Soft magnetic alloy films having a modulated nitrogen content

A nitrogen-containing Fe-based soft magnetic alloy suitable for use as the material of a magnetic head core, as well as a method for manufacturing the soft magnetic alloy film. Unlike a mere nitride alloy film, the soft magnetic alloy of the present invention has a compositionally modulated structure in which at least the nitrogen content is periodically modulated in the direction of thickness of the film so as to have a nitride layer rich at least in nitrogen and a non-nitride layer poor at least in nitrogen. The soft magnetic alloy film of the invention comprises a main constituent of Fe, at least one metalloid element selected from the group consisting of B, Si and C, and at least one metal element selected from the group consisting of Nb, Ta, Zr and Ti and has fine Fe-based grains included therein. By virtue of these film structure and film composition, the soft magnetic alloy film of the invention exhibits superior magnetic characteristics such as low coercive force, high saturation magnetization and low magnetostriction, as well as superior resistance both to corrosion and wear.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a nitrogen-containing Fe based soft 
magnetic alloy film suitable for use as the material of, for example, a 
core of a magnetic head. 
2. Description of the Prior Art 
Soft magnetic alloys used as the material of core of a magnetic head are 
required to have higher level of saturation magnetization to cope with 
recent demand for higher density of magnetic recording. On the other hand, 
in order to manufacture a practical magnetic head with a high reliability, 
it is important that a strong bonding with a bonding glass be made at the 
magnetic gap portion etc. of the magnetic head. In general, however, 
bonding glasses having high bonding strength exhibit a higher melting 
point. Soft magnetic alloy films, even if they exhibit high levels of 
saturation magnetization, are therefore required to exhibit good soft 
magnetic characteristics even after a heat treatment at a high 
temperature. Due to this restriction from the requirement concerning the 
thermal stability, conventional soft magnetic alloy films for magnetic 
heads used in VCR's, etc. have a practical upper limit of saturation 
magnetization on the order of 10 kGauss or so. In general, production of a 
soft magnetic alloy having superior soft magnetic characteristic 
essentially requires that the magnetic anisotropy and saturation 
magnetostriction constant .lambda.s be made as small as possible. Co-based 
amorphous alloy exhibits superior soft magnetic characteristics partly 
because of its magnetostriction constant .lambda.s being zero and partly 
because of its small magnetic anisotropy due to its amorphous state. 
Unfortunately, however, Co-based amorphous alloys generally exhibit lower 
saturation magnetization than Fe-base amorphous alloy represented by 
Fe-Si-B alloys. The use of the Co-based amorphous alloys also poses a 
problem from an economical point of view, because Co is considerably more 
expensive as compared with Fe. For these reasons, there has been a demand 
for ferrous soft magnetic alloys. The present inventors have discovered 
two types of Fe based magnetic alloys: namely, an Fe-Nb-B type alloy 
having magnetostriction constant .lambda.s of +1.times.10.sup.-5 and an 
Fe-Nb-Cu-B alloy having magnetostriction constant .lambda.s of 
+3.times.10.sup.-6, and proposed them in the specification of Japanese 
Patent Application No. 55-164978. These alloys exhibit improved wear 
resistance and corrosion resistance by virtue of addition of Nb but are 
rather inferior in thermal stability, wear resistance and corrosion 
resistance as compared with metal-metal amorphous alloys of Co-Nb-Zr type 
(see specifications of Japanese Patent Application Nos. 56-181723 and 
56-212873) which are currently used as the material of VCR magnetic heads. 
Nitriding is a measure which is available for improving wear resistance and 
corrosion resistance of the above-mentioned ferrous soft magnetic alloys. 
Studies such as a study on formation of nitride film through combination 
between Fe, Co, Ni and B, Si, Al, P, C etc. (see Japanese Patent 
Unexamined Publication No. 54-94428) and a study on Fe nitrides (see 
Journal of Applied Phys. Vol. 53 (11), pp 8332-34 (1982)) have been made 
in regard to nitriding of Fe based soft magnetic alloys. The technique 
disclosed in Japanese Patent Unexamined Publication No. 54-94428, however, 
encounters a problem in that the soft magnetic characteristic is seriously 
affected by an increase in the vertical magnetic anisotropy, and in that 
the level of the saturation magnetization is lowered. On the other hand, 
it has been reported that the technique disclosed in the Journal of 
Applied Phys. is disadvantageous in that the soft magnetic characteristic 
is impaired due to the fact that the coercive force of the alloy is 
increased as a result of nitriding of Fe. 
As has been described, nitrides of alloys containing Fe as the major 
constituent possess wear resistance and corrosion resistance equivalent to 
those of Co-Nb-Zr alloys which are practically used, as well as higher 
level of saturation magnetization than Co-based alloys. In addition, these 
nitrides are rather inexpensive and, hence, are advantageous from the view 
point of economy. Unfortunately, however, these nitrides are not expected 
to exhibit superior soft magnetic characteristics. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide an Fe-based 
soft magnetic alloy film for use in a magnetic head, which exhibits 
superior soft magnetic characteristics such as low coercive force after a 
heat treatment at a high temperature, as well as superior magnetic 
characteristics such as high level of saturation magnetization and low 
magnetostriction, while showing improved corrosion resistance and wear 
resistance, by employing a compositionally modulated structure produced by 
applying nitrogen to an Fe-based alloy film, rather than by application of 
a mere nitride alloy. 
To this end, according to the present invention, there is provided a soft 
magnetic alloy film containing at least one metalloid element selected 
from a group consisting of B, Si and C, at least one metal element 
selected from the group consisting of Nb, Ta, Zr and Ti, and a main 
constituent of Fe, the soft magnetic alloy film having a structure in 
which at least the nitrogen content is modified in the direction of 
thickness of the film so as to have a nitride layer rich at least in both 
nitrogen and metalloid element and a non-nitride layer poor at least in 
these nitrogen and metalloid elements, the structure containing fine 
crystal grains of Fe based alloy. 
The soft magnetic alloy of the present invention can be manufactured by a 
process comprising the steps of: forming an alloy film through a 
sputtering by using, as the target, an Fe-based alloy containing at least 
one metalloid element selected from a group consisting of B, Si and C, at 
least one metal element selected from the group consisting of Nb, Ta, Zr 
and Ti, and a main constituent of Fe, while periodically introducing and 
mixing nitrogen gas in the inert sputtering gas such as argon, so that a 
compositionally modulated nitride alloy film is obtained in which at least 
the nitrogen content is modified in the direction of thickness of the 
film; and subjecting said compositionally modulated nitride alloy film to 
a high-temperature heat treatment, whereby a soft magnetic alloy film is 
formed which has a film structure having a nitride layer rich at least in 
both nitrogen and metalloid element and a non-nitride layer poor at least 
in the nitrogen and metalloid element, and which film contains fine 
crystal grains of Fe based alloy. 
The invention provides a soft magnetic alloy film which specifically 
exhibit superior soft magnetic characteristics and high level of 
saturation magnetization, in which at least the nitrogen composition is 
modulated in the direction of thickness of the film and which has a mean 
film composition expressed by: 
EQU MaTbXcNd ... (1) 
wherein M represents an Fe-based metal selected from a group consisting of 
Fe, Fe-Co, Fe-Ni and Fe-Co-Ni, T represents at least one metal element 
selected from a group consisting of Nb, Ta, Zr and Ti, X represents at 
least one metalloid element selected from a group consisting of B, Si and 
C, and N represents nitrogen, and wherein the contents a, b, c and d of M, 
T, X and N in terms of atomic % are selected to satisfy the following 
conditions. 
