Method of the production of a magnetic head

In manufacturing a magnetic head having a magnetic circuit formed of magnetic material in which anisotropy can be induced, the magnetic head is processed by a first annealing process in a magnetic field for inducing anisotropy to generate an axis of easy magnetization in one direction in a part of the magnetic material, subsequently the magnetic head is processed by a second annealing process for annealing the magnetic material, applying the magnetic field in one of the directions perpendicular to the axis of the easy magnetization so as to relax the anisotropy induced by the first annealing process.

BACKGROUND IN THE INVENTION 
1. Field of the Invention 
The present invention relates to a method in the production of a magnetic 
head and more particularly to a method of annealing processing a magnetic 
head under a magnetic field. 
2. Description of the Prior Art 
There has been known to the public magnetic heads made using such a 
magnetic material that the magnetic anisotropy is induced under a magnetic 
field during an annealing process in at least a part of the magnetic head 
In the process of manufacturing the magnetic heads of the above type, 
there is generated a plurality of magnetic domains in the magnetic 
material, causing the permeability to be decreased due to generation of 
the magnetic anisotropy for stabilizing the magnetization in the magnetic 
domains and magnetic walls. In order to decrease the effect of the 
generation of the anisotropy, the magnetic material is usually subjected 
to an annealing process under a magnetic field. In the annealing process 
under the magnetic field, various experiments have been made to seek 
suitable processing conditions such as the magnetic directions and 
temperature and time of the annealing processing. Particularly, in order 
to manufacture the magnetic heads with good high frequency 
characteristics, it has been well known to orient the axis of easy 
magnetization of the anisotropy in a direction perpendicular to the 
direction of magnetic flux in the magnetic flux path of the magnetic head. 
Accordingly, in a magnetic head as shown in FIGS. 1 and 2, when forming a 
magnetic thin film 12, the direction of the magnetic field is oriented in 
the a direction of the width W of the head core. In FIGS. 1 and 2, 11 
denotes a substrate, 12 is the magnetic thin film made of Fe-Ni alloy, 13 
is a gap regulating film, 14 is a coil and 15 is an insulation film. 
In case magnetic anisotropy caused by the annealing is strong, a sufficient 
permeability can not be obtained. Therefore, there is required any kind of 
process to decrease the magnetic anisotropy. 
One known method of decreasing the magnetic anisotropy is to apply a 
rotation magnetic field onto a magnetic head assembly during the forming 
of the magnetic thin film on the substrate. However, the apparatus for 
applying the rotation magnetic field is very complicated and is not 
suitable for mass-production. 
Another method is to make the temperature during formation of the magnetic 
thin film as high as possible so as to decrease the magnetic anisotropy. 
In the case when the magnetic thin film is formed of a poly crystalline 
material, the grain diameter of the crystal becomes larger at the high 
temperature, thereby resulting in a decrement of the permeability. On the 
other hand, in case when the magnetic thin film is formed of an amorphous 
material, the amorphous material is crystallized in the high temperature 
range, resulting in a decrement of the permeability. Thus the second 
method is also not sufficient to obtain a good result 
In addition, there has been proposed another kind of magnetic head 
employing head cores made of amorphous magnetic material of the strip type 
formed by way of the rapid quenching method. In this method, it is 
difficult to control the magnetic anisotropy at the time of the production 
of the amorphous magnetic material. Therefore, the magnetic anisotropy is 
controlled by annealing under the magnetic field at the time immediately 
after production of the strip type amorphous magnetic material or after 
the magnetic core is formed. However, since the initial conditions of the 
amorphous material are different portion by portion of and/or product by 
product, it is difficult to control the magnetic anisotropy in a uniform 
manner. 
SUMMARY OF THE INVENTION 
An essential object of the present invention is to provide a method in the 
production of magnetic heads having good magnetic characteristics with a 
uniform quality. 
The present invention is directed to a method in the production of magnetic 
heads in which at least one portion of a magnetic circuit of the magnetic 
head is formed of the magnetic material in which the magnetic anisotropy 
is induced by an annealing process under the magnetic field. 
According to the present invention, the method includes a first annealing 
process with the magnetic field for orientation of the magnetizable axis 
of the magnetic material in one predetermined direction, and a second 
annealing process under a magnetic field having a predetermined direction 
perpendicular to the magnetizable axis, so that the magnetic anisotropy in 
a desired direction is generated by the first annealing process, 
thereafter the magnetic anisotropy thus generated being relaxed by the 
second annealing process, whereby the permeability is increased to improve 
the magnetic characteristics. 
As the magnetic material used in the magnetic head according to the present 
invention, there may be used an amorphous composition and a poly 
crystalline composition containing at least one element selected from the 
iron, nickel and cobalt group, such as iron-nickel alloy, cobalt-niobium 
alloy and cobalt-zirconium alloy as a main composition.

