[0001] The present invention relates to an amorphous alloy which is used as a core material
for a magnetic head, and a magnetic head with an amorphous alloy.
[0002] In magnetic heads conventionally used for magnetic recorders/reproducers, a highly
magnetic permeable material having a crystalline structure is employed, such as an
Fe-Ni alloy (Permalloy) or an Fe-Si-AA alloy (Sendust). However, the Fe-Ni alloy has
a disadvantage, in that its wear resistance is low; and, although the Fe-Si-At alloy
has good wear resistance, it also has disadvantages, in that its mechanical strength,
brittleness and plastic processing capacity is low.
[0003] The amorphous alloy having no crystalline structure, such as a Co-Fe-Ni-Si-B alloy,
has recently been identified as an ideal material for a magnetic head. Such amorphous
alloys have excellent magnetic properties, such as high saturation magnetization and
low magnetostriction, along with high mechanical strength, good wear resistance and
good processing capacity.
[0004] However; in general, the magnetic head used for a VTR (video tape recorder) must
be stably and rigidly. Therefore, especially, the core halves of the magnetic head
of a VTR are normally secured each other with a glass adhesive to form the gap. The
glass bonding process involved requires heat treatment at a temperature higher than
400°C, and a gradual cooling after heat treatment. However, the amorphous alloys all
have their respective crystallization temperatures; and the magnetic properties and,
particularly, the effective magnetic permeability of the amorphous alloy are deteriorated
by heat treatment at a temperature in the vicinity of the crystallization temperature.
Further, the conventional low magnetostriction amorphous alloys contain at least two
or more of the magnetic elements comprised of Co, Fe and Ni. Consequently, an induction
magnetic anisotropy is produced by the heat treatment, and the magnetic properties
of the amorphous alloys are thereby deteriorated. Thus, the conventional amorphous
alloys have disadvantages, in that the practicability of using them for the magnetic
head of a VTR is low.
[0005] Thus, there is a present need for an amorphous alloy whose magnetic properties do
not deteriorate after glass bonding; i.e., for an amorphous alloy which has a crystallization
temperature higher than the temperature necessary for a glass bonding heat treatment
(i.e., higher than 500°C), whose magnetic properties do not deteriorate, even with
the gradual cooling which occurs after heat treatment. If only one of the magnetic
elements is contained in the amorphous alloy, the deterioration, after gradual cooling,
of the effective magnetic permeability of an amorphous alloy having this composition
can be prevented. However, such an amorphous alloy has certain disadvantages, in that
the requirements for high saturation magnetization and low magnetostriction cannot
be satisfied.
[0006] As described above, a magnetic head with an amorphous alloy bonded by a glass adhesive
is not yet provided, which magnetic head has high saturation magnetization and low
magnetostriction and maintainsa high level of effective magnetic permeability.
[0007] A primary object of the present invention is to provide an amorphous alloy for a
magnetic head, which alloy has excellent magnetic properties, such as high saturation
magnetization and low magnetostriction.
[0008] Another object of'the present invention is to provide an amorphous alloy for a magnetic
head, which alloy has a crystallization temperature higher than 500°C and undergoes
no deterioration of its magnetic properties, such as its effective magnetic permeability,
even in a heat treatment combined with a gradual cooling.
[0009] Still another object of the present invention is to provide a magnetic head which
exhibits excellent magnetic properties, without lowering its effective magnetic permeability,
even if a core composed of an amorphous alloy having high saturation magnetization
and low magnetostriction is subjected to a glass bonding heat treatment.
[0011] This invention can be more fully understood from the following detailed description
when taken in conjunction with the accompanying drawing, in which:
[0012] The figure is a graph showing the effect of a Co-Re-Hf-B alloy on saturation magnetization,
in cases where Co is substituted for Re.
[0014] The reasons for requiring the above respective elements and the reasons for limiting
the composition of the alloy,-as above, may be explained in greater detail, with reference
to the present invention.
[0015] An amorphous alloy according to the present invention mainly comprises a cobalt (Co).
Among such alloys, an amorphous alloy having a saturation magnetization higher than
0,8 T (8 kGauss) and low magnetostriction (λ
s) (| λs | ≦ 10
-6) can be readily obtained.
[0016] M (Ni or Re) is contained in the amorphous alloy because the nickel (Ni) or rhenium
(Re) serves to raise the crystallization temperature of the alloy and lower the magnetostriction.