EQU 60.ltoreq.a.ltoreq.90, 1.ltoreq.b.ltoreq.15, 2.ltoreq.c.ltoreq.25, 
1.ltoreq.d.ltoreq.25 and a+b+c+d=100 ..... (1') 
This soft magnetic alloy film exhibits specifically excellent soft magnetic 
characteristic when it has a compositionally modulated wavelength of not 
more than 50 nm in the direction of thickness of said film. 
This soft magnetic alloy film is produced by a method of manufacturing a 
soft magnetic alloy film comprising the steps of: forming an alloy film 
through sputtering by using, as the target, an alloy having a composition 
expressed by: 
EQU Ma'Tb'Xc' ..... (2) 
where M represents an Fe-based metal selected from a group consisting of 
Fe, Fe-Co, Fe-Ni and Fe Co-Ni, T represents at least one metal element 
selected from a group consisting of Nb, Ta, Zr and Ti and X represents at 
least one metalloid element selected from a group consisting of B, Si and 
C, and where the contents a', b' and c' of M, T and X in terms of atomic % 
are selected to satisfy the following conditions: 
EQU 70.ltoreq.a'.ltoreq.95, 1.ltoreq.b'.ltoreq.15, 3.ltoreq.c'.ltoreq.25 and 
a'+b'+c'+=100 ..... (2') 
while periodically introducing and mixing nitrogen gas in the inert 
sputtering gas such as argon at a rate expressed by: 
EQU 2%.ltoreq.Pn.ltoreq.20% ..... (2") 
where Pn represents the ratio of the nitrogen gas pressure to the total 
sputtering gas pressure during the sputtering expressed in terms of 
percentage, so that a compositionally modulated nitride alloy film is 
obtained in which at least the nitrogen content is modulated in the 
direction of thickness of the film and in which the compositionally 
modulated wavelength is not more than 40 nm; and subjecting said 
compositionally modulated nitride alloy film to a high-temperature heat 
treatment. 
The invention provides a soft magnetic alloy film which exhibits, in 
addition to superior soft magnetic characteristics and high level of 
saturation magnetization, low magnetostriction in which at least the 
nitrogen composition is modulated in the direction of thickness of the 
film and which has a mean film composition expressed by: 
EQU Ma"Tb"Xc"Nd" ..... (3) 
wherein M represents an Fe-based metal selected from a group consisting of 
Fe, Fe-Co, Fe-Ni and Fe-Co-Ni, T represents at least one metal element 
selected from a group consisting of Nb, Ta, Zr and Ti, X represents at 
least one metalloid element selected from a group consisting of B, Si and 
C, and N represents nitrogen, and wherein the contents a", b", c" and d" 
of M, T, X and N in terms of atomic % are selected to satisfy the 
following conditions. 
EQU 65.ltoreq.a".ltoreq.90, 1.ltoreq.b".ltoreq.10, 2.ltoreq.c".ltoreq.13, 
b.ltoreq.d".ltoreq.20 and a"+b"+c"+d"=100 ..... (3') 
Specifically excellent soft magnetic characteristics are obtained with the 
composition expressed by the formula (3) when the compositionally 
modulated wavelength in the direction of thickness of said film is 40 nm 
or smaller. 
This soft magnetic alloy film which exhibits low magnetostriction in 
addition to superior soft magnetic characteristics and high level of 
saturation magnetization, can be manufactured by a process comprising the 
steps of: forming an alloy film through a sputtering by using, as the 
target, an alloy having a composition expressed by: 
EQU Ma*Tb*Xc* ..... (4) 
where M represents an Fe-based metal selected from a group consisting of 
Fe, Fe-Co, Fe-Ni and Fe-Co-Ni, T represents at least one metal element 
selected from a group consisting of Nb, Ta, Zr and Ti and X represents at 
least one metalloid element selected from a group consisting of B, Si and 
C, and where the contents a*, b* and c* of M, T and X in terms of atomic % 
are selected to satisfy the following conditions: 
EQU 80.ltoreq.a*.ltoreq.95, 1.ltoreq.b*.ltoreq.12, 3.ltoreq.c*.ltoreq.15 and 
a*+b*+c*=100 .... (4') 
while periodically introducing and mixing nitrogen gas in the inert 
sputtering gas such as argon at a rate expressed by: 
EQU 5%.ltoreq.Pn.ltoreq.15% ..... (4") 
where Pn represents the ratio of the nitrogen gas pressure to the total 
sputtering gas pressure during the sputtering expressed in terms of 
percentage, so that a compositionally modulated nitride alloy film is 
obtained in which at least the nitrogen content is modulated in the 
direction of thickness of the film; and subjecting said compositionally 
modulated nitride alloy film to a high-temperature heat treatment 
conducted at a temperature not lower than 500.degree. C. 
A soft magnetic alloy film having extremely excellent soft magnetic 
characteristics such as high magnetic permeability is obtained by 
conducting, in the methods stated above, the high-temperature heat 
treatment in a magnetic field. 
The soft magnetic alloy film of the present invention is an Fe-based alloy 
containing metallic elements such as Nb, Ta, Zr and Ti and metalloid 
elements such as B, Si and C. Unlike ordinary pure nitride films, the soft 
magnetic alloy film of the present invention exhibits, after formation of 
the film by sputtering, a distinctive compositionally modulated structure 
in which the N content is modulated in the direction of thickness of the 
film, i.e., a laminated structure composed of a nitride layer rich in 
nitrogen and a non-nitride layer poor in nitrogen. The method of the 
invention for manufacturing a soft magnetic alloy film is a method for 
forming the soft magnetic alloy film of the present invention. According 
to the method of the present invention, an Fe-based compositionally 
modulated nitride alloy film is formed by sputtering, such that at least 
the N content is modulated in the direction of thickness of the film. 
Then, a heat treatment is effected on the as-sputtered compositionally 
modulated nitride alloy film at a high temperature so as to cause a change 
in the film structure, whereby a soft magnetic alloy film having both 
superior soft magnetic characteristics and high level of saturation 
magnetization is obtained. 
A description will be given of the method of the present invention for 
manufacturing a soft magnetic alloy film. 
The soft magnetic alloy film is formed by sputtering which is conducted by 
using, as the target, an Fe-based alloy containing at least one metalloid 
element selected from a group consisting of B, Si and C and at least one 
metal element selected from a group consisting of Nb, Ta, Zr and Ti, The 
sputtering is conducted in an inert spatter gas such as argon (Ar) while 
periodically introducing nitrogen gas N2 into the spattering gas, thus 
obtaining a compositionally modulated nitride alloy film in which at least 
the nitrogen content is modulated in the direction of the thickness of the 
film. The compositionally modulated nitride alloy film thus formed 
exhibits a distinctive compositionally modulated structure: namely, a 
laminated structure having a nitride layer rich in nitrogen and a 
non-nitride layer poor in nitrogen. When introduction of nitrogen gas is 
conducted during the sputtering, a reactive spatter is formed so that a 
nitride layer with nitrogen contained in the alloy film is formed. It is 
considered that the introduction of nitrogen into the alloy film is 
promoted when the target used in the sputtering contains an element such 
as Nb, Ta, Zr, ti or the like which exhibits a higher affinity to the 
nitrogen than Fe. The thicknesses of the nitride layer and the non-nitride 
layer are controllable through changing the period of introduction of the 
nitrogen gas during the sputtering. Thus, the sum of the thickness of the 
nitride layer and the thickness of the non-nitride layer per each 
sputtered layer determines the compositionally modulated wavelength. The 
compositionally modulated structure, in which at least the nitrogen 
content is modulated in the direction of the film thickness, can be 
confirmed by obtaining, for example, AES depth profiles of contained 
elements by use of, for example, Auger Electron Spectroscopy (AES). The 
nitride layer and the non-nitride layer have different composition ratios. 
