Thin film magnetic head having magnetic film of Co-Ni-Fe alloy

A thin film magnetic head comprising a lower magnetic film, an upper magnetic film which is formed over the lower magnetic film and in which one end is come into contact with one end of the lower magnetic film and the other end faces the other end of the lower magnetic film through a magnetic gap and thereby forming a magnetic circuit which has a magnetic gap in a part thereof, together with the lower magnetic film, and a conductor coil forming a coil of a predetermined number of turns and passing between the upper and lower magnetic films and crossing the magnetic circuit. Each of the upper and lower magnetic films is formed of a Co-Ni-Fe ternary alloy having a face-centered cubic crystal structure. Also, uniaxial anisotropy is alternately and perpendicularly given in every layer of a predetermined thickness stacked in the direction of thickness of the film.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thin film magnetic head and, more 
particularly, to a thin film magnetic head suitable for use in a magnetic 
disk apparatus. 
Particularly, the present invention has a feature in a magnetic core. 
2. Description of the Prior Art 
Hitherto, Permalloy, which is a binary alloy of nickel of about 80 weight % 
and iron of about 20 weight %, has been used as a magnetic core material 
for thin film magnetic heads. This material has an almost null 
magneto-striction coefficient and a high magnetic permeability in the high 
frequency region. Therefore, the thin film magnetic head using this 
magnetic core material has excellent readout performance. 
However, the saturation magnetic flux density of Permalloy is low, i.e. 
about one tesla. Thus, the writing performance of the thin film magnetic 
head using the magnetic core of Permalloy is not high. Practically 
speaking, in magnetic disk apparatuses, there is a tendency that a 
material having a high coercive force is used as a material of the 
recording medium from the viewpoint of realization of a high recording 
density. The thin film magnetic head having a magnetic core of Permalloy 
has degraded writing performance to the recording medium of a high 
coercive force. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a thin film magnetic 
head provided with a magnetic core having a high permeability, an almost 
null magneto-striction coefficient and a higher saturation magnetic flux 
density than Permalloy and, therefore, is excellent in both readout 
performance and writing performance. 
The present invention relates to a thin film magnetic head comprising: a 
lower magnetic film; an upper magnetic film, formed over the lower 
magnetic film in which one end of the upper magnetic film comes into 
contact with one end of the lower magnetic film and the other end faces 
the other end of the lower magnetic film through a magnetic gap, thereby 
forming a magnetic circuit, a part of which has a magnetic gap together 
with the lower magnetic film; and a conductor coil forming a coil of 
predetermined turns which passes between the upper and lower magnetic 
films and crosses the magnetic circuit. This thin film magnetic head is 
characterized in that each of the upper and lower magnetic films contains 
at least 97 weight % of a cobalt alloy comprising cobalt (Co) of 62-95 
weight %, nickel (Ni) of 3-30 weight %, and iron (Fe) of 2-8 weight % and 
has a face-centered cubic crystal structure. Further, uniaxial anisotropy 
is alternately perpendicularly given for every layer of a predetermined 
thickness stacked in the direction of thickness of the film, e.g. in a 
manner as x-y-x-y . . . . 
As physical properties of a core material for the thin film magnetic head 
which can realize a high recording density in magnetic recording, there 
are needed magnetic properties comparable to those of the thin Permalloy 
film; i.e. an anisotropic magnetic field of 2 to 5 oersteds, an extremely 
small magneto-striction coefficient, namely, +2.times.10.sup.-6 to 
-2.times.10.sup.-6 and a low coercive force below one oersted; and a high 
saturation magnetic flux density as compared with one tesla of the thin 
Permalloy film, namely at least 1.3 teslas. 
The present inventors have paid attention to the fact that a Co-Ni-Fe 
ternary alloy bulk material has a high saturation magnetic flux density 
and almost zero magneto-striction coefficient and studied the film 
structure and film composition range which are suitable to make the 
anisotropic magnetic field as small as that of the thin Permalloy film. 
Regarding the Co-Ni-Fe alloy, Bozorth, "Ferromagnetism," published by Van 
Nostrand, Vol. 4, page 165, which is incorporated by reference herein, 
sets forth the fact that the saturation magnetic flux density becomes 
larger than that of Permalloy within the composition range where the 
magneto-striction coefficient becomes near zero, namely, the composition 
range of 0-80 weight % Ni, 0-90 weight % Co, and 0-20 weight % Fe. 