The atomic density T of the Ni or Re is so set as to satisfy the above formula (1);
since, if the atomic density T is lower than 0.2 and higher than 14, the adding effect
of the Ni or Re cannot be readily obtained.
[0017] It is preferable to set the atomic density T of the Ni within a range of from 0.75
to 14, when the Ni is contained in the amorphous alloy. The Ni has the effect of enhancing
the crystallization temperature and also increasing the magnetic permeability of the
amorphous alloy. In this case, the effect of enhancing the magnetic permeability can
be preferably obtained within the above range of atomic density.
[0018] It is preferable to set the atomic density T of the Re within a range of from 0.2
to 6, when the Re is contained in the amorphous alloy. The Re has the effect of lowering
the saturation magnetostriction constant of the alloy, with the addition of small
amounts. When this effect is substantial, the saturation magnetostriction constant
might become a negative value, with the addition of the Re. The atomic density T of
the Re is set at a level higher than 0.2; since, if the Re is lower than 0.2, the
effect whereby the saturation magnetostriction constant is lowered by the addition
of the Re is lessened. The atomic density T of the Re is set lower than 6; since,
if the Re is more than 6, the saturation magnetization of the alloy, by the addition
of the Re, is reduced.
[0019] On the other hand, the Re has the effect of raising the saturation magnetization
level of the alloy. The figure shows the variation in the saturation magnetization
level which occurs in cases wherein the atomic density T of the Re is altered in the
alloy Co
78.5-TRe
THf
11.5B
10.0, i.e., the saturation magnetization effect which occurs in cases wherein the Co is
substituted for the Re. As is evident from the Figure, the saturation magnetization
level of the alloy can be raised by setting the atomic density T of the Re within
a range of from 0.2 to 1.5. Therefore, an amorphous alloy which has a high crystallization
temperature, a low saturation magnetostriction constant and a high saturation magnetization
level may be provided, by setting the atomic density T of the Re within a range of
from 0.2 to 1.5.
[0020] The hafnium (Hf) is contained in the amorphous alloy according to the present invention
because the Hf has the effect of raising the crystallization temperature of the alloy.
The atomic density X of Hf is so set as to satisfy the above formula (2); since, if
the X is lower than 6, a crystallization temperature higher than 500°C cannot be obtained
and, similarly, if the X is higher than 15, a crystallization temperature higher than
500°C cannot be obtained and it will be difficult to raise the saturation magnetization
level of the alloy above 0,8 T (8 kGauss).
[0021] The boron (B) is contained in the amorphous alloy of the invention because the B
has the effect of aiding in the formation of the amorphous alloy and improving the
physical properties of the alloy. The atomic density Y of the B is so set as to satisfy
the above formula (3); since, if the Y is lower than 3, the effect of aiding in the
formation of the amorphous alloy with the B is lessened and, if the Y is higher than
14, the rust resistance of the alloy deteriorates and brittleness is produced. It
is preferable to set the atomic density Y of the B lower than 8; since, if the atomic
density Y of the B is less than 8, the production of the amorphous alloy is facilitated
and its wear resistance can be improved.
[0022] Further, it is preferable to set the X and Y at such a level as to satisfy the following
inequality (7), when the alloy contains the Re.

If the X/(X+Y) factor is lower than 0.5, the effect whereby the magnitude of the saturation
magnetostriction is reduced by the addition of the Re cannot be obtained. If the X/(X+Y)
factor is higher than 5/6, the formation of an amorphous alloy becomes difficult,
and an amorphous alloy having high saturation magnetization cannot be obtained.
[0023] The addition of the silicon (Si) is effective in aiding the formation of the amorphous
alloy. In this case, the atomic density Z of the Si is so set as to satisfy the above
formula (4). The formation of the amorphous alloy can be performed by including another
element, such as B, even if the Si is not contained in the alloy. Further, the atomic
density Z of the Si is so set as to be lower than 11; since, if it is higher than
11, the effect of forming the amorphous alloy by the addition of the Si is lessened.
[0024] To obtain an amorphous alloy which has high saturation magnetic flux density and
high coercive force; and, yet, does not have its effective magnetic permeability lowered,
said amorphous alloy should not contain the Si. However, when the atomic density Z
of the Si is set within a range of from 0 to 0.01, an alloy can be obtained which
has magnetic properties substantially similar to an alloy having no Si. Therefore,
it is preferable to set the atomic density Z of the Si within a range of from 0 to
0.01.