The nitride layer having greater nitrogen content naturally has smaller 
contents of other elements as compared with the non-nitride layer. Thus, 
in the as-sputtered compositionally modulated nitride alloy film, the 
contents of the metalloid elements in the nitride layer are small as 
compared with the non-nitride layer. Thus, the metalloid elements and 
metal elements are contained in inverse phase in the direction of 
thickness of the film. The as-sputtered compositionally modulated nitride 
alloy film has an amorphous phase, or a crystalline phase with extremely 
small crystal grain size or their mixture. The as-sputtered 
compositionally modulated nitride alloy can have a high level of 
saturation magnetization provided that the composition of the alloy target 
is suitably selected in the sputtering, but the soft magnetic 
characteristics are still unsatisfactory. Thus, the as-sputtered 
compositionally modulated nitride alloy film cannot be used as the 
material of magnetic heads, unless a suitable heat-treatment is conducted 
subsequently to the sputtering. 
After the heat treatment at a high temperature, the sputtered 
compositionally modulated nitride alloy film exhibits both superior soft 
magnetic characteristics and high level of saturation magnetization. The 
compositionally modulated structure of the compositionally modulated 
nitride alloy film largely vary as a result of the heat treatment at high 
temperature, because of both fusion of the constituents and precipitation 
of fine grains of Fe based alloy during the heat treatment. However, the 
modulation of the nitrogen content in the direction of thickness of the 
film remains even after the heat treatment. In contrast, a single-layered 
pure nitride film which is nitrided uniformly, can hardly exhibit soft 
magnetic characteristics and does not exhibit any improvement in the 
magnetic characteristics even through a heat treatment. It is therefore a 
critical and essential condition that the nitrogen content is 
compositionally modulated in the direction of thickness of the film, in 
order to obtain a superior soft magnetic alloy film. The soft magnetic 
alloy film after the heat treatment at high temperature has a film 
structure which includes a nitride layer rich in at least both nitrogen 
and metalloid elements and a non-nitride film poor in at least nitrogen 
and metalloid elements, and has fine grains of Fe based alloy. An AES 
profile analysis of the soft magnetic alloy film after the 
high-temperature heat treatment will show that the contents of the 
metalloid elements are greater in the nitride layer than in the 
non-nitride layer and that the Fe content is greater in the non-nitride 
layer than in the nitride layer. Thus, although the soft magnetic alloy 
film prepared before the high temperature heat treatment contains the 
metalloid elements and nitrogen element in an inverse phase relation to 
each other, the soft magnetic alloy film obtained after the 
high-temperature heat treatment exhibits the same phase relation with 
respect to the contents of the metalloid elements and nitrogen element 
This may be attributed to a special manner of diffusion caused by the fact 
that the metalloid elements such as B, Si and C exhibit greater tendency 
of bonding to nitrogen than to Fe. An alloy film cross-sectional image 
obtained through a transmission electron microscope of the soft magnetic 
alloy film obtained after the high-temperature heat treatment showed 
numerous fine crystal grains of grain sizes not more than 20 nm in and 
around the non-nitride layer. An X-ray diffraction proved that these fine 
crystal grains are .alpha.-Fe grains having a body-centered cubic lattice. 
It is considered that the .alpha.-Fe grains have been produced as a result 
of the fact that the non-nitride layer has been extremely enriched in Fe 
as a result of the specific diffusion caused by the high-temperature heat 
treatment. It is considered that the grain growth of the fine Fe-base 
crystal grains is suppressed during the heat treatment, due to presence of 
nitride layer, so that the soft magnetic alloy film obtained after the 
heat treatment exhibits superior thermal stability of the soft magnetic 
characteristics. Thus, the high-temperature heat treatment causes a change 
in the structure of the alloy film so that the soft magnetic alloy film 
obtained after the high-temperature heat treatment exhibits superior soft 
magnetic characteristics with reduced coercive force and increased level 
of saturation magnetization. It is therefore considered that both the 
special manner of diffusion of elements caused by the high-temperature 
heat treatment and the resultant generation of fine crystal grains of Fe 
contribute to the realization of the soft magnetic characteristics. The 
method of the invention for manufacturing the soft magnetic alloy film s 
suitable for use in the production of magnetic head cores because it 
provides superior soft magnetic characteristics after the high-temperature 
heat treatment. 
A description will be given of the soft magnetic alloy in accordance with 
the present invention. The soft magnetic alloy film of the present 
invention is a kind of nitride alloy containing nitrogen and, therefore, 
exhibits superior corrosion-resistance and wear-resistance 
characteristics. The soft magnetic alloy film of the present invention, 
however, is not a mere nitride film but is a film having a distinctive 
compositionally modulated structure in which at least the nitrogen content 
is modulated in the direction of thickness of the film. Thus, elements 
having small affinity to nitrogen, e.g., Fe, and elements having high 
levels of affinity to nitrogen, e.g.,metalloid elements such as B, Si, C 
and etc. and metal elements such as Nb, Ta, Zr, Ti and etc., exist in the 
alloy film. It is considered that, in the soft magnetic alloy film of the 
invention obtained after the high-temperature heat treatment, elements 
such as B, Si, C, Nb, Ta, Zr, Ti, etc. are selectively bonded chemically 
to nitrogen with high levels of bonding strength The presence of these 
elements is important for obtaining superior soft magnetic characteristics 
through the high-temperature heat treatment. The metallic elements such as 
Nb, Ta, Zr, Ti and so forth are necessary for the purposes of facilitating 
introduction of nitrogen into the alloy film during the reactive 
sputtering, realizing thermally stable soft magnetic characteristics after 
the high-temperature heat treatment and improving both corrosion- and 
wear-resistance characteristics. The metalloid elements such as B, Si, C 
and so forth are necessary for enabling the special manner of diffusion 
through high-temperature heat treatment to thereby facilitate realization 
of superior soft magnetic characteristics. Therefore, the soft magnetic 
alloy of the present invention is an Fe-based alloy film containing Fe as 
a main constituent, at least one metalloid elements selected from a group 
consisting of B, Si and C, and at least one metal element selected from 
the group consisting of Nb, Ta, Zr and Ti. 
The alloy film having the composition expressed by the composition formula 
(1) enables production of a soft magnetic alloy having particularly 
superior magnetic characteristic and high saturation magnetization. In 
order to obtain a soft magnetic alloy film having high levels of 
saturation magnetization, the content a of M, content b of T, content c of 
X and the content d of N in the mean composition of the film, expressed in 
terms of atomic %, are to be determined to meet the conditions of 
a.gtoreq.60, b.ltoreq.15, c.ltoreq.25 and d.ltoreq.25. Conversely, for 
obtaining superior soft magnetic characteristics, it is necessary that 
that the conditions of a.ltoreq.90, b.gtoreq.1, 2.ltoreq.c.ltoreq.25 and 
1.ltoreq.d.ltoreq.25 are met. In order to obtain a soft magnetic alloy 
film superior both in resistances to corrosion and wear and the soft 
magnetic characteristics, it is necessary that the conditions of 
b.gtoreq.1, c.ltoreq.25 and d.gtoreq.1 are met. In order to attain an 
appreciable effect in improving the corrosion resistance, it is necessary 
that the content d of nitrogen is not smaller than 1 atomic %. Conversely, 
the nitrogen content d exceeding 25 atomic % is not adoptable because such 
a high nitrogen content causes exfoliation of the alloy film. The 
above-mentioned ranges of contents are expressed by formula (1'). It is 
possible to obtain a soft magnetic alloy film having specifically 
excellent soft magnetic characteristic provided that the compositionally 
modulated wavelength is determined to be not more than 50 nm. Oxygen may 
be incidentally included in the soft magnetic alloy film but this does not 
cause any problem if the content of oxygen is sufficiently small. 