There has also been reported in IEEE Transactions on Magnetics, Vol. 
MAG-19, (1983), pages 131-135, which is incorporated by reference herein, 
the fact that the magnetic permeability can be raised by performing a 
thermal treatment in a rotating magnetic field after producing a Co base 
alloy film. 
However, although these articles suggest amorphous Co base alloy films, 
nothing is disclosed with respect to the thermal treatment effect in the 
rotating magnetic field with regard to the crystalline alloy film. 
The upper and lower magnetic films in the magnetic head of the present 
invention are manufactured by depositing Co-Ni-Fe ternary alloys on a 
substrate while alternately applying the magnetic field at a predetermined 
frequency in paralel with the substrate surface in the directions which 
cross perpendicularly with each other, namely, by forming the magnetic 
films in the orthogonal switching magnetic field. 
On one hand, if the method of manufacturing the magnetic films in the 
orthogonal switching magnetic field is applied to Permalloy evaporated 
films, this will increase the anisotropic dispersion and may cause the 
coersive force to be increased. Thus, this method is undesirable as a 
method for manufacturing the magnetic core for a thin film magnetic head. 
In other words, applying the orthogonal switching magnetic field to the 
thin Permalloy film results in an undesirable effect. 
A reason why the composition range of the Co-Ni-Fe ternary alloy thin film 
is limited is because if the content of Co is less than 62 weight %, the 
saturation magnetic flux density becomes below 1.3 teslas, so that the 
performance as a high saturation magnetic flux density cannot be achieved; 
on the contrary, if the content of Co is larger than 95 weight %, the 
coercive force becomes large, so that realization of a high permeability 
cannot be expected. It is preferable to select the comosition of Co at 
least 72 weight %. 
Ni is concerned with the saturation magnetic flux density together with Co 
and if its content is over 30 weight %, the flux density becomes below 1.3 
teslas, while if it is less than 3 weight %, the magneto-striction 
coefficient is shifted to the positive side and becomes higher than 
+2.0.times.10.sup.-6. It is particularly preferable to select the Ni 
composition at least 12 weight % and at most 22 weight %. 
Fe most strongly influences on the magnetostriction coefficient and if the 
content of Fe is less than 2 weight % under the condition whereby a high 
saturation magnetic flux density is secured while the contents of Co and 
Ni are set within the above-mentioned proper ranges, the magneto-striction 
coefficient is largely shifted to the negative side and becomes lower than 
-2.times.10.sup.-6. On the contrary, if the content of Fe is larger than 8 
weight %, the magneto-striction coefficient is largely shifted to the 
positive side and becomes higher than +2.times.10.sup.-6. 
For the foregoing reasons, the compositions of the Co-Ni-Fe alloy are 
selected such that Co is 62-95 weight %, Ni is 3-30 weight %, and Fe is 
2-8 weight %. 
The preferable compositions of the Co-Ni-Fe alloy are such that Ni is 12-22 
weight %, Fe is 2-8 weight %, and the residual composition consists of Co 
of at least 72 weight %. 
The upper and lower magnetic films in the thin film magnetic head of the 
present invention may contain a small quantity of the fourth component in 
addition to Co, Ni and Fe. As the fourth component, at least one element 
selected from boron (B), indium (In), antimony (Sb), and bismuth (Bi) is 
suitably used. The total amount of the fourth component should not exceed 
3 weight %. In the case where the fourth component is contained, the total 
effective quantity is at least 0.05 weight %. Therefore, when the fourth 
component is positively contained, its content should be within a range of 
0.05 to 3 weight % in total. 
Addition of B to the Co-Ni-Fe alloy makes it possible to further reduce the 
coercive force and to improve the readout performance of the thin film 
magnetic head. It is preferable to select the content of B at 0.05-0.5 
weight %. If the content of B is less than 0.05 weight %, the reducing 
effect of the coercive force becomes small. Contrarily, if it is larger 
than 0.5 weight %, the film quality is degraded. 
