Magnetic head containing amorphous alloy and crystallizable glass

The present invention relates to a magnetic head in which a magnetic metal film comprising a Co-containing amorphous alloy and a crystallizable glass of the PbO-B.sub.2 O.sub.3 -ZnO system as a solder glass are used. The magnetic head of the present invention has about 2 times higher recording density than the conventional one as a magnetic head for floppy disks and hard disks because an amorphous alloy is used. Since a crystallizable glass is used as the glass, there can be obtained a magnetic head having a high strength and superior humidity resistance and reliability.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic head in which a magnetic metal 
film comprising a Co-containing amorphous alloy and a crystallizable glass 
of the PbO-B.sub.2 O.sub.3 -ZnO system as a solder glass are used. 
2. Description of the Prior Art 
In recent years, floppy disk devices and hard disk devices used as an 
external memory of various computers have been advanced whereby such 
devices have become small and have obtained a high recording density. 
Therefore, a magnetic head, which can be viewed as the heart of the disk 
device, is also required to have a high performance, and hence a magnetic 
head has been developed in which a magnetic amorphous metal film (Co-Nb-Zr 
alloy) having a saturated magnetic density of high volume is used. 
These magnetic heads are mainly formed with a head core, which is made of a 
magnetic material, and a ceramic slider, which is made of a non-magnetic 
material, by a joining technique with glass. 
The joining process contains two steps which comprise a step wherein, after 
filling of glass to a magnetic head core, gaps of the head cores are 
joined to each other by glass, and a step wherein a head chip cut off from 
the head core are joined to a ceramic slider by glass. 
In this case, the magnetic core is filled with glass at a temperature of 
about 420.degree. C. (but 420.degree. C. or below) and once the 
temperature is lowered naturally. Thereafter, the gaps of the head cores 
are joined to each other by glass at a temperature of 450.degree. C. 
Furthermore, the head chip cut off from the head core is joined to the 
ceramic slider at a temperature of from exceeding 450.degree. C. up to 
460.degree. C. by glass. 
In this case, the magnetic amorphous metal film is crystallized when heated 
to the temperature of higher than 500.degree. C., resulting in extreme 
deterioration of magnetic properties. Therefore, it is important to select 
the glass which is workable at a temperature of 500.degree. C. or less and 
has a thermal expansion coefficient as near as possible to those of the 
head core and the ceramic slider in order that the magnetic head may not 
crack due to the difference of the thermal expansion caused by the 
temperature change in the construction procedures. 
When an amorphous glass is used as the solder glass (abbreviated as glass 
A) for joining the gaps of the head cores, it is necessary to select a 
solder glass (abbreviated as glass B) for joining the head chip to the 
ceramic slider such that a glass B enables joining at a temperature lower 
than the softening temperature of glass A so that size distortion may not 
occur. 
Thus, the softening temperatures of glass A and glass B must differ 
greatly. Moreover, a glass having a low softening temperature has a large 
thermal expansion coefficient and hence, the selection of glass is not 
easy. 
On the other hand, though an adhesive such as an epoxy resin or the like is 
effective because it is workable at 300.degree. C. or below and hence the 
magnetic amorphous metal film is not influenced, it is difficult to 
maintain very precise gaps thereby. 
Under these circumstances, use of a crystallizable glass has been 
investigated as the glass A, and the glass is improved in thermal 
resistance by crystallization, whereby the working temperature of the 
glass B is elevated. That is, it is desired that the glass A has an 
elevated melting temperature when it is crystallized. 
Thus, even if the working temperature of glass B is raised to the working 
temperature of glass A, the glass A which has been crystallized once is 
not melted at the initial working temperature, so that the glass A itself 
can be used as the glass B. 
Further, an amorphous glass may of course be used as the glass B. In this 
case, it is preferable to select and use those fit for the thermal 
expansion coefficient of the glass A. 
The joining of gaps of the head cores comprises bringing two cores in which 
their head core grooves have been filled with glass face to face and 
heating them to join them. 
In the glass filling operation, it is impossible to join the cores when the 
glass is crystallized. Therefore, it is necessary to select as the glass A 
a crystallizable glass having characteristics such that it is not 
crystallized during the above-mentioned glass filling while it is 
crystallized at the core joining time. 