In order to obtain the soft magnetic alloy film of the composition (1) by 
sputtering, an alloy target of the composition formula (2) is essentially 
required considering that nitrogen is contained in the alloy film during 
the sputtering. According to the method of the invention for producing a 
soft magnetic alloy film, the soft magnetic alloy film expressed by the 
composition formula (1) is obtained by forming a compositionally modulated 
nitride alloy film, using the alloy target of the composition formula (2) 
and then effecting a high-temperature heat treatment on the thus formed 
alloy film. In order that this soft magnetic alloy film can have high 
level of saturation magnetization, the content a' of M, content b' of T, 
and the content c' of X in the formula (2) expressed in terms of atomic %, 
are to meet the conditions of a'.gtoreq.70, b'.ltoreq.15, c.ltoreq.25. For 
obtaining superior soft magnetic characteristics, it is necessary that 
that the conditions of a'.ltoreq.95, b'.gtoreq.1 and 3.ltoreq.c'.ltoreq.25 
are met. Thus, in order that both requirements are met, the composition 
has to meet the conditions of 70.ltoreq.a'.ltoreq.85, 
1.ltoreq.b'.ltoreq.15', 3.ltoreq.c'.ltoreq.25 and a'+b'+c'=100. These 
conditions are synthetically shown in the formula (2'). The rate of the 
periodical introduction of the nitrogen gas into the inert sputtering gas 
such as argon during the formation of the alloy film is expressed by the 
partial pressure ratio Pn in terms of percentage to the total sputtering 
gas pressure. In order to obtain the soft magnetic alloy of the formula 
(1), it is necessary that the conditions of 2(%).ltoreq.Pn.ltoreq.20(%) be 
met as expressed by the formula (2"). The method of the invention employs, 
for the purpose of manufacturing the soft magnetic alloy film expressed by 
the composition (1), the steps of forming a compositionally modulated 
nitride alloy film in which at least the nitrogen composition is modulated 
in the direction of thickness of the film, through a sputtering process 
which is conducted by employing the above-specified target and the 
above-specified nitrogen partial pressure, and then conducting a 
high-temperature heat treatment on the thus formed film at a temperature 
which is not lower than 300.degree. C. 
The composition formula (3) shows the mean composition of an alloy film of 
the present invention which exhibits a low magnetostriction in addition to 
the excellent soft magnetic characteristics and the high level of 
saturation magnetization. The term "low magnetostriction" is used to mean 
that the magnetostriction constant is zero or near zero. The composition 
shown in the formula (3) contains M, T, X and N as in the case of the 
composition of the formula (1) but the composition ranges of these 
elements are restricted from the composition ratios shown in the formula 
(1'). Namely, in order to simultaneously meet both the demands for the low 
magnetostriction and high saturation magnetization, the contents a", b", 
c" and d" of M, T, X and N, respectively, in terms of atomic % should be 
determined to meet the condition of a".gtoreq.65, b".ltoreq.10, 
2.ltoreq.c".ltoreq.13 and 5.ltoreq.d".ltoreq.20. These composition ranges 
and the composition ranges shown by the formula (1') are synthetically 
shown in the formula (3"). It is possible to obtain a soft magnetic alloy 
having specifically high magnetic permeability and low coercive force, 
provided that the compositionally modulated wavelength of the 
compositionally modulated nitride alloy film is determined to be not 
greater than 40 nm. Inclusion of oxygen in this soft magnetic alloy is 
inevitable also in this case, but this does not cause any substantial 
problem if the oxygen content is sufficiently small. 
In order to obtain through a sputtering a soft magnetic alloy of the 
formula (3) which has both low magnetostriction and high saturation 
magnetization, it is necessary to employ an alloy target of the 
composition shown by the formula (4) and the nitrogen gas partial pressure 
Pn as specified by the formula (4"). The contents a*, b* and c* of the 
elements M, T and X in the formula (4), in terms of atomic %, should be 
determined to meet the conditions of 80.ltoreq.a*.ltoreq.95, 
1.ltoreq.b*.ltoreq.12 and 3.ltoreq.c*.ltoreq.15 and a*+b*+c*=100. These 
composition ranges are synthetically shown by the formula (4'). The rate 
of the periodical introduction of the nitrogen gas into the inert 
sputtering gas such as argon during the formation of the alloy film is 
expressed by the partial pressure ratio Pn in terms of percentage to the 
total sputtering gas pressure. In order to obtain the soft magnetic alloy 
of the formula (3), it is necessary that the conditions of 5(%).ltoreq. 
Pn.ltoreq.15(%) be met as expressed by the formula (4"). The method of the 
invention employs, for the purpose of manufacturing the soft magnetic 
alloy film expressed b the composition (3), the steps of forming a 
compositionally modulated nitride alloy film in which at least the 
nitrogen composition is modulated in the direction of thickness of the 
film, through a sputtering which is conducted by employing the 
above-specified target and the above-specified nitrogen partial pressure, 
and then conducting a high-temperature heat treatment on the thus formed 
film at a temperature which is not lower than 500.degree. C. 
According to the method of the present invention, it is possible to obtain 
a soft magnetic alloy film having an extremely superior magnetic alloy 
characteristics such as high magnetic permeability, when the as-sputtered 
compositionally modulated nitride alloy film is heat-treated at a high 
temperature within a magnetic field. The effect produced by a 
heat-treatment in a magnetic field has been commonly recognized as 
induction magnetic anisotropy as experienced with the cases of amorphous 
alloys and permalloys. The present inventors have confirmed that the heat 
treatment in a magnetic field is effective also in crystalline alloy films 
having the compositionally modulated structure as described and containing 
Fe as a main constituent. More specifically, it is possible to improve the 
magnetic permeability of the soft magnetic alloy applying a magnetic field 
of 1 (Oe) or stronger during the high-temperature treatment. The 
as-sputtered compositionally modulated nitride alloy film or the soft 
magnetic alloy obtained after the high-temperature heat treatment may 
incidentally contain oxygen. This, however, does not cause any problem 
provided that the oxygen content is sufficiently small. 
The soft magnetic alloy of the present invention exhibits improved wear 
resistance and corrosion resistance by virtue of the nitriding. In 
addition, excellent soft magnetic characteristics and superior thermal 
stability are ensured by the compositionally modulated structure. In 
addition, the soft magnetic alloy of the invention contains Fe as a main 
constituent which provides a high level of saturation magnetization and 
which enables an economical production.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIrst Embodiment 
As a first embodiment, soft magnetic alloy film of the present invention 
was produced by the method of the invention for producing a soft magnetic 
alloy film, using an alloy target having a composition expressed by 
Fe.sub.79.5 Nb.sub.6 Si.sub.3 B.sub.11.5. This first embodiment will be 
described in detail hereinunder. 