DETAILED DISCUSSION 
It is known that the induced magnetic anisotropy can be induced according 
to the Arrhenius Equation. Expressing the magnetic anisotropy constant by 
K, the equation is expressed as follows: 
EQU K=Ki+[K.sub.O (T)-Ki)]{1-exp(-t/.tau.(T)]} (1) 
wherein 
Ki: initial value; 
K.sub.O (T): constant depending on the absolute temperature and the kinds 
of composition; 
t: time; and 
.tau.(T): relaxation time depending on the absolute temperature. 
.tau.(T) in the equation (1) may be expressed as (2): 
EQU 1/.tau.(T)=A exp(-Ea/kT) (2) 
wherein 
A: constant 
Ea: activation energy 
k: Boltzmann constant 
The term 1/.tau. is referred to as a rate coefficient. 
Accordingly, an annealing process under the magnetic field for a sufficient 
length of time compared to .tau.(T), corresponding to the equation (2), 
enables the magnetic anisotropy to be uniform irrespective of the 
difference of the initial condition of the material. 
The first annealing process of the present invention is employed to enable 
the condition mentioned above. That is, the first annealing process causes 
the initial condition to be uniform so as to suppress the dispersion of 
the magnetic anisotropy after the second annealing process. 
Since the magnetic anisotropy after the first annealing process is 
excessive, there can not be obtained a sufficient high permeability. The 
second annealing process is employed to relax the excessive magnetic 
anisotropy. 
The change of the magnetic anisotropy in terms of time is expressed by the 
equation (3): 
EQU K=K1-[K1+K.sub.O (T')][1-exp(-t/.tau.(T')] (3) 
wherein 
K1: the magnetic anisotropy induced by the first annealing process; 
T': the temperature during the second annealing process and 
K.sub.O (T'): the magnetic anisotropy coefficient when the thermal 
equibillium is reached under the temperature T. 
In order to obtain a sufficiently large permeability, it is necessary to 
make the magnetic anisotropy sufficiently smaller than K1. For this 
purpose, assuming that the processing time of the second annealing process 
is tz, the following equation (4) can be obtained: 
##EQU1## 
If k1 is dispersed in a range.+-..DELTA.K1 with respect to K.sub.10, by an 
annealing process under the condition expressed by the equation (5), 
##EQU2## 
K is dispersed in the range 
##EQU3## 
Accordingly, it is desired to make .DELTA.K.sub.1 as small as possible for 
decreasing the dispersion of the magnetic characteristics. 
As the method decreases .DELTA.K.sub.1 as small as possible, the first 
approach is to keep the condition during the first annealing process 
constant. However, as is apparent from the equation (1), in case the 
initial condition of the composition is dispersed, the value 
.DELTA.K.sub.1 can not be small if only the condition of the first 
annealing process is kept constant. 
In the equation (1), assuming that the value Ki is dispersed in the 
range.+-.K.sub.O, in order for the value K to be present in the range 
expressed by (6) below, then equation (7) must be satisfied. 
EQU K.gtoreq.rK.sub.o (T) (6) 
wherein r is a positive number smaller than 1. 
##EQU4## 
wherein t.sub.1 is annealing process time. 
In order to make r=0.8, equation (8) must be satisfied. 
EQU t.sub.1 /.tau.(T)&gt;Ln 10=2.3 (8) 
By performing the annealing process under such condition mentioned above, 
K.sub.1 is in the dispersion range of +10%. 
In the second annealing process, it is desired to satisfy the equation (5), 
whereby it is necessary to satisfy the condition expressed by the equation 
(9) as K.sub.10 is nearly equal to K.sub.O '. 
##EQU5## 
When the temperature in the first annealing process is substantially equal 
to the temperature in the second annealing process, the equation (10) 
should be satisfied in case the value K.sub.1 is in the range of 0.8 
K.sub.O (T) to 0.9 K.sub.O (T). 
##EQU6## 
The condition mentioned above is made on the premise that the temperature 
of the magnetic material is regulated to the desired value rapidly. 
However, in actuality it is necessary to consider the effect of the 
temperature rising and temperature falling. Accordingly, the optimum 
condition should be decided through various experiments by controlling the 
speeds of either the temperature rising or the temperature falling, 
changing the highest temperature and its holding time. 
As to the condition of the first annealing process, as the magnetic 
anisotropy induced is reached at the saturation value, the dispersion of 
the initial condition against the second annealing process becomes 
decreased. Therefore, it is desired to shorten the annealing time by 
making the annealing temperature as high as possible, decreasing the value 
.tau.(T) within such a range that actual bad effects, such as a change of 
the quality of the magnetic material can be suppressed. 
On the other hand, as to the second annealing process, the optimum 
annealing temperature should be decided so that the holding time of the 
maximum temperature is most suitable in view of making the control easy. 