Japanese Patent Application Kokai (Laid-Open) No. 20265/1980 discloses a 
sealing glass consisting of: 
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PbO 77.about.86 wt % 
ZnO 7.about.12 wt % 
B.sub.2 O.sub.3 
7.about.11 wt % 
SiO.sub.2 
1.about.3 wt % 
______________________________________ 
However, this glass composition is crystallized during the above-mentioned 
filling operation. Due to the crystallization, it is necessary to raise 
the working temperature for joining in the subsequent joining step higher 
than normally required. This is not preferable for joining the gaps of the 
magnetic head. 
SUMMARY OF THE INVENTION 
The present invention is to provide a magnetic head in which a head part is 
fixed to a ceramic slider, the head part being formed by bringing a pair 
of magnetic cores face to face so that a magnetic gap may appear on the 
face confronting a magnetic recording medium, the place where the pair of 
magnetic cores are brought face to face is constituted by magnetic metal 
films joined to each other via a solder glass layer to form a gap, 
said magnetic metal film comprising a Co-containing amorphous alloy, and 
said solder glass comprising a crystallizable glass in PbO-B.sub.2 O.sub.3 
-ZnO system having the following composition: 
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PbO 75.about.85 wt %, 
ZnO 5.about.10 wt %, 
B.sub.2 O.sub.3 
7.about.12 wt %, 
SiO.sub.2 0.5.about.2.0 wt %, 
K.sub.2 O 0.5.about.1.0 wt %, 
CuO 0.5.about.2.0 wt %, 
______________________________________ 
The magnetic Co-containing amorphous metal film is deteriorated in magnetic 
properties when crystallized. The crystallizing temperature is about 
550.degree. C. 
The joining of the gaps of the magnetic cores and the joining of the head 
chip cut off from the magnetic core to the non-magnetic ceramic slider 
must be carried out at a working temperature of about 460.degree. C. or 
below with all reserve. 
An object of the present invention is to provide a glass composition having 
characteristics such that the working temperature is 460.degree. C. or 
below, and it is hardly crystallized in the filling operation of glass to 
the grooves of the magnetic core, while it is crystallized when two 
magnetic cores filled with glass are joined. 
The glass of the present invention is a low temperature softening 
crystallizable glass composed mainly of PbO and having a viscosity of 
10.sup.4 poise or below at 460.degree. C. (corresponding to the working 
point of glass). Concrete composition of the glass comprises the following 
main constituents: 
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PbO 75.about.85 wt % 
ZnO 5.about.10 wt % 
B.sub.2 O.sub.3 
7.about.12 wt % 
SiO.sub.2 0.5.about.2.0 wt % 
K.sub.2 O 0.5.about.1.0 wt % 
CuO 0.5.about.2.0 wt % 
______________________________________ 
The glass having a composition in the above-mentioned ranges has a 
transition point in the range of 280.degree. C. to 300.degree. C., a point 
of incipient deformation in the range of 300.degree. C. to 320.degree. C., 
a softening point in the range of 360.degree. C. to 380.degree. C., a 
crystallization initiating temperature (corresponding to the temperature 
of joining operation) in the range of 450.degree. C. to 470.degree. C. and 
a thermal expansion coefficient of glass after crystalization of 
90.about.110.times.10.sup.-7 /.degree.C. 
The glass of the present invention is extremely preferable for joining a 
magnetic head, particularly a magnetic head in which a magnetic amorphous 
metal film is used. 
The joining of gaps of the magnetic cores comprises two steps, one of which 
is a filling operation of glass to a magnetic core and the other is a step 
wherein two magnetic cores filled with glass are brought face to face and 
joined. It is necessary to carry out the glass filling operation at a 
temperature not higher than the crystallization initiating temperature 
because the magnetic cores can not be joined if the filled glass is 
crystallized. However, if the filling temperature is too low, the fluidity 
of the glass deteriorates, resulting in unsatisfactory wetting of glass to 
the adherent. Therefore, it is necessary to set the temperature for the 
glass filling operation between the temperature at which glass begins to 
flow (commonly called the flow point) and the crystallization initiating 
temperature. Furthermore, in the glass filling operation, it is necessary 
to maintain the step temperature for at least 10 to 30 minutes for wetting 
the adherent with glass. 