A sputtering was conducted on a ceramic substrate using the above-mentioned 
alloy target while periodically mixing nitrogen gas N.sub.2 in the argon 
gas which was used as the inert sputtering gas, whereby a compositionally 
modulated nitride alloy film was formed on the ceramic substrate such that 
nitride layers of 10 nm thick per layer and non-nitride layers of 10 nm 
thick per layer were alternately formed. The ratio of the nitrogen gas 
introduced during the sputtering is expressed in terms of the partial 
pressure Pn (%) of nitrogen. In this case, the nitrogen gas partial 
pressure was Pn=10(%). The sum of the thickness of one non-nitride layer 
is defined as the compositionally modulated wavelength. In this case, the 
compositionally modulated wavelength was 20 nm. The as-sputtered 
composition-modified nitride alloy film exhibited magnetic characteristics 
such as a saturation magnetization level of 9.6 kGauss and a coercive 
force of 11 Oe which are quite far from satisfying requirements for 
materials of a magnetic head core. For the purpose of comparison, 
sputtering was conducted by using the same target as the embodiment, in 
which argon gas alone was used as the sputtering inert gas so that a 
single non-nitride layer was formed. Similarly, a film was formed by using 
the same target, in a mixture sputtering inert gas of a fixed ratio of 
nitrogen and argon gases so that a single nitride layer was formed. In the 
following description of the preferred embodiment, the term CMNF is used 
to mean the compositionally modulated nitride alloy film. 
The alloy films having the above-described various structures were 
heat-treated in a rotating magnetic field. The single nitride layer which 
was uniformly nitride did not show any soft magnetic characteristic and 
failed to show any improvement in the magnetic characteristics even after 
the heat treatment. On the other hand, the single non-nitride layer 
exhibited coercive force which was reduced after a heat treatment at about 
400.degree. to about 450.degree. C. but the coercive force was increased 
due to recrystallization when the heat-treating temperature was raised to 
500.degree. C. or above. In contrast, the compositionally modulated 
nitride alloy film prepared in accordance with the method of the present 
invention showed low levels of coercive fore after heat treatment 
conducted at temperatures between 350.degree. and 600.degree. C., as will 
be realized from FIG. 1 which shows the relationship between the 
heat-treating temperature Tann (.degree.C.) and the coercive force Hc(Oe) 
of the compositionally modulated nitride alloy after 1-hour heat treatment 
at each temperature. FIG. 2 shows the relationship between the 
heat-treating temperature Tann (.degree.C.) and saturation magnetization 
(4 .pi.Ms) of the compositionally modulated nitride film at room 
temperature. From this Figure, it will be seen that the level of the 
saturation magnetization increases when the heat treating temperature is 
300.degree. C. or above. It is therefore understood that the heat 
treatment is conducted at a temperature of 300.degree. C. or higher in 
order to simultaneously obtain both excellent soft magnetic 
characteristics and high level of saturation magnetization. The dependency 
of the magnetic characteristics of the compositionally modulated nitride 
alloy film on the heat-treating temperature is closely related to the 
change in the structure of the alloy film. The difference between the film 
structure of the compositionally modulated nitride alloy film before the 
heat treatment and that after the heat treatment will be discussed 
hereinunder. 
FIGS. 3(a) to 3(c) show an AES (Auger Electron Spectroscopy) profile 
concerning the contents of Fe, N and B in the direction of the film 
thickness as measured by an Auger Electron Spectroscopy. More 
specifically, FIG. 3(a) shows the AES depth profile as observed with the 
as-sputtered compositionally modulated nitride alloy film before the 
high-temperature heat treatment. FIG. 3(b) shows the AES depth profile as 
observed after 1-hour high-temperature heat treatment at 500.degree. C., 
while FIG. 3(c) shows that after 1-hour high-temperature heat treatment at 
680.degree. C. It will be seen from FIG. 3(a) that the as-sputtered 
structure has a nitride layer rich in N and a non-nitride layer poor in N 
and rich in Fe and B. Thus, Fe and B are contained in the same phase 
relation to each other and in opposite phase relation to N in the 
direction of thickness of the film. In contrast, in the structures after 
the heat treatment, as shown in FIGS. 3(b) and 3(c), the B content is 
greater in the nitride layer than in the non-nitride layer, while the Fe 
content is greater in the non-nitride layer than in the nitride layer. 
That is, N and B appear in the same phase relation in the direction of the 
film thickness, and N and B are in an opposite phase relation to Fe. Thus, 
the heat temperature at high temperature causes a change from a state in 
which N and B appear in opposite phase relation to each other into another 
state in which N and B appear in the same phase relation to each other in 
the direction of the film thickness. This is attributable to a special 
manner of diffusion caused by the fact that the metalloid elements such as 
B exhibit greater tendency of bonding to nitrogen than to Fe. Si which 
also is a metalloid element appears in the same phase relation as N and B 
before and after the high-temperature heat treatment. The same applies 
also to Nb which is a metal element. In a case of Nb, however, the degree 
of compositional modulation is comparatively small. FIGS. 4(a) to 4(c) 
show X-ray diffraction patterns as obtained with the alloy film in the 
states before and after high-temperature heat treatment. More 
specifically, FIG. 4(a) shows the X-ray diffraction pattern as observed 
with the as-sputtered compositionally modulated nitride alloy film in the 
state before the high-temperature heat treatment. It is considered that 
the structure of the alloy film in this state has an amorphous state or a 
very fine crystalline state with extremely fine grains or a mixture 
thereof. FIGS. 4(b) and 4(c) show the X-ray diffraction patterns as 
observed after 1-hour heat treatment at 500.degree. C. and 680.degree. C., 
respectively. In each of the cases shown in FIGS. 4(b) and 4(c), the 
structure is crystalline and .alpha.-Fe with body centered cubic lattice 
is observed. Judging from the peak levels and the half-value widths, 
however, both crystalline structures are predicted to be very fine 
structures. An electron-microscopic observation of cross-section of an 
actual soft magnetic alloy after the high-temperature heat treatment 
showed numerous fine crystal grains of grain size of 20 nm or smaller in 
and around the non-nitride layer. These fine grains are Fe crystal grains. 
It is considered that the generation of fine Fe crystal grains is promoted 
by the enrichment of Fe in the non-nitride layer as a result of the 
special manner of diffusion caused by the heat-treatment and that the 
growth of these grains is suppressed during the heat-treatment due to 
presence of the nitride layer. The Fe based fine crystal grains of grain 
sizes of not more than 20 nm are considered to make a contribution to the 
realization of the soft magnetic characteristic. In order to facilitate 
production of the fine crystal grains of sizes not greater than 20 nm, it 
is advisable that the nitride layer and the non-nitride layer of the 
as-sputtered compositionally modulated nitride alloy film have thicknesses 
not greater than 20 nm, i.e., that the compositionally modulated 
wavelength of the compositionally modulated nitride alloy film be 
maintained to be not more than 20 nm. This is also supported by FIG. 5 
showing the relationship between the coercive force (Hc) and the 
compositionally modulated wavelength (.lambda.) of the soft magnetic alloy 
film after 1-hour high-temperature heat treatment at 500.degree. C., 
wherein the coercive force exhibits an appreciable reduction in the range 
of .lambda..ltoreq.40nm. 
As has been discussed, the soft magnetic alloy film in accordance with the 
present invention exhibits both a low level of coercive force and high 
saturation magnetization as a result of a change in the alloy film 
structure caused by the heat treatment at high temperature. The fact that 
superior soft magnetic characteristics are obtained through a 
high-temperature heat treatment is advantageous when this alloy is 
intended for use as a soft magnetic alloy film for magnetic head cores. It 
is also possible to improve characteristics such as magnetic permeability, 
when the high-temperature heat treatment of the as-sputtered 
compositionally modulated nitride alloy film is conducted in a magnetic 
field. In the first embodiment, the soft magnetic alloy film after 1-hour 
high-temperature heat treatment at 500.degree. C. in the absence of any 
magnetic field exhibited an initial magnetic permeability of about 800 at 
1 MHz. In contrast, when the heat treatment was conducted for 1 hour at 
500.degree. C. in a fixed magnetic field of 400 Oe, the initial magnetic 
permeability as measured in the direction of axis of difficult 
magnetization was about 3000 at 1 MHz, thus proving the improvement in the 
soft magnetic characteristics by the heat treatment conducted in a 
magnetic field. The effect produced by the heat treatment in magnetic 
field has been recognized as induction magnetic anisotropy as in the cases 
of amorphous alloys and permalloys. According to the invention, it has 
been confirmed that the heat treatment in a magnetic field is effective 
also in the case of a crystalline alloy film containing Fe as a main 
constituent. 