It is desired that the strength of the applied magnetic field be greater 
than the strength of the demagnetizing field with respect to the applied 
magnetic field for making the difference of the direction of the 
magnetization during annealing from the direction of the applied magnetic 
field as small as possible. 
It is may be possible to replace the first annealing process by the process 
of piling the magnetic layers under the magnetic field in case the 
magnetic path is formed of piled magnetic sheets. 
PREFERRED EMBODIMENTS 
Example 1 
FIG. 3 shows an example of the magnetic head according to the present 
invention. 
In FIG. 3, a substrate 1 of the head core of width W is made of non 
magnetic material, such as Zn-Ferrite. Magnetic thin layers 2 are made so 
as to lay on two opposing surfaces of the substrate 1 forming a head gap, 
the layers 2 being made of an amorphous magnetic alloy (of saturation 
magnetic flux density about 10 KG), cobalt (85% by weight) and zirconium 
(15% by weight). The layers 2 are formed to about 20 .mu.m in thickness by 
way of sputtering. The head core includes head gap regulating thin film 3, 
a coil window 4 for winding an exciting coil (not show) around the 
substrate 1, passing through the window 4 and a glass layer 5. The 
thickness of the magnetic thin layer 2 is selected from 1 to 100 .mu.m in 
order to improve the magnetic characteristics. 
A magnetic head, as shown in FIG. 3, was prepared and write and read 
characteristics with metal powder tape was measured. The magnetic head was 
subjected to an annealing process with magnetic field (annealing in H1) 
under such a condition that the magnetic field coincided with the 
direction W of the width of the head core, subsequently, the magnetic head 
was subjected to another annealing process with magnetic field (annealing 
in H2) under such a state that the direction of the magnetic filed 
coincided with the direction of the depth of the head gap. Each time the 
frequency characteristics were measured. The annealing conditions are as 
follows: 
TABLE 
______________________________________ 
ANNEALING CONDITION IN THE MAGNETIC FIELD 
NO. DIRECTION MAX. TEMP. (.degree.C.) 
TIME (MIN.) 
______________________________________ 
1 H1 330 10 
2 H2 320 10 
3 H1 350 30 
H2 305 10 
4 H1 350 30 
H2 310 10 
5 H1 350 30 
H2 320 10 
6 H1 350 30 
H2 330 10 
7 H1 350 30 
H2 340 10 
______________________________________ 
In the table, direction means the direction of the applied magnetic field 
max. temp. means the applied maximum temperature and time means the 
duration of time during which the maximum temperature was applied. 
In the example, the magnetic field intensity during annealing was about 15 
K oerstead, temperature rising speed and temperature falling speed were 13 
deg/min. in the range higher than 200.degree. C. 
Explaining the table, the sample 1 was a magnetic head without annealing in 
the magnetic field (the magnetic field of the initial condition) which was 
annealed under 330.degree. C. for 10 minutes in the magnetic field of H1 
direction. Sample 2 was a magnetic head same as the magnetic head of the 
sample 1 except that the direction of the magnetic field was H2 and anneal 
was performed at the highest temperature of 320.degree. C. for 10 minutes, 
sample 3 was the same magnetic head as the sample 2 except that the 
magnetic field of H1 was applied first with anneal at 350.degree. C. for 
30 minutes, then subsequently the magnetic field of H2 was applied with 
anneal at 305.degree. C. for 10 minutes, the sample 4 was the same 
magnetic head as the sample 3 except that the magnetic field of H1 was 
further applied with anneal at 350.degree. C. for 30 minutes subsequently 
the magnetic field of H2 was applied with anneal at 310.degree. C. for 10 
minutes. As mentioned above, all of the samples are subjected to the 
magnetic fields of H1 and H2 and anneal repeatedly. 
Test was made using three samples for each groups of 1 to 7. Result of the 
tests are shown in FIG. 4 in which o, x and .DELTA. represent the 
respective characteristic value. Distance between the respective marks o, 
x and .DELTA. represents the dispersion of the respective samples of the 
magnetic heads and the long distance represents a large dispersion of the 
products and the short distance between the marks represents a small 
dispersion of the products. 
From the test it is understood that the samples No. 2 to No. 7 have high 
relative outputs, particularly the samples 4, 5 and 6 all have high 
outputs with small dispersion. 
The anneal process for the magnetic head of the sample 2 in terms of the 
second magnetic process H2 was the same as the anneal process for the 
sample 5. However, in the sample 2, since the maximum temperature of the 
first annealing condition of the sample 2 which corresponds to the 
annealing condition for the sample 1 is lower than the condition for the 
sample 5, it can be noticed that the induced anisotropy of the sample 2 
did not reach the saturation and the dispersion of the product is 
remarkable. 
As to the magnetic head of the sample 3, since the maximum temperature of 
the second annealing with the magnetic field H2 is slightly low, a 
sufficient characteristic can not be obtained. 