[0025] The atomic densities X, Y, Z of the Hf, B and Si are so set as to satisfy the above
formulae (5), (6). If the total addition amount of the B and Si is lower than 3 at
atomic density Y+Z, the formation of the amorphous alloy is rendered difficult; and,
if higher than 13, an alloy having a magnetic permeability higher than 5,000 (in 1
kHz) cannot be obtained. When the total addition amount of the Hf, B and Si is lower
than 11 at atomic density X+Y+Z, the crystallization temperature of the alloy is decreased
to a level lower than 500°C; and, when higher than 25, the saturation magnetic flux
density is decreased to a level lower than 0,7 T (7 kGauss),
'with the result that an actual problem occurs in the material used for the magnetic
head.
[0026] The amorphous alloy which contains the composition described above is produced by
the steps of preparing powders of Co, Ni (or Re), Hf, B and Si (as required) at a
predetermined ratio, melting them, and forming the molten metals into an amorphous
alloy by e.g., a liquid quenching method or a sputtering method. In this case, the
amorphous alloy may be heat treated, as required.
[0027] A magnetic head can be produced from the core material which is obtained by machining
the amorphous alloy in a predetermined shape. A rotary magnetic head device for a
VTR can be constructed by mounting the magnetic head on a rotor; or, a rotary magnetic
head device might also be constructed by a thin film forming technique, by directly
forming a core at a rotor and further forming a coil pattern.
[0028] The amorphous alloy according to the present invention has a crystallization temperature
level higher than 500°C and does sustain no decrease in its effective magnetic permeability,
even if a heat treatment process with the gradual cooling needed for glass bonding
is carried out to make a head tip. Therefore, a magnetic head which has excellent
electromagnetic conversion properties, and magnetic properties such as a high saturation
magnetization level, a low magnetostriction level, high effective magnetic permeability,
high mechanical strength and high wear resistance can be obtained by fabricating the
head from the amorphous alloy of the present invention.
[0029] Some examples of the invention may be described as follows, in conjunction with comparative
examples. In Table 1, Examples 1 to 4 and Comparative Examples 1 to 6 of the Ni-series
amorphous alloy are listed. In Table 2, Examples 5 to 7 and Comparative Examples 7
to 11 of the Re-series amorphous alloy are listed.

[0030] Amorphous alloys of the compositions listed in Tables 1 and 2 were respectively prepared
by a liquid quenching method. More particularly, thin.strip specimens of an amorphous
alloy, which were 30 µm thick and 12 mm wide, were produced by injecting the molten
alloys of the above compositions on the surface of a sole roll rotating at a high
rate of speed in an argon gas atmsphere through argon gas under pressure (0,098 -
0,98 bar (0.1 - 1.0 kg/cm
2))from the nozzle of a quartz tube; and by then quenching the alloys. The specimens
in Comparative Example 1 contained no Hf; the specimens in Comparative Example 2 contained
B and Si, so that the total amount Y+Z of the atomic densities of the B and Si exceeded
13; Comparative Example 3 contained Hf, B and Si, so that the total amount X+Y+Z of
the atomic densities exceeded 25; Comparative Example 4 contained Hf but no Ni; and
Comparative Example 5 contained Hf, so that the atomic density X of the Hf exceeded
15.
[0031] Comparative Example 6 employed an Mn-Zn ferrite of the head material which is currently
used in domestic VTRs. General data, excepting the crystallization temperatures, was
listed in Table 1.
[0032] Comparative Example 7 contained less than half the ratio X/(X+Y) of the Hf to the
sum of the Hf and the B, Comparative Example 8 contained Hf in such an amount that
the atomic density Y of the Hf exceeded 15, Comparative Example 9 contained no Re,
Comparative Example 10 contained Nb (instead of the Re), and Comparative Example 11
contained no Re and no Hf.
[0033] The following properties were measured, as below, for the thin strip specimens. General
data, excepting the crystallization temperature, for the Comparative Example 6 were
also measured.
(i) Crystallization Temperature
[0034] The crystallization temperatures were measured by a differential thermal analyzer,
in such a manner that the temperatures were determined by the heat starting temperature
of the heating peak initially presented during the period of temperature rise.
(ii) Saturation Magnetization
[0035] Saturation Magnetization was determined by measuring the values of the magnetization
of the respective specimens, in a magnetic field of 0,8 MAm
-1 (10 kOe), with a specimen vibration type magnetization measuring instrument.