At least one of In, Sb and Bi as the fourth component has the effect of 
raising the heat-resisting property of the Co-Ni-Fe alloy thin film. It is 
essential that the fourth component is selected from those which do not 
form solid solution with the Co-Ni-Fe alloy base but are precipitated at 
the crystal grain boundaries. Solid-solution of the fourth component in 
the Co-Ni-Fe alloy base may cause large variations in magneto-striction 
coefficient, saturation magnetic flux density, coercive force, etc., so 
that it is undesirable. 
It is preferable to form the Co-Ni-Fe ternary alloy thin film according to 
the present invention by depositing it on a substrate by way of plating. 
The most suitable method by way of plating is realized in the following 
manner. Electroplating is performed with a plating current density of 6-30 
mA/cm.sup.2 using the plating solution having a pH of 2.5 to 3.5 and held 
at temperatures of 20.degree. to 35.degree. C. in which the Co.sup.++ ion 
concentration is 3-20 g/l, the Ni.sup.++ ion concentration is 10-30 g/l 
and the Fe.sup.+ ion concentration is 0.2-1.0 g/l. The plating is 
performed while alternately (sequentially) applying crossed external 
magnetic fields at a predetermined frequency parallel to the plating 
surface in the directions which are perpendicular to each other during the 
plating process. 
To test the present invention, depositing by plating was mainly adopted. 
Hydrated cobalt sulfate of the concentration of 20-70 g/l was used as a Co 
source. Hydrated nickel chloride or hydrated nickel sulfate and a solution 
in which they coexist were used as a Ni source which has the concentration 
of 10-90 g/l. Hydrated ferrous sulfate of the concentration of 1-5 g/l was 
used as a Fe source. In addition to those components, a proper quantity of 
boric acid was added as a pH buffer agent during plating. A proper 
quantity of saccharin sodium was added as a stress relaxation agent of the 
plated film. A proper quantity of lauryl sodium sulfate was added as a 
surface active agent. 
The temperature of the plating solution was set to 25.degree.-35.degree. C. 
The plating current density was changed in the range of 10-30 mA/cm.sup.2. 
The value of pH was set to 2.5-3.5. 
The orthogonal switching magnetic fields of 30 to 60 Oe were respectively 
applied by Helmholtz coils at a repetitive frequency of 1 to 10 Hz to the 
thin film of the Co-Ni-Fe ternary system during the plating, in which 
pairs of Helmholtz coils, each pair sandwiching the substrate, were 
disposed in parallel with the substrate and perpendicularly with each 
other. 
Good Co-Ni-Fe ternary alloy thin films were obtained by plating under the 
conditions of the above ranges, which presented a uniaxial anisotropy and 
had an anisotropic magnetic field below 10 Oe. 
Meanwhile, it is possible to obtain films having a uniaxial anisotropy by 
applying other kinds of external magnetic fields or a unidirectional 
external magnetic field, but they are not preferable since the anisotropic 
magnetic field becomes too large, e.g. over 20 Oe. It is possible to 
obtain magnetic thin films exhibiting uniaxial anisotropy and small 
anisotropic magnetic field by repeatedly applying external magnetic fields 
at a predetermined frequency onto the substrate for deposition of the 
plated film in orthogonal directions. Further, proper selections of the 
repetitive frequency and the ratio of the periods of time during which the 
respective orthogonal magnetic fields of X-Y directions are applied makes 
it possible to reduce the anisotropic magnetic field of the magnetic film 
to 10 Oe or below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Example 1 
An ordinary glass substrate having a diameter of 3 inches and a thickness 
of 0.5 mm was used as a substrate. First, after the substrate was 
sufficiently cleaned by boiling ultrasonic cleaning in trichloroethylene, 
Permalloy is deposited by sputtering or vacuum deposition to a thickness 
of 0.1 .mu.m to form the underlayer substrate for plating. 
The substrate with the underlayer film was attached to a jig in the plating 
bath and the bath was filled with a Co-Ni-Fe electroplating solution of 
the following compositions, then it was circulated and stirred. 