Compositionally modulated nitride alloy films (CMNF) were prepared by using 
the above-mentioned alloy target while the nitrogen gas partial pressure 
Pn and the composition modification wavelength .lambda. were varied, and 
these alloy films were heat-treated at high temperatures so that samples 
of the soft magnetic alloy films of the present invention were fabricated. 
Levels of coercive force, corrosion resistance and wear amount ratio of 
Sample Nos. 1 to 7 are shown in Table 1, together with those of comparison 
sample Nos. 8 to 10 having various different structures. 
TABLE 1 
__________________________________________________________________________ 
Nitrogen 
Composi- 
gas partial 
tionally 
pressure 
modulated 
Coercive Wear 
Sample ratio wavelength 
force 
Corrosion 
resis- 
Nos. 
structure 
Pn (%) 
.lambda.(nm) 
Hc (Oe) 
resistance 
tance 
__________________________________________________________________________ 
Examples 
1 Compositionally 
5 10 0.6 .circle. 
0.6 
of 2 modulated 
5 20 0.6 .circle. 
0.7 
Embodiment 
3 nitride film 
10 10 0.5 .circle. 
0.5 
4 10 20 0.6 .circle. 
0.5 
5 10 40 2 .circle. 
0.6 
6 15 10 0.6 .circle. 
0.6 
7 15 20 0.7 .circle. 
0.5 
Comparison 
8 Compositionally 
10 100 6 .DELTA. 
0.7 
Example modulated 
nitride film 
9 Single-layered 
10 -- &gt;20 .circle. 
0.5 
nitride film 
10 Single-layered 
-- -- 0.6 X 1 
non-nitride film 
__________________________________________________________________________ 
In Table 1 the term "corrosion resistance" is used to mean the results of 
microscopic observation of degree of rust on the samples after 24-hour 
immersion of the samples in pure water. Marks , .DELTA. and X are used to 
mean, respectively, the state in which no rust was observed (excellent 
corrosion resistance), the state in which slight rust was observed and the 
state in which considerably heavy rust was observed (inferior corrosion 
resistance). The wear amount ratio is expressed in terms of the relative 
values of worn volume of the alloy films after a test running of a metal 
tape in a VCR tape running system. The greater value of the wear amount 
ratio indicates greater tendency of wear. 
As will be seen from Table 1, Sample Nos. 1 to 7 which are the soft 
magnetic alloy film of the present invention exhibit superior soft 
magnetic characteristic represented by low levels of coercive force, as 
well as excellent corrosion- and wear-resistance. From the comparison 
between the samples of the alloy films of the invention and the Comparison 
Sample No. 8, it is understood that the compositionally modulated 
wavelength is preferably not greater than 50 nm, in order to obtain a 
compositionally modulated film which is superior in all aspects. 
Table 2 shows the levels of the saturation magnetization 4 .pi.Ms and the 
saturation magnetostriction constant .lambda.s of Sample Nos. 11 to 13 of 
the soft magnetic alloy film of the invention, in comparison with those of 
Comparison Example Nos. 14 and 15. The alloy films of Sample Nos. 11 to 13 
of the invention were heat-treated at temperatures of 400.degree. to 
500.degree. C. The saturation magnetostriction constant was determined 
from a change in the anisotropic magnetic field which change occurs b 
bending, on an assumption that the Young's modulus was 150 Mpa. 
TABLE 2 
__________________________________________________________________________ 
Nitrogen 
Composi- Saturation 
gas partial 
tionally 
Saturation 
magnetostric- 
pressure 
modulated 
magnetization 
tion constant 
Sample ratio wavelength 
4n Ms .lambda.s 
Nos. 
Sample structure 
Pn (%) 
.lambda.(nm) 
(k G) (.times. 10.sup.-6) 
__________________________________________________________________________ 
Examples 
11 Compositionally 
10 10 12.6 +4 
of 12 modulated film 
10 20 12.4 +5 
Embodiment 
13 10 40 12 +7 
Comparison 
14 Single-layered 
10 -- 9.1 -- 
Example nitride film 
15 Single-layered 
-- -- 7.6 +12 
non-nitride film 
__________________________________________________________________________ 
As will be seen from Table 2, Sample Nos. 11 to 13 prepared in accordance 
with the invention exhibit very high levels of saturation magnetization as 
compared with Comparison Example 15 which is a single non-nitride alloy 
film. Thus, the Sample Nos. 11 to 13 are considered to exhibit superior 
recording characteristics when applied to, for example, magnetic head 
cores. Sample Nos. 11 to 13 also exhibit lower level of magnetostriction 
than Comparison Example 15 which is a single non-nitride alloy film. 
Practical Fe-based amorphous alloys generally exhibit greater saturation 
magnetostriction constant as the saturation magnetization level becomes 
higher. Sample Nos. 11 to 13 exhibit higher saturation magnetization level 
and smaller magnetostriction constant values as compared with Fe-based 
amorphous alloy. 
As have been described, soft magnetic alloy films of the first embodiment 
exhibits superior soft magnetic characteristics, high level of saturation 
magnetization and low magnetostriction, as well as excellent thermal 
stability which ensures that the soft magnetic characteristics are never 
impaired even by heat treatment at a high temperature. In addition, 
corrosion resistance and wear-resistances also are excellent. 
Second Embodiment 
A second embodiment will be described below. 
Sputtering was conducted on a ceramic substrate by using an alloy target 
having a composition expressed by Fe.sub.79.5 Nb.sub.8.5 Si.sub.12 (atomic 
%), while periodically mixing nitrogen gas into the Ar gas which was used 
as the inert sputtering gas, whereby a compositionally modulated nitride 
alloy film was formed on the ceramic substrate such that nitride layer of 
10 nm thick per layer and non-nitride layer of 10 nm thick per layer were 
alternately deposited. In some cases, the sputtering was conducted with 
the nitrogen gas partial pressure ratio Pn of 5%, while, in other cases, 
the nitrogen gas partial pressure ratio Pn was increased to 10%. 
The as-sputtered compositionally modulated nitride alloy film before the 
high-temperature heat treatment, as obtained by sputtering at Pn=10%, 
exhibited a saturation magnetization level of 9 kGauss and a coercive 
force of 7.6 Oe, whereas, in the cases of the as-sputtered compositionally 
modulated nitride alloy film obtained at Pn=5%, the levels of the 
saturation magnetization and the coercive force were 9.6 kGauss and 7.5 
Oe, respectively. These values are unsatisfactory when these materials are 
intended for use as magnetic head core materials. The as-sputtered 
compositionally modulated nitride alloy films were then subjected to 
1-hour heat treatment at 500.degree. C. conducted in a fixed magnetic 
field of 400 Oe, so that soft magnetic alloy films were obtained. The soft 
magnetic alloy film obtained at Pn=5% exhibited a saturation magnetization 
level of 12 kGauss and a coercive force of 0.4 Oe, whereas, in the cases 
of the soft magnetic alloy film obtained at Pn=10%, the levels of the 
saturation magnetization and the coercive force were 11.7 kGauss and 0.6 
Oe, respectively. Thus, these soft magnetic alloy films showed high levels 
of saturation magnetization, as well as excellent soft magnetic 
characteristics. When the high-temperature heat treatment was conducted in 
a magnetic field, the soft magnetic alloy film exhibited a good initial 
magnetic permeability of about 1000 or higher at 1 MHz as measured in the 
direction of axis of difficult magnetization. 
