to as an 
MR element hereinbelow) on the second insulation layer 13, (which is made 
of a ferromagnetic film such as Ni-Fe film, Ni-Co film, etc.) The 
ferromagnetic film of Ni-Fe or Ni-Co, etc. referred to above has generally 
a finite magnetostriction constant. On the MR element 15 is formed a gap 
insulation layer 16 in such manner as to cover the first insulation layer 
12 and the second insulation layer 13. A first yoke 17 and a second yoke 
18 provided on the gap insulation layer 16 constitute an introduction path 
(a magnetic gap) for introducing the magnetic flux of signals generated 
from a magnetic recording medium 21 to the MR element 15. First yoke 17 
and MR element 15 and second yoke 18 and substrate 11 are so arranged as 
to form a closed magnetic circuit sequentially. There are formed 
evaporated meal films 19 and 20 (films for cancelling the residual stress 
in the yokes 17, 18) having high melting points onto the yokes 17 and 18. 
The films 19 and 20 have generally the same configuration as the yokes 17 
and 18. For the metal having high melting points, Mo, Nb, Ta, Hf, Ti, Cr, 
V or the like is employed. 
The yokes 17 and 18 are coated with a ferromagnetic film of Ni-Fe or Ni-Co 
by sputtering. For example, the thickness of the ferromagnetic film is 
about 0.6 .mu.m. In this case, for the purpose of achieving favorable 
magnetic properties (high magnetic permeability, low coercive force) 
required for the yokes, negative substrate biasing voltage needs to be 
applied during the sputtering. Moreover, according to the second 
embodiment of the present invention, before the coated Ni-Fe film is 
processed into the shape of a yoke, a film having high melting points made 
of, for example, Mo or Nb described above is coated onto the Ni-Fe film by 
evaporation. Thereafter, both the Ni-Fe film and the evaporated metal film 
are processed into the shape of a yoke at one time by ion milling to be 
the first and the second yokes 17 and 18, and the evaporated metal films 
having high melting points 19 and 20, respectively. 
The internal stress in the yokes 17 and 18, and in the MR elements of the 
thin film magnetic head of FIG. 10 is illustrated in FIG. 11, in which 
.delta..sub.y represents the compressive stress of the yokes 17 and 18, 
namely, the sputtered Ni-Fe films, and .delta..sub.c represents the 
tensile stress of the stress cancel film 19, that is, the evaporated Ni-Fe 
film. Since the stress applied to the MR element 15 by the yokes 17 and 18 
is in proportional relation to (.delta..sub.y -.delta..sub.c), it becomes 
possible to considerably reduce the stress generated in the MR element 15 
if .delta..sub.y is selected to establish .delta..sub.y 
.perspectiveto..delta..sub.c. 
The internal stress of the sputtered Ni-Fe film on the yokes 17 and 18 
employed in the second embodiment was approximately -7.times.10.sup.9 
dyne/cm.sup.2, while that of the evaporated Ni-Fe film of the stress 
cancel film 19 was approximately +15.times.10.sup.9 dyne/cm.sup.2. 
Accordingly, the stress against the MR element 15 applied by the 
two-layered film of the yokes 17 and 18, and the stress cancel film 19 
could be remarkably reduced by laying evaporated Ni-Fe films, each having 
the thickness of half of the sputtered Ni-Fe film, one after another, as 
shown in FIG. 12. Referring to FIG. 12 which is a vertical cross sectional 
view in the widthwise direction of the track of the head, the yokes 17 and 
18 are layered with stress cancel films 19 and 20 each having the 
thickness of half of the yokes 17 and 18, respectively, such that the 
stress applied to the MR element 15 by the yokes 17 and 18 is cancelled on 
the whole. 
The Ni-Fe film thus formed by application of the negative substrate biasing 
voltage has the internal compressive stress .delta..sub.c of about 
1.times.10.sup.10 dyne/cm.sup.2 dis-anisotropically, as shown in FIG. 11. 