CoSO.sub.4 .multidot.7H.sub.2 O:45 g/l 
NiCl.sub.2 .multidot.6H.sub.2 O:60 g/l 
NiSO.sub.4 .multidot.6H.sub.2 O:25 g/l 
FeSO.sub.4 .multidot.7H.sub.2 O:2.0 g/l 
Boric acid:25 g/l 
Saccharin sodium:1.5 g/l 
Lauryl sodium sulfate:0.15 g/l 
The plating current controlled to 17 mA/cm.sup.2 was allowed to flow 
between the anode (Ni) and the cathode (substrate). The temperature of the 
bath was set to 30.degree. C. and pH was controlled to 3.0. During the 
plating, orthogonal switching magnetic fields were applied at a repetitive 
frequency of 5 Hz, the applied magnetic fields in the X direction 
(direction of an axis of easy magnetization) and the Y direction 
(direction of an axis of difficult magnetization) were 30 Oe, and the 
ratio of the repetitive pulse widths in the X and Y directions is 6:4. 
For the purpose of comparison, the film plated in the conventionally 
employed unidirectional magnetic field instead of the orthogonal switching 
magnetic field was estimated as well. The film thickness was 1.5 .mu.m. 
FIGS. 1 and 2 show B-H curves of the magnetic thin films obtained in the 
above manner according to the present invention and to the conventional 
method. In FIGS. 1 and 2, reference numeral 100 denotes the B-H curve in 
the direction of an axis of easy magnetization, and 200 indicates the B-H 
curve in the direction of an axis of difficult magnetization. Other 
magnetic characteristics and film compositions of the present example 
according to the present invention are as shown in Table 1. 
TABLE 1 
______________________________________ 
Film compositions 
(weight %) 78% Co--16% Ni--6% Fe 
______________________________________ 
Saturation magnetic 
1.53 teslas 
flux density 
Coercive force in the 
1 oersted 
direction of an axis of 
difficult magnetization 
Anisotropic magnetic field 
6 oersteds 
Magneto-striction 0.8 .times. 10.sup.-6 
coefficient 
______________________________________ 
As is obvious from the above-mentioned results, the magnetic thin film 
according to the present invention exhibits uniaxial anisotropy with a 
small anisotropic magnetic field, and very high saturation magnetic flux 
density of 1.5 teslas, which value is 1.5 times as high as that of a 
conventional binary Permalloy. It has been found that the magnetic thin 
film of the comparison example showed a similar saturation magnetic flux 
density of 1.5 teslas, but a larger anitostropic magnetic field of about 
20 Oe, which value was about three times as large as that of the magnetic 
thin film according to the invention. 
Example 2 
A substrate shown in Example 1 was attached to the same plating bath and 
was immersed in a Co-Ni-Fe electroplating solution containing: 
CoSO.sub.4 .multidot.7H.sub.2 O:35 g/l 
NiCl.sub.2 .multidot.6H.sub.2 O:85 g/l 
FeSO.sub.4 .multidot.6H.sub.2 O:2.0 g/l 
Boric acid:25 g/l 
Saccharin sodium:1.5 g/l 
Lauryl sodium sulfate:0.1 g/l 
Electroplating was performed while circulating and stirring the 
electroplating solution. A plating current controlled to 10 mA/cm.sup.2 
was allowed to flow between the anode (Ni) and the cathode (substrate). 
The temperature of the bath was set to 30.degree. C. and pH was controlled 
to 3.0. During the plating, orthogonal switching magnetic fields were 
alternately applied at a repetitive frequency of 1 Hz. Each of the applied 
magnetic fields in the X and Y directions was 45 Oe, and the ratio of the 
repetitive pulse widths in the X and Y fields was 5:5. The film thickness 
was 2.5 .mu.m. The B-H curve of the magnetic film according to the present 
example obtained in this manner had almost the same shape as in FIG. 1 and 
the anisotropic magnetic field was 9 Oe and the coercive force in the 
direction of an axis of difficult magntization was 0.9 Oe. Other magnetic 
characteristics and film compositions are as shown in Table 2. 