(iii) Effective Magnetic Permeability
[0036] The thin strip specimens were punched in a ring shape, having a 10 mm outer diameter
and an 8 mm inner diameter, and ten sheets of the specimens were laminated via interlayer
insulators, i.e. sputtered films of soda glass having a softening point of 380°C.
Then, after the laminate was heat treated at 500°C to 530°C for 30 min., it was gradually
cooled at a rate of 3°C per minute, and laminated cores were obtained. The laminated
cores of the amorphous alloy were respectively wound with 30 turns of primary and
secondary coils, the inductances were measured by an impedance meter, and the effective
magnetic permeability
pi levels were obtained by calculation. The effective magnetic permeabilities were at
the 500 kHz and 5 MHz levels for the Re-series amorphous alloy and at the 5 MHz levels
for the Ni-series amorphous alloy.
(iv) Coercive Force and
[0037] Saturation Magnetic Flux Density
[0038] The coercive forces and saturation magnetic flux densities were obtained by using
specimens similar to those used in measuring the effective magnetic permeability,
and by obtaining a DC magnetization curve with an automatic self-recording magnetic
flux meter and calculating the coercive force from this curve.
(v) Saturation Magnetostriction Constant
[0039] The saturation magnetostriction constants were measured by a strain gauge method.
(vi) Wear Amount
[0040] The thin amorphous alloy strip specimens were respectively cut to form magnetic head
cores for a VTR, and the wear resistances of the heads were measured. Wear resistance
was evaluated by observing the tape sliding surface of the magnetic head before and
after a VTR cassette tape coated with y-Fe
20
3 was fed on the magnetic head for 500 hours, from the side surface by an optical microscope;
and thereby obtaining wear amounts converted to that per 100 hours.
[0041] The compositions of the specimens and the measured values of magnetic properties
were listed in Tables 1 and 2.
[0042] As may be seen from Table 1, the crystallization temperatures of the amorphous alloys
of Examples 1 to 4 were confirmed to be higher, by approx. 300°C, than those of the
amorphous alloy containing no Hf. In addition, the magnetic properties and, particularly,
the effective magnetic permeabilities µ ' (5 MHz) of the specimens heat treated with
gradual cooling of Examples 1 to 4 were not deteriorated, as compared to those of
the Comparative Examples 1 to 5.
[0043] It was also confirmed that, when the amount of Si added approached 0, the saturation
magnetic flux density had increased and the deterioration of the effective magnetic
permeability, which is due to the gradual cooling, was not observed. In addition,
it was also confirmed that the wear resistance was substantially improved due to the
reduction of the amount of B added.
[0044] As may readily be seen from Table 2, in Comparative Example 7, the saturation magnetostriction
constant is of a large value, since ratio X/(X+Y) is less than 0.5; and Comparative
Example 8 has an extremely small saturation magnetization value, since the atomic
density of the Hf exceeds 15. Further, Comparative EXamples 9 and 10 have remarkably
large saturation magnetostriction constants, since Comparative Example 9 contained
no Re and Comparative Example 10 contained Nb (instead of the Re). In addition, though
the amorphous alloy of Comparative Example 11 was considered to exhibit excellent
magnetic properties as a material for a conventional magnetic head; since the crystallization
temperature is low, e.g., 380°C, it is crystallized by glass bonding at 500°C, and
the value of the effective magnetic permeability after bonding becomes extremely small.
[0045] On the other hand, the amorphous alloys of Examples 5 to 7 all have high crystallization
temperatures (higher than 500°C) and high saturation magnetization levels (higher
than 8 KGauss); sustain no deterioration in their effective magnetic permeabilities,
even from the gradual cooling which occurs after glass bonding; and exhibit saturation
magnetostriction constants of small value, such as on the order of 10
-7, as an absolute value.
[0046] According to the present invention, as described above, a magnetic head using an
amorphous alloy may be obtained, the magnetic properties of which are not influenced
by glass bonding.
[0047] It is to be noted here that the Hf used in the amorphous alloys for the magnetic
heads of Examples 5 to 7 were 99.8% pure; and, that, though such alloys are approx.
0.02% Zr in content, an impurity such as this (Zr) does not affect the advantages
of the present invention. Even where Hf of relatively low purity (such as one which
is 95% and is approx. 3% Zr in content) is employed, it has been confirmed that the
advantages of the amorphous alloy according to the present invention can still be
obtained.