FIGS. 6(a) and 6(b) show AES depth profiles concerning Fe, N and Si in the 
direction of the film thickness as obtained through Auger Electron 
Spectroscopy. More specifically, FIG. 6(a) shows the compositionally 
modulated nitride alloy film in the state before high-temperature heat 
treatment, while FIG. 6(b) shows the state of the soft magnetic alloy film 
as obtained through 1-hour heat treatment at 500.degree. C. As will be 
seen from FIG. 6(a), the as-sputtered compositionally modulated nitride 
alloy film has a nitride layer rich in N and a non-nitride layer rich in 
Si. In contrast, in the soft magnetic alloy film obtained through the 
high-temperature heat treatment, the Si content is greater in the nitride 
layer than in the non-nitride layer, while the Fe content is greater in 
the non-nitride layer than in the nitride layer, as will be seen from FIG. 
6(b). This is attributable to a special manner of diffusion caused by the 
fact that the metalloid elements such as Si exhibits a greater tendency of 
bonding to nitrogen than to Fe. In this embodiment, the compositional 
modulation caused by the high-temperature heat treatment is unclear with 
respect to Nb which is a metallic element. It has been confirmed, however, 
a film structure composed of a nitride layer rich in nitrogen and 
metalloid elements and a non-nitride layer poor in nitrogen and metalloid 
elements and, hence, superior soft magnetic characteristics are obtainable 
through a high-temperature heat treatment, even when an Fe-Nb-Si ternary 
alloy is used as the target for the spattering. It is considered that a 
substantially equivalent effect will be obtained if Si is replaced by C 
which exhibits properties similar to those of Si. 
Third Embodiment 
A description will be given of a third embodiment of the present invention 
which is a soft magnetic alloy film having excellent soft magnetic 
characteristics and high resistances to corrosion and wear, as well as 
specifically high level of saturation magnetization and low level of 
magnetostriction. 
A sputtering was conducted by using an alloy target having a composition 
expressed by Fe.sub.85 Nb.sub.5 Si.sub.2 B.sub.8 (atomic %) while 
periodically mixing nitrogen gas with the sputtering argon gas at a 
nitrogen gas partial pressure ratio Pn of 0 to 20%, whereby a 
compositionally modulated nitride alloy film was formed to have a 
multi-layered structure composed of nitride layers of 10 nm thick per 
layer and non-nitride layers of 10 nm thick per layer which were 
periodically laminated in the direction of thickness of the film. The 
conditions of sputtering was varied so that different compositionally 
modulated nitride alloy film was obtained to have thicknesses of 1 to 3 
.mu.m. The thus-obtained as sputtered compositionally modulated nitride 
alloy films were subjected to heat treatment in a fixed magnetic field. 
FIG. 7 shows the relationship between the nitrogen gas partial pressure 
ratio Pn and the coercive force Hc and the initial magnetic permeability 
.mu..sub.i of the alloy film obtained through 1-hour heat treatment 
conducted at 500.degree. C. Similarly, FIG. 8 shows the relationship 
between the nitrogen gas partial pressure ratio Pn and the saturation 
magnetization 4 .pi.Ms of the alloy film obtained through 1-hour heat 
treatment conducted at 500.degree. C. From FIGS. 7 and 8, it will be 
understood that excellent soft magnetic characteristics and extremely high 
level of saturation magnetization are obtainable after the high 
temperature heat treatment when the preceding sputtering is conducted at 
nitrogen partial pressure ratio Pn ranging between 5 and 15%. It is to be 
noted that the soft magnetic alloy films formed under the conditions of 
Pn=5 to 15% has superior initial magnetic permeability of 1000 to 3000. 
FIG. 9 shows the relationship between the nitrogen partial pressure ratio 
Pn and the saturation magnetostriction .lambda.s exhibited by the soft 
magnetic alloy films as obtained through 1-hour heat treatment at 
500.degree. C., 550.degree. C. and 600.degree. C. The saturation 
magnetostriction constant as shown in FIG. 9 has been simply determined 
from a change in the anisotropic magnetic field after application of a 
bending stress, on an assumption that the Young's modulus is 150 Mpa. In 
this type of soft magnetic alloy film, the value of the magneto-striction 
constant varies according to the heat treating temperature. It is to be 
noted, however, that the magnetostriction constant is remarkably reduced, 
more particularly substantially to zero or near zero, after a heat 
treatment conducted at 500 to 600.degree. C when the sputtering was 
conducted at the nitrogen partial pressure ratio Pn of 5 to 15%. 
Generally, an alloy film composition formed by sputtering tends to deviate 
from the composition of the alloy target. In the case of the alloy film 
mentioned above, when the partial pressure ratio Pn is 0%, the 
single-layered non-nitride alloy film has a composition expressed by 
Fe.sub.86.5 Nb.sub.4.5 Si.sub.2 B.sub.7. THus, the Fe content of the alloy 
film is greater than that in the alloy target. In the soft magnetic alloy 
film of the present invention, the composition ratios of the elements such 
as Fe, Nb and B are reduced because of inclusion of nitrogen. For 
instance, the soft magnetic alloy film of the described embodiment, which 
is formed under the condition of Pn=7.5% and which shows a specifically 
superior magnetic characteristics, exhibit a composition which expressed 
substantially by Fe.sub.76 Nb.sub.4 Si.sub.2 B.sub.6 N.sub.12. According 
to the invention, it is possible to obtain, by forming a compositionally 
modulated nitride film at a nitrogen partial pressure ratio Pn ranging 
between 5 and 15 and then effecting a high-temperature heat treatment at 
500.degree. C. or higher, a soft magnetic alloy film exhibiting superior 
soft magnetic characteristics and high resistances to corrosion and wear, 
as well as specifically high level of saturation magnetization and low 
magnetostriction. Thus, a soft magnetic alloy film of the invention which 
simultaneously have both extremely high saturation magnetization and 
extremely low magnetostriction can be formed by conducting the sputtering 
with an alloy target which is rich in Fe and comparatively poor in metal 
and metalloid elements as represented by formulae (4) and (4') at a 
nitrogen partial pressure ratio as indicated by the formula (4"). 
As has been described, the third embodiment of the soft magnetic alloy in 
accordance with the present invention, which is comparatively rich in Fe, 
exhibits an extremely high level of saturation magnetization of 15 kGauss 
or higher, superior soft magnetic characteristics and extremely low 
magnetostriction 
Fourth Embodiment 
As a fourth embodiment, soft magnetic alloy films having compositions as 
shown in Table 3 were formed by the method of the present invention. These 
soft magnetic alloy films had a compositionally modulated wavelength 
.lambda. of 20 nm. In the preparation of these soft magnetic alloy films, 
the nitrogen gas partial pressure ratio Pn was selected to range between 5 
and 15%, and the high-temperature heat treatment was conducted at a 
heat-treating temperature of 400.degree. to 650.degree. C. in a magnetic 
field of 400 Oe. All the compositionally modulated nitride alloy films of 
the fourth embodiment showed excellent corrosion- and wear-resistances. 