TABLE 2 
______________________________________ 
Film compositions 
(weight %) 74% Co--20% Ni--6% Fe 
______________________________________ 
Saturation magnetic 
1.50 teslas 
flux density 
Coercive force in the 
0.9 oersted 
direction of an axis of 
difficult magnetization 
Anisotropic magnetic 
9 oersteds 
field 
Magneto-striction 2 .times. 10.sup.-6 
coefficient 
______________________________________ 
Example 3 
A similar substrate as that described in Example 1 was attached to a jig in 
the plating bath and put in the Co-Ni-Fe electroplating solution 
containing: 
CoSO.sub.4 .multidot.7H.sub.2 O:55 g/l 
NiCl.sub.2 .multidot.6H.sub.2 O:60 g/l 
NiSO.sub.4 .multidot.6H.sub.2 O:25 g/l 
FeSO.sub.4 .multidot.7H.sub.2 O:2.5 g/l 
Boric acid:25 g/l 
Saccharin sodium:1.5 g/l 
Lauryl sodium sulfate:0.1 g/l 
The electroplating was performed while circulating and stirring the 
electroplating solution. A plating current controlled to 15 mA/cm.sup.2 
was allowed to flow between the anode (Ni) and the cathode (substrate). 
The temperature of the bath was set to 30.degree. C. and pH was controlled 
to 3.0. During the plating, orthogonal switching magnetic fields were 
alternately applied at a repetitive frequency of 3 Hz. Each of the applied 
magnetic fields in the X and Y directions was 40 Oe, and the ratio of the 
pulse widths in the X and Y fields was 6:4. The film thickness was 1.5 
.mu.m. 
The B-H curve of the magnetic film according to the present example 
obtained in this way had almost the same shape as in FIG. 1 and the 
anisotropic magnetic field was 6 Oe and the coercive force in the 
direction of an axis of difficult magnetization was 1 Oe. Magnetic 
characteristics are listed in Table 3. 
TABLE 3 
______________________________________ 
Film compositions 
(weight %) 82% Co--12% Ni--6% Fe 
______________________________________ 
Saturation magnetic 
1.60 teslas 
flux density 
Coercive force in the 
1.0 oersted 
direction of an axis of 
difficult magnetization 
Anisotropic magnetic 
6.0 oersteds 
field 
Magneto-striction -0.6 .times. 10.sup.-6 
coefficient 
______________________________________ 
As is obvious from the above results, the magnetic thin film according to 
the present example exhibited a uniaxial anisotropy with a small 
anisotropic magnetic field and a high saturation magnetic flux density 
over 1.5 teslas, so that realization of a high permeability can be 
expected. On the other hand, a magnetic film plated in the unidirectional 
magnetic field had a large anisotropic magnetic field about three or more 
times as large as that of the inventive film, so that the permeability was 
low and the readout voltage was insufficient when used in the thin film 
magnetic head or the like. 
Example 4 
A Permalloy thin film 2 (about 0.1 .mu.m) (see FIG. 3) is formed by 
sputtering as an underlayer film to perform plating on a ceramic substrate 
1 whose surface is sufficiently polished and cleaned. The Permalloy thin 
film 2 is connected as a cathode in the plating solution containing 
CoSO.sub.4 .multidot.7H.sub.2 O of 70 g/l, NiCl.sub.2 .multidot.6H.sub.2 O 
of 88 g/l and FeSO.sub.4 .multidot.7H.sub.2 O of 2.65 g/l as main 
components. The value of pH is controlled at 3.0 and the temperature of 
the bath is maintained at 30.degree. C. A lower magnetic film 3 is plated 
on the whole surface of the substrate in the bath using Ni as an anode 
with a current density of 17 mA/cm.sup.2 so as to have a thickness of 1.5 
.mu.m. The lower magnetic film 3 exhibits a high saturation magnetic flux 
density and contains Co of 82.2 weight %, Ni of 13.4 weight % and Fe of 
4.4 weight %. Next, the plated film together with the underlayer film is 
patterned to have a predetermined magnetic core shape by ion milling, wet 
etching or the like. Then, a gap material 4 such as Al.sub.2 O.sub.3 or 
the like, an organic insulation layer 5, a conductor coil 6, and a further 
organic insulation 5' are sequentially deposited by the film technology, 
and they are finished to have a predetermined shape by ion milling or wet 
etching. An underlayer film 2' is formed on the organic insulation 5' by 
sputtering similarly to the lower magnetic film 3. An upper magnetic film 
7 consisting of a material (82.2 weight % Co--13.4 weight % Ni--4.4 weight 
% Fe) of a high saturation magnetic flux density and having a thickness of 
about 2 .mu.m is plated on the underlayer film 2' in the same plating 
solution under the same conditions. The upper magnetic film 7 is likewise 
patterned to have the magnetic core shape by ion milling, wet etching, or 
the like. Thereafter, an insulation film such as Al.sub.2 O.sub.3 or the 
like is formed on the whole surface of the substrate by sputtering, 
thereby forming a protection film 8. Then, a block is cut out from the 
substrate 1 and the side of the magnetic head is ground to have a 
predetermined dimension to form a magnetic gap g, thereby forming a thin 
film magnetic head. FIG. 3 shows a cross sectional view of a part of the 
magnetic head obtained in this manner. FIG. 4 shows a perspective view of 
the thin film magnetic head cut out. 