On the other hand, in the evaporated metal films 19 and 20 made of Mo, Nb 
or the like, also as shown in FIG. 11, dis-anisotropically exists the 
internal stress .delta..sub.y of about 1.2.times.10.sup.10 dyne/cm.sup.2 
in the extending direction (with reference to "Thin Film Handbook", p. 
341-342, published by Ohm Publishing Co., Ltd.). Accordingly, since the 
internal compressive stress present in the first and second yokes 17 and 
18, and the internal tensile stress in the evaporated metal films 19 and 
20 are repulsive with each other, the stress (.delta..sub.y 
-.delta..sub.c) applied to the MR element 15 becomes substantially zero, 
or reduced on a large scale in comparison with the prior art. As a result 
of this, the magnetic anisotropy can be prevented from being disturbed, 
thereby to suppress the generation of Barkhausen noises as much as 
possible. It is to be noted here that although the evaporated metal films 
having high melting points and made of Mo or Nb, etc. are approximately of 
the same thickness as the Ni-Fe film, it is necessary to make the 
evaporated metal films, if they are made of material other than Mo and Nb, 
more thick than the films made of Mo or Nb since the internal tensile 
stress of such evaporated films made of material than Mo and Nb is 
relatively small. Accordingly, when the readiness for processing of the 
yokes is taken into consideration, it is most desirable to employ the 
evaporated metal films made of Mo or Nb described above. Furthermore, 
since the evaporated metal film 19 is eventually exposed to the sliding 
surface side of the magnetic recording medium 21, in conjunction with an 
end portion of the yoke 17, it is important that the film 19 is highly 
resistive against corrosion in order to improve the reliability of the YMR 
head. From the above-described viewpoint of resistivity against corrosion 
also, it can be said that the evaporated metal film made of Mo or Nb is 
superior. 
Referring to a graph of FIG. 14, there is shown the internal stress in the 
sputtered Ni-Fe film formed by a three electrode sputtering device in 
which the target current and the target object can be controlled 
independently from each other, and the magnetic permeability of the 
sputtered Ni-Fe film formed onto the substrate having unevenness of 2 
.mu.m (the same condition as the YMR head) by the three electrode 
sputtering device. When the substrate biasing voltage is in the range of 
0-150 V, the direction of the easy axis of the magnetic anisotropy in the 
Ni-Fe film is vertical to the film surface. Therefore, the magnetic 
permeability is low, and the Ni-Fe film cannot be used for the yoke film. 
When the substrate biasing voltage is less than -150 V, the direction of 
the easy axis in the Ni-Fe film becomes horizontal to the film surface, 
with the magnetic permeability being raised in accordance with the 
decrease of the substrate biasing voltage, and accordingly, Ni-Fe film 
which can be used as the yoke is the Ni-Fe film which is applied with the 
substrate biasing voltage lower than -150 V. If the substrate biasing 
voltage becomes below -150 V, the internal compressive stress in the Ni-Fe 
film exceeds 8.times.10.sup.9 dyne/cm.sup.2, and thereafter, the internal 
compressive stress gradually increases in accordance with the decrease of 
the substrate biasing voltage. As described above, the internal 
compressive stress in the sputtered Ni-Fe film changes in accordance with 
the change in the substrate biasing voltage. However, the total internal 
tensile stress in the evaporated metal film can be easily changed by 
changing the thickness of the evaporated metal film, the change of the 
internal compressive stress in the sputtered Ni-Fe film can be coped with 
easily. Accordingly, it becomes possible to set conditions for sputtering 
the Ni-Fe film desirably, without any limitations imposed by the internal 
stress of the Ni-Fe film. Thus, the Ni-Fe film can be formed with such 
conditions that can render the magnetic properties of the Ni-Fe film most 
excellent, resulting not only in suppression of Barkhausen noises, but in 
realization of a YMR head high in sensibility. 