The crystallization initiating temperature of glass of 450.degree. C. to 
460.degree. C. mentioned in the present invention is a value obtained when 
the glass is heated at a rate of 5.degree. C./minutes, while the 
crystallization is caused even at the temperature of 450.degree. C. or 
below if it is maintained for a time longer than a fixed time. 
FIG. 1 is a graph showing the relation of temperature to crystallization 
state, and the retention time is 30 minutes. The length of crystallization 
development of the ordinate axis is a value obtained by observation of 
total length of crystallization construction developing inside from the 
glass surface by a light microscope. 
As clear from the drawing, in glass .circle.b composed of PbO-ZnO-B.sub.2 
O.sub.3 -SiO.sub.2, crystal has been developed up to about 200.mu. from 
the glass surface when it has been maintained at 420.degree. C. for 30 
minutes. On the contrary, in the glass .circle.a of the present 
invention, crystallization is not caused even when the glass is maintained 
at 430.degree. C. for 30 minutes. 
The above-mentioned glass .circle.b has a softening point of 370.degree. 
C. and a crystallization initiating temperature (characteristics obtained 
when heated at a rate of 5.degree. C./minutes) of 430.degree. C., the 
softening point being the same as that of the glass .circle.a of the 
present invention while the crystallization initiating temperature is 
about 40.degree. C. lower than that of the glass .circle.a of the 
present invention. 
The glass of the present invention can be prepared by mixing raw glass 
materials, putting them in an alumina or platinum crucible, heating and 
melting them in an electric furnace at 950.degree. C. to 1000.degree. C. 
for one hour, casting them in a graphite jig (preheating temperature: 
150.degree. C. to 200.degree. C.) and cooling them by leaving. 
The reason why the compounding proportion of the glass composition of the 
present invention is limited to that mentioned above is as follows. 
Although PbO lowers the softening point of the glass and brings good 
fluidity thereto, the fluidity deteriorates if it is less than 75% by 
weight, while the thermal expansion coefficient becomes high if it exceeds 
80% by weight. 
ZnO contributes to crystallization of glass. Nevertheless, if it is less 
than 5% by weight, the glass can not be crystallized at a working 
temperature of 450.degree. C., while if it exceeds 10% by weight, the 
glass can not be put to practical use because of excess crystallization. 
B.sub.2 O.sub.3 is a glass forming oxide. If it is less than 7% by weight, 
vitrification of the composition can not be accomplished, while if it 
exceeds 12% by weight, the fluidity of glass deteriorates and 
crystallization is imperfect, so that the glass can not be put to 
practical use. 
SiO.sub.2 is also a crystallization adjustor. If it is less than 0.5% by 
weight, it is not effective, while if it exceeds 2% by weight, the glass 
is hardly crystallized. 
K.sub.2 O improves the fluidity of the glass. However, if it is less than 
0.5% by weight, it is not effective, while if it exceeds 2% by weight, the 
glass is hardly crystallized and the water resistance of the glass 
deteriorates. 
CuO also improves the fluidity of the glass and is effective for making 
crystals minute. Nevertheless, if it is less than 0.5% by weight, it is 
not effective, while if it exceeds 2% by weight, the softening point 
becomes high and Cu is crystallized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is described referring to the following Examples. 
EXAMPLE 1 
Compositions and physical properties of the glass used in the present 
invention are shown in Table 1. 
With regard to the measurement of the physical properties, the softening 
point and crystallization initiating temperature are measured by using 
powdered glass by means of an apparatus for differential thermal analysis 
at a heating rate of 5.degree. C./minute. 
The thermal expansion coefficient is measured by usind a test piece 
obtained by cutting a glass having been crystallized in a size of 
5.phi..times.20 mm by means of a thermal expansion measuring device. 
TABLE 1 
______________________________________ 
Conven- 
tional 
.circle.1 
.circle.2 
.circle.3 
.circle.4 
glass 
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PbO 78 80 84.5 80 80 
ZnO 8 8.5 4.5 9 9 
B.sub.2 O.sub.3 
12 8 7.5 8 9 
SiO.sub.2 
1.0 2.0 1.0 1.0 2 
K.sub.2 O 
1.0 0.5 0.5 0.5 0 
CuO 0.5 1.0 2.0 1.5 0 
Softening 
375 370 365 373 370 
temperature 
(.degree.C.) 