As to the magnetic head of the sample 7, since the maximum temperature of 
the second annealing with the magnetic field H2 is excessively high, the 
relative output is decreased. 
Compared with the above samples, the magnetic heads of the samples 4, 5 and 
6 have high outputs with small dispersion of the products since the 
temperatures of both first and second anneal with the magnetic fields H1 
and H2 are suitable. 
In the example mentioned above, the respective directions of the applied 
field in the first and second annealing processes with the magnetic field 
may be replaced. It has been noticed that replacement of the direction of 
the magnetic field mentioned above has never badly affected to the various 
effects mentioned above. 
Principally, the direction of the applied magnetic fields may be 
perpendicular each other for obtaining good effects. In case the portions 
of the head made of the magnetic material are shaped with a symmetry, with 
the symmetric axis thereof selected as one of the directions of the 
applied magnetic field, it is easy to orient the magnetization direction 
in the magnetic material with the direction of the applied magnetic field 
uniformly, therefore it is possible to obtain the effect of the annealing 
processing uniformly everywhere and specific control of the magnetization 
is also possible. 
In view of the technical meaning mentioned above, in the thin film head, it 
is possible to select the direction perpendicular to the surface of the 
magnetic film as one of the directions of the applied magnetic field. 
However, in this case the counter magnetic field is strong, thus it is 
necessary to make the applied magnetic field strong. 
Example 2 
A plurality of the magnetic heads having the shape as shown in FIG. 3 were 
prepared, and were subjected to the first anneal process with magnetic 
field of H2 with 15 K oerstead and at the maximum temperature 350.degree. 
C. for 30 minutes keeping the maximum temperature. Subsequently, the 
magnetic heads were subjected to the second anneal process with magnetic 
field of H1 with 15 K oerstead at the maximum temperature 320.degree. C. 
for 10 minutes keeping the maximum temperature. After those annealing, the 
magnetic head has a low dispersion with the outputs of 1.4 to 1.6 times of 
those of the magnetic heads without annealing. 
Example 3 
As the first annealing with the magnetic field, it may be preferred to 
anneal the magnetic head already assemble in the shape of the magnetic 
head as shown in FIG. 3, it may be possible to anneal applying the 
magnetic fields in the predetermined direction at the time of sputtering 
of the thin magnetic thin layer 2 on the substrate during the 
manufacturing of the magnetic heads. 
Example 3 is directed to the method mentioned above. 
The magnetic thin film 2 was formed on the substrate made of Zn-ferrite 
using amorphous magnetic alloy of cobalt (85% by weight)-zirconium (15% by 
weight) under the following sputtering condition; 
(1) diameter of the target 203 mm 
(2) vacuum 5.times.10.sup.-3 torr with argon 
(3) radio frequency of 800 Watts 
(4) sputtering rate of 3 .mu.m/hour. 
In this case, the magnetic thin layer was bonded on the substrate under the 
magnetic field of about 100 oerstead in the direction corresponding to the 
direction H1 of the widthwise direction of the head core of the magnetic 
head. 
The parts of the substrate thus obtained were assembled to form the 
magnetic head, thereafter the magnetic field was applied in the direction 
H2 and the second annealing was processed at the maximum temperature 
320.degree. C. for 10 minutes keeping the maximum temperature. The 
dispersion of the magnetic heads thus annealed were few with high output 
1.4 to 1.6 times compared to the magnetic head without the annealing 
process. 
Example 4 
The annealing process according to the present invention is also effective 
to obtain a good effect in case of using poly crystalline magnetic alloy 
such as Sendust magnetic alloy, Permalloy magnetic alloy (NI 78-80% by 
weight-Mo 0-2% by weight-Fe 17-20% by weight) or Fe 84% by weight - Al 16% 
by weight alloy, Fe 49% by weight-Co 49% by weight - Ru 2% by weight 
alloy. Magnetic head using Sendust (Fe 85% by weight - Si 9.6% by weight - 
Al 5.4% by weight) as the magnetic thin layer were prepared under the same 
condition of the sample 5. The magnetic thin layer made of Sendust was 
formed under the same sputtering condition as used in the example 2. The 
magnetic heads thus obtained have high output of 1.4 to 1.6 times of the 
output of the magnetic head without annealing according to the present 
invention. 
As mentioned above, the first annealing with the magnetic field of the 
present invention enables the inducement of a relatively large amount of 
anisotropy in the magnetic portion of the magnetic head and the second 
annealing with the magnetic field enables the relaxing of the anisotropy 
so as to make the permeability large, whereby good magnetic 
characteristics for the magnetic head can be obtained with a simple 
apparatus and simple processing. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the present invention, and all such 
modifications as would be obvious to one skilled in the art are intended 
to be included within the scope of the following claims.