FIG. 13 shows an example that the thin film magnetic head of the present 
invention and the prior art thin film magnetic head are arranged in 
parallel onto a single substrate. In the drawing, each chip is constituted 
by a head having 20 tracks. 8chips shown by oblique lines are constructed 
in accordance with the present invention, while the remaining 8 chips are 
constructed according to the prior art, both fabricated from the same 
substrate. In the manner as above, Barkhausen noises appear on 87 tracks 
among 160 tracks (20.times.8=160) in the thin film magnetic head of the 
present invention. On the other hand, there are 140 tracks among 160 
tracks on which Barkhausen noises are generated in the known thin film 
magnetic head. Thus, according to the present invention, the thin film 
magnetic head can be distinguishably free from the Barkhausen noises. 
Although the yokes 17 and 18 are Ni-Fe films formed by sputtering, and the 
stress cancel films 19 and 19 are Ni-Fe films formed by vaporization in 
the second embodiment, the reverse combination of the films may be 
possible. Further, various other combinations for the yokes 17 and 18 and, 
the stress cancel films 19 and 19 can be employed. 
In other words, for the yoke films 17 and 18, the following may be 
applicable: Ni-Fe film (compressive stress), evaporated Fe-Al-Si film 
(tensile stress), sputtered Fe-Al-Si film (compressive or tensile stress), 
evaporated amorphous film (tensile stress) in which Co contains about 
10-20% of such semi-metal as Si, B and P or such metal as Zr, Ti, Nb, Ta, 
Hf or W, sputtered amorphous film (compressive stress) in which Co 
contains approximately 10-20% of such semi-metal as Si, B or P, or 
transition metal such as ZR, Ti, Nb, Ta, Hf or W. On the other hand, for 
the stress cancel films 19 and 19, evaporated metal film (tensile stress) 
made of W, Ti, Ta, Zr, Nb, Hf or the like, sputtered metal film 
(compressive stress) made of W, Ti, Ta, Zr, Nb, Hf, etc., sputtered 
insulation film (compressive stress) made of SiO.sub.2, Al.sub.2 O.sub.3, 
Si.sub.3 N.sub.4 or the like can be employed, in addition to the 
aforementioned films applicable for the yoke films 17 and 18. However, it 
is needless to say that it is necessary that the polarity of the stress in 
the films 17 and 18 should be opposite to that in the films 19 and 19. 
The yoke thin film magnetic head according to the present invention is, as 
has been described hereinabove with reference to the second embodiment 
thereof, provided with yokes placed for leading the magnetic flux of 
signals generated from the magnetic recording medium up to the MR element. 
The yokes are made of sputtered films to hold the compressive stress 
therein. Moreover, the yoke thin film magnetic head has evaporated metal 
films formed onto the yokes. Since the evaporated metal films have 
internal tensile stress approximately equal to the internal compressive 
stress of the yokes, the internal compressive stress generated in the 
yokes can be substantially negated or reduced. Thus, the disturbance of 
the magnetic anisotropy in the MR element caused by the residual stress in 
the yokes can be suppressed, and at the same time Barkhausen noises can be 
made small. Moreover, the conditions for sputtering the yoke material can 
be suitably set, with no limitations imposed by the internal stress of the 
material. Therefore, it becomes possible to prepare the yoke film by 
sputtering under the condition that the magnetic properties of the 
material can be rendered best. Accordingly, the yoke thin film magnetic 
head of the present invention can be highly sensitive. 
A third embodiment of the present invention will be described with 
reference to FIGS. 15 to 18. 
As shown in FIG. 15, a YMR head according to the third embodiment has, at 
one end 31a of a substrate 31, a sliding surface to be slid with a 
magnetic recording medium 32. The substrate 31 constituting a lower yoke 
is made of a ferrite substrate such as polycrystal Ni-Zn ferrite substrate 
or, a single crystal or polycrystal Mn-Zn ferrite substrate, or a high 
magnetic permeability substrate having a high magnetic permeability thin 
film like Ni-Fe, Fe-Al-Si or Co-Zr layered onto a non-magnetic substrate. 