In plating the lower and upper magnetic films, orthogonal switching 
magnetic fields were applied during the plating under the conditions that 
the repetitive frequency is 10 Hz and that the ratio of the periods of 
time during which the respective magnetization currents are allowed to 
flow through the orthogonal coils (this ratio is called a pulse width 
ratio) is 5.5:4.5. Magnetic characteristics of the plated film formed on a 
dummy substrate under the same conditions were excellent: the saturation 
magnetic flux density was 1.5 teslas, the anisotropic magnetic field was 5 
oersteds, and the magneto-striction coefficient was -0.5.times.10.sup.-6. 
It has been found that the anisotropic magnetic field according to the 
present invention was 5 oersteds, which value was reduced to about 1/6 as 
compared with the value of about 30 oersteds which has generally been 
reported. This is because the induced magnetic anisotropy of the film to 
be plated is alternately, sequentially and perpendicularly given by the 
orthogonal switching magnetic fields in every unit thickness in the 
direction of thickness which is determined by the film forming speed, 
repetitive frequency, and pulse width ratio. In the whole film, the 
anisotropic magnetic field appears as a mean and hence is reduced as 
compared with the film plated while applying a magnetic field in only one 
fixed direction. 
In the above examples, the lower and upper magnetic films were plated on 
the whole surface of the substrate and then patterned to have a core shape 
by ion milling. However, frame plating can also be performed using a 
resist frame which is formed to have a core shape. 
When comparing the electric characteristics of the thin film head produced 
in this manner with those of the head using a conventional thin Permalloy 
film, been confirmed that the writing and readout were improved by about 
30%. In particular, as distance, i.e. the spacing between the magnetic 
head the recording medium, increases, the difference in performance 
becomes more apparent. This means that the saturation magnetic flux 
density of the magnetic thin film according to the invention was increased 
by about 50% as compared with that of the thin Permalloy film. The 
magnetic thin film of the invention can sufficiently cope with the medium 
of a high coercive force for a high recording density. In addition, it has 
been found that the influence on the waveform distortion could be reduced 
by an amount commensurate with an increase in output. 
Explanation will then be made on the proper composition ranges of the 
foregoing thin film material of a high saturation magnetic flux density 
and on the process of reduction in the anisotropic magnetic field by the 
plating in orthogonal switching magnetic fields. 
As main compositions of the plating solution, CoSO.sub.4 .multidot.7H.sub.2 
O, NiSO.sub.4 .multidot.6H.sub.2 O (NiCl.sub.2 .multidot.6H.sub.2) may be 
mixed), and FeSO.sub.4 .multidot.7H.sub.2 O were used and their contents 
were changed within the ranges of 14-150 g/l, 40-200 g/l and 1-5 g/l, 
respectively. The pH was set to 3.0. The temperature of the bath was 
changed within the range of 20.degree.-35.degree. C. and the plating was 
performed within the range of the current density of 6-30 mA/cm.sup.2. The 
relationships among the compositions of the film, the saturation magnetic 
flux density, and the magneto-striction coefficient wer examined. In this 
way, proper composition ranges for producing preferred performances of the 
thin film magnetic head, i.e. a high saturation magnetic flux density and 
an almost zero magneto-striction coefficient, were found to be as shown in 
FIG. 5; over 72 weight % Co, below 22 weight % Ni, and 2-8 weight % Fe. 