Crystal- 470 460 450 456 420 
lization 
initiating 
temperature 
(.degree.C.) 
Thermal 93 102 110 100 100 
expansion 
coefficient.sup.(1) 
(.times. 10.sup.-7 /.degree.C.) 
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.sup.(1) Thermal expansion coefficient after crystallization. 
The glass can be filled without crystallization. Furthermore, the joining 
operation after the glass filling operation can easily be conducted by 
heating at the crystallization initiating temperature. The thermal 
expansion coefficient after crystallization is 93-110.times.10.sup.-7 
/.degree.C. which is fit for the thermal expansion coefficient of a 
magnetic head (magnetic core: 110.times.10.sup.-7 /.degree.C.) and ceramic 
slider (108.times.10.sup.-7 /.degree.C.). 
EXAMPLE 2 
A process for producing a composite type magnetic head using glass 
.circle.2 in Table 1 is shown in FIG. 2. 
A magnetic amorphous metal film (Co-Nb-Zr alloy, thickness of film: 25.mu.) 
3 and SiO.sub.2 (thickness of film: 1.mu.) 4 are formed on the surfaces of 
a C-shaped magnetic core and a I-shaped magnetic core which have W-shaped 
grooves by a sputter method (FIG. 2(b)). The magnetic amorphous metal film 
mentioned herein is decreased in vortex current loss of the magnetic film 
by laminating magnetic amorphous metal films (thickness of film: 5.mu.) 5 
and SiO.sub.2 films (thickness of film: 0.05.mu.) 6 one after another as 
shown in FIG. 2(c). The magnetic film is a laminate having five layers. 
Subsequently, a low temperature softening crystallizable glass (size: 
4.times.15.times.0.5 t) 7 having a weight proportion of 80% PbO-8.5% 
ZnO-2% SiO.sub.2 -0.5% K.sub.2 O-1.0% CuO is put on the surface of the 
core having the magnetic amorphous metal layer 3 and the SiO.sub.2 film 4 
formed thereon (FIG. 2(d)), and heated to 430.degree. C. for 30 minutes, 
thereby the W-shaped grooves are filled with the glass 7. At this time, 
the glass 7 is not crystallized yet. 
After filling of the glass, the upper surface of the W-shaped grooves is 
ground to make tracks (FIG. 2 (f)). The track size is about 10.mu.. After 
determination of the track size l, a SiO.sub.2 film (thickness of film: 
0.1.mu.) 8 for regulating the gap size is formed on the upper surface of 
the W-shaped grooves by sputter method (FIG. 2(g)). 
The magnetic cores 1 and 2 having a gap size regulating SiO.sub.2 film 
formed thereon are joined to each other by bringing their W-shaped groove 
portions face to face and heating them at 450.degree. C. for 30 minutes 
(FIG. 2(h)). At this time, the glass 9 is crystallized. After joining by 
glass, the magnetic core 10 is cut (FIG. 2(i)) to obtain magnetic core 
chips (FIG. 2(j)). 
The obtained magnetic core chip is inserted into a slot 13 of a 
non-magnetic ceramic slider (CaTiO.sub.3) 12 (FIG. 2(k)) and a glass 
(size: .phi.0.5.times.15 l) of the same kind as 7 is put on the space 14 
between the magnetic core chip and the non-magnetic ceramic slider 12 and 
heated at 430.degree. C. for 30 minutes to join the magnetic core chip to 
the non-magnetic ceramic slider (FIG. 2(l)). After joining by glass, a 
composite type magnetic head 16 is completed by lapping (FIG. 2(m)). 
EFFECT OF THE INVENTION 
The magnetic head of the present invention has about 2 times higher 
recording density than the conventional one as a magnetic head for floppy 
disk or hard disk because an amorphous alloy is used. 
Since a crystallizable glass is used as the glass, there can be obtained a 
magnetic head having a high strength and superior humidity resistance and 
reliability. 
Further, the glass of the present invention is a low temperature softening 
crystallizable glass suitable for a solder glass for a magnetic head with 
high performance for floppy disk and hard disk in which a magnetic 
amorphous film is utilized and two joining steps are required. Therefore, 
filling of glass to a magnetic core is made possible without 
crystallization of glass at a temperature of 430.degree. C. Moreover, 
crystals are micronized by addition of CuO, so that the glass is excellent 
in resistance to wear.