For example, since the YMR head generally has many tracks, the width of a 
track of the magnetic recording medium 32 is set to be approximately 50 
.mu.m. An insulation layer 33 made of SiO.sub.2, etc. is formed on the 
substrate 31 near the end surface 31a, with a magneto-resistive element 
(referred to as an MR element) 34 being put on the insulation layer 33. 
The MR element 34 is made of a ferromagnetic film such as Ni-Fe film or 
Ni-Co film, etc., having the thickness of 200 .ANG.-1000 .ANG., and the 
length approximately equal to the track width of the magnetic recording 
medium 32. Moreover, the MR element 34 has a positive or negative 
magnetostriction constant to correspond to the polarity of the residual 
stress, either to the compressive stress or to the tensile stress, 
generated in the upper yokes 36 and 37 which will be described later. 
Therefore, in the case where the internal stress .delta..sub.y of the 
upper yokes 36 and 37 is tensile, namely positive, the magnetostriction 
constant to the MR element is set to be negative. On the contrary, in the 
case where the internal stress .delta..sub.y is compressive, namely 
negative, the magnetostriction constant .lambda..sub.s is set to be 
positive. Furthermore, upon fabricating the MR element 34, the easy 
magnetization axis in the MR element 34 is selected in the longitudinal 
direction of the MR element 34. When a sense current I.sub.s runs in the 
longitudinal direction of the MR element 34, the MR element 34 converts 
the magnetic field of signals from the magnetic recording medium 32 into 
the change in voltage at opposite ends of the MR element 34. On the 
substrate 31, the insulation layer 33 and the MR element 34, there is 
formed a gap insulation film 35 in such manner as to cover the substrate 
31, the layer 33 and the element 34. This gap insulation film 35 is made 
of SiO.sub.2 or the like. An upper yoke 36 which is a first yoke and an 
upper yoke 37 which is a second yoke are placed opposite to each other, 
with a gap therebetween, on the gap insulation film 35. The ferromagnetic 
upper yokes 36 and 37 generally made of permalloy films having the 
thickness of approximately 0.5-4.0 .mu.m constitute a magnetic path for 
magnetic recording signals detected from the magnetic recording medium 32. 
The upper yoke 36, the MR element 34 and the upper yoke 37 are 
magnetically connected to each other in this order. 
In the YMR head, it is so arranged that, if a current I.sub.B for applying 
biasing magnetic field is sent into a biasing conductor (not shown), the 
MR element 34 is given with a desired biasing magnetic field, such that 
the operating point of the MR element 34 is moved to a point good at 
linearity. 
In the above-described arrangement, the predetermined magnetostriction 
constant .lambda..sub.s is set for the MR element 34 as mentioned earlier, 
which can be determined depending on the conditions how the MR element 34 
is fabricated. By way of example, however, if the MR element 34 is made of 
Ni-Fe film except when it contains 79-82 wt % of Ni therein, the 
magnetostriction constant .lambda..sub.s of the MR element 34 is changed 
by the influences of the crystal orientation of the Ni-Fe film, and 
therefore it is difficult to prepare the Ni-Fe film in such manner as to 
make the magnetostriction constant .lambda..sub.s to be zero (with 
reference to J. Appln. Phys. 52(3), March 1981, P2474-2476 "The Saturation 
Magnetostriction of Permalloy Film"). On the contrary, it is easy to 
fabricate the MR element 34 in such manner that the magnetostriction 
constant of the Ni-Fe film is controlled to be either positive or negative 
of the magnetostriction constant .lambda..sub.s of the MR element 34. 
Accordingly, if the polarity of the magnetostriction constant 
.lambda..sub.s of the film of the MR element 34 is selected in 
correspondence to the polarity of the internal stress .delta..sub.y in the 
upper yokes 36 and 37, the magnetostriction effect is generated in the MR 
element of the yoke film, thereby to lessen the influences by residual 
stress of the yoke film. In this case, it is supposed that when 
.delta..sub.y is positive, the tensile stress is generated in the film of 
the upper yokes 36 and 37, while when .delta..sub.y is negative, the 
compressive stress is generated in the film of the upper yokes 36 and 37. 