However, if the content of Co is larger than 95 weight %, a hexagonal 
close-packed structure is formed, so that the coercive force becomes high 
and the magnetic characteristics become unstable. Therefore, the Co 
content is preferably not higher than 95 weight %. In this experiment, the 
plating was carried out in the ordinary unidirectional magnetic field, and 
the anisotropic magnetic field of the film exhibited high values of about 
20 oersteds. 
Then, orthogonal switching magnetic fields were applied during plating 
materials within the proper composition ranges to reduce the anisotropic 
magnetic field, and the characteristics of the plated films were examined. 
The compositions of the solution and the plating conditions are as follows. 
COMPOSITIONS OF THE SOLUTION 
CoSO.sub.4 .multidot.7H.sub.2 O:66.7 g/l 
NiSO.sub.4 .multidot.6H.sub.2 O:24.9 g/l 
NiCl.sub.2 .multidot.6H.sub.2 O:59.5 g/l 
FeSO.sub.4 .multidot.7H.sub.2 O:2.65 g/l 
Dimethylamine-borane:0.1 g/l 
Boric acid:25 g/l 
Saccharin sodium:1.5 g/l 
Lauryl sodium sulfate:0.1 g/l 
PLATING CONDITIONS 
pH:3.0 
Temperature of the bath:30.degree. C. 
Current density:17 mA/cm.sup.2 
ORTHOGONAL FIELD SWITCHING CONDITION 
Intensity of the magnetic field:50 oersteds 
Repetitive frequency:10 Hz 
Pulse width ratio:6:4 
The thickness of the plated film obtained was 2.0 .mu.m and the 
compositions were 82.2 weight % Co--13.0 weight % Ni--4.6 weight % Fe--0.2 
weight % B. The magnetic characteristics were excellent in that the 
saturation magnetic flux density was 1.56 teslas and the magneto-striction 
coefficient was 1.4.times.10.sup.-6. The uniaxial anisotropy was presented 
and the anisotropic magnetic field was low, i.e. 7 oersteds. FIG. 6 shows 
the B-H curve of the film formed in this way. FIG. 7 shows the B-H curve 
of the film plated in the ordinary unidirectional magnetic field. It has 
been found that the anisotropic magnetic field was reduced to about 1/3 as 
compared with that of the film plated in the ordinary unidirectional 
magnetic field. 
Next, the characteristics of the film plated within the same solution 
compositions and under the same plating condition while the orthogonal 
field switching condition was changed as described below were such that 
the film thickness was the same, 2 .mu.m, and the film compositions were 
also the same. 
ORTHOGONAL FIELD SWITCHING CONDITIONS 
Intensity of the magnetic field:50 oersteds 
Repetitive frequency:10 Hz 
Pulse width ratio:5.5:4.5 
Regarding the magnetic characteristics, the saturation magnetic flux 
density and magneto-striction coefficient exhibited the same values as 
those in the foregoing case since the compositions are the same. However, 
it has been found that the anisotropic magnetic field was fairly reduced 
to 5 oersteds. In addition, it has been found that dimethylamine-borane 
had the effect of reduction in coercive force. 
In addition to those results, the anisotropic magnetic fields of the films 
plated under various kinds of orthogonal field switching conditions ar 
shown in FIG. 8. 
As mentioned above, magnetic thin films according to the present invention 
can exhibit almost comparable performances in the magnetic characteristics 
required for a thin film magnetic head to those of a conventional thin 
Permalloy film, while they have high saturation magnetic flux density of 
no less than 1.5 teslas, which was increased by more than about 50% as 
compared with that of the thin Permalloy film. 
In applying orthogonal switching magnetic fields, even if the applying 
direction is deviated by about .+-.10.degree. from the orthogonal (90 
degrees) relation, the performance of the film is equally good. 
As described above, in the thin film magnetic head of the present 
invention, the upper and lower magnetic film essentially consist of the 
Co-Ni-Fe ternary alloy thin films and these thin films have the saturation 
magnetic flux densities higher than that of Permalloy and are equivalent 
to Permalloy in the magneto-striction coefficient and permeability. 
Consequently, according to the present invention, the writing performance 
is more excellent than that of the thin film magnetic head having upper 
and lower magnetic films formed of thin Permalloy films.