The magnetic characteristics of these alloy films of the fourth embodiment 
are shown in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Saturation 
Mean Composition of 
magnetization 
Coercive force 
Sample 
film 4.eta.Ms 
Hc 
Nos. 
(atom %) (kG) (Hc) 
__________________________________________________________________________ 
Examples 
16 Fe.sub.72 Nb.sub.7 Si.sub.2 B.sub.9 N.sub.10 
12.4 0.6 
of 17 Fe.sub.74 Nb.sub.7 Si.sub.3 B.sub.10 N.sub.6 
12 0.7 
Embodiment 
18 Fe.sub.73 Nb.sub.6 Bl.sub.4 N.sub.8 
13.6 0.9 
19 Fe.sub.77 Nb.sub.4 B.sub.6 N.sub.13 
15 0.7 
20 Fe.sub.72 Nb.sub.5 Ta.sub.2 Si.sub.2 B.sub.9 N.sub.10 
12 0.7 
21 Fe.sub.72 Nba.sub.7 Si.sub.2 B.sub.9 N.sub.10 
11.8 0.7 
22 Fe.sub.79 Ta.sub.3 B.sub.7 N.sub.11 
16.3 0.3 
23 Fe.sub.76 Zr.sub.4 B.sub.7 N.sub.13 
15 0.6 
24 Fe.sub.70 Ti.sub.6 B.sub.14 N.sub.10 
12 0.8 
25 Fe.sub.69 Co.sub.4 Nb.sub.6 Si.sub.2 B.sub.9 N.sub.10 
14 0.7 
26 Fe.sub.68 Ni.sub.4 Nb.sub.7 Si.sub.2 B.sub.9 N.sub.10 
10.7 0.6 
27 Fe.sub.71 Co.sub.1 Ni.sub.1 Nb.sub.7 Si.sub.2 B.sub.9 N.sub.9 
12 0.6 
28 Fe.sub.73 Nb.sub.8 Si.sub.11 N8 
12 0.7 
__________________________________________________________________________ 
As will be seen from Table 3, all the samples Nos. 16 to 28 of the 
compositionally modulated nitride alloy films in accordance with the 
fourth embodiment exhibit high level of saturation magnetization and low 
level of coercive force, thus proving excellency as the soft magnetic 
alloy films. The mean compositions of the soft magnetic alloy films shown 
in Table 3 contain Fe as a main component and essentially includes N, at 
least one metal elements selected from the group consisting of Nb, Ta, Zr 
and Ti and at least one metalloid element selected from the group 
consisting of B and Si. As in the cases of Sample Nos. 25 to 27, Fe may be 
partially replaced by Co or Ni, provided that Fe remains to be the main 
constituent. It is also possible to replace Si as the metalloid element by 
Co which exhibits properties similar to those of Si and which has greater 
affinity to nitrogen than to Fe. 
As will be understood from the description of the fourth embodiment, the 
soft magnetic alloy film of the present invention can exhibit excellent 
soft magnetic characteristics and high levels of saturation magnetization 
over a wide variety of the alloy composition. The soft magnetic alloy 
films of the fourth embodiment did not show any generation of rust even 
after 24-hours immersion in pure water and small wear volume as measured 
as measured through a test conducted on an actual VCR tape running means 
using a metal tape, thus proving superiority both in corrosion resistance 
and wear resistance. It was also confirmed that the soft magnetic alloys 
in accordance with the fourth embodiment, after a high-temperature heat 
treatment, exhibited film structures composed of a nitride layer rich in 
both nitrogen and metalloid elements and a non-nitride layer poor in 
nitrogen and metalloid elements and containing fine crystal grains of Fe 
based alloy. 
As has been described, the soft magnetic alloy films in accordance with the 
fourth embodiments of the present invention exhibit superior soft magnetic 
characteristics, high levels of saturation magnetization, low 
magnetostriction and high thermal stability which prevents the soft 
magnetic characteristics from being impaired by high-temperature heat 
treatment, as well as excellent corrosion resistance and wear resistance. 
Fifth Embodiment 
Table 4 shows magnetic characteristics of soft magnetic alloy films formed 
as fifth embodiment of the invention by the method of the present 
invention. The formation of the compositionally modulated nitride alloy 
film was conducted such that a compositionally modulated wavelength 
.lambda. is 20 nm, with the nitrogen gas partial pressure ratio Pn being 
selected to range between 5 and 20%. The high-temperature heat treatment 
was conducted at a temperature between 400.degree. and 650.degree. C. in a 
magnetic field of 400 Oe. 
TABLE 4 
__________________________________________________________________________ 
Saturation 
magnetization 
Coercive force 
Sample 
Target Composition 
4.eta.Ms 
Hc 
Nos. 
(atom %) (kG) (Oe) 
__________________________________________________________________________ 
Examples 
29 Fe.sub.76 Nb.sub.9 Si.sub.3 B.sub.12 
12 0.4 
of 30 Fe.sub.76 Nb.sub.7.5 Si.sub.12 B.sub.5.5 
11.5 0.7 
Embodiment 
31 Fe.sub.85 Nb.sub.5 Si.sub.2 B.sub.8 
15.5 0.3 
32 Fe.sub.88 Nb.sub.4 B.sub.8 
15.8 0.9 
33 Fe.sub.88 Nb.sub.2 B.sub.10 
16.2 1 
34 Fe.sub.88 Ta.sub.4 B.sub.8 
16.3 0.3 
35 Fe.sub.84 Ta.sub.8 B.sub.8 
14 0.3 
36 Fe.sub.87 Zr.sub.5 B.sub.8 
15 0.6 
37 Fe.sub.78 Ti.sub.7 B.sub.15 
12 0.8 
38 Fe.sub.70 Co.sub.8 Nb.sub.6 Si.sub.4 B.sub.12 
15 0.7 
39 Fe.sub.80 Nb.sub.8 Si.sub.12 
12 0.7 
__________________________________________________________________________ 
As will be seen from Table 4, all the sample Nos. 29 to 39 of the soft 
magnetic alloy films produced in accordance with the method of the 
invention exhibit high levels of saturation magnetization and low levels 
of coercive force. The sample No. 38 of the soft magnetic alloy film 
contains Co. Superior soft magnetic characteristics are obtainable even 
when a part of Fe is replaced by Co or Ni or the like provided that Fe 
remains the main constituent. All of the soft magnetic alloy films shown 
in Table 4 contain N, at least one metal element selected from the group 
consisting of Nb, Ta, Zr and Ti and at least one metalloid element 
selected from the group consisting of B and Si. Si as the metalloid 
element may be replaced by C which exhibits similar properties to those of 
Si and which has a greater affinity to nitrogen than to Fe. 
As will be understood from the description of the fifth embodiment, the 
method of the present invention for producing a soft magnetic alloy film 
enables production of soft magnetic alloy films having both superior soft 
magnetic characteristics and high levels of saturation magnetization, over 
a wide range of composition. The soft magnetic alloy films of the fifth 
embodiment did not show any generation of rust even after 24-hours 
immersion in pure water and small wear volume as measured through a test 
conducted on actual VCR tape running using a metal tape, thus proving 
superiority both in corrosion resistance and wear resistance. It was also 
confirmed that the soft magnetic alloys in accordance with the fourth 
embodiment, after a high-temperature heat treatment, exhibited film 
structures composed of a nitride layer rich in nitrogen and metalloid 
elements and a non-nitride layer poor in nitrogen and metalloid elements 
and containing fine crystal grains of Fe based alloy. 
As has been described, the soft magnetic alloy films produced by the method 
of the present invention exhibit superior soft magnetic characteristics 
and high level of magnetic saturation over a wide range of composition.