In other words, in the case where the polarity of the internal stress 
.delta..sub.y of the film of upper yokes 36 and 37 is negative, the 
external stresses .delta..sub.MR and .delta.'.sub.MR applied to the MR 
element 34 as the result of the reaction to the internal stress 
.delta..sub.y work, as shown in FIG. 16, as tensile stress in the 
longitudinal direction and compressive stress in the widthwise direction 
of the MR element. It is to be noted here that .delta..sub.MR represents 
the stress in the longitudinal direction of the MR element 34, and 
.delta.'.sub.MR represents the stress in the widthwise direction of the MR 
element 34. In the case where the internal stress .delta..sub.y in the 
film of the upper yokes 36 and 37 is directed in the positive direction, 
the external stress .delta..sub.MR and .delta.'.sub.MR applied to the MR 
element 34 as the reaction to the internal stress .delta..sub.y are, as 
shown in FIG. 17, compressive stress in the longitudinal direction, and 
tensile stress in the widthwise direction. Therefore, by arranging the 
relationship between the internal stress .delta..sub.y in the film of the 
upper yokes 36 and 37, and the magnetostriction constant .delta..sub.s of 
the MR element 34 as follows: 
EQU when .delta..sub.y &lt;0, .delta..sub.s &gt;0 and 
EQU when .delta..sub.y &gt;0, .delta..sub.s &lt;0, 
the magnetic anisotropy L-L' of the MR element 34 induced by the stress of 
the upper yokes 36 and 37 is in the longitudinal direction of the MR 
element 34. Since the direction of this magnetic anisotropy L-L' is 
coincident to the direction of magnetic anisotropy K-K' induced when the 
MR element is fabricated, the composed magnetic anisotropy M-M' is also 
rendered coincident to the longitudinal direction of the MR element 34. In 
consequence to this, discontinuities are hardly generated in the 
magnetization within the MR element 34, and accordingly it becomes 
advantageous that the internal stress in the film of the upper yokes 36 
and 37 never affect the magnetic properties of the MR element 34 by 
Barkhausen noises, etc. 
Showing a concrete example, when the upper yokes 36 and 37 are made of 
sputtered Ni-Fe film or sputtered Co-Cr film, since the stress in the 
upper yokes 36 and 37 are generally compressive stress, the 
magnetostriction constant .lambda..sub.s of the MR element 34 is set to be 
positive. Further, when the upper yokes 36 and 37 are made of evaporated 
Ni-Fe film or plated Ni-Fe film, the stress in the upper yokes 36 and 37 
is tensile stress, and accordingly, the magnetostriction constant 
.lambda..sub.s of the MR element 34 is set to be negative. Similarly, when 
the materials other than the aforementioned materials are used for the 
upper yokes 36 and 37, the magnetostriction constant .lambda..sub.s of the 
MR element 34 is determined selectively to be positive or negative in 
correspondence to the stress generated in the yoke material. 
As has been described hereinabove, the reluctance effect thin film head, 
i.e., the YMR head according to the third embodiment of the present 
invention has the first yoke, the MR element and the second yoke, all made 
of ferromagnetic thin films, magnetically connected to each other 
sequentially in this order. The reluctance effect thin film head is so 
constructed that when the internal stress generated in the first and the 
second yokes is positive, the magnetostriction constant of the MR element 
is set to be negative, while, when the internal stress generated in the 
first and the second yokes is negative, the magnetostriction constant of 
the MR element is set to be positive. Because of the above-described 
construction, the direction of the magnetic anisotropy of the MR element 
induced by the internal stress in the first and the second yokes can be 
made coincident to the direction of the magnetic anisotropy induced when 
the MR element is fabricated. As a result, the anisotropy in the MR 
element can be prevented from being dispersed, thereby to reduce 
Barkhausen noises. Accordingly, the reluctance effect thin film head with 
high fidelity can be realized.