Rare earth metal-iron group metal target, alloy powder therefor and method of producing same

A rare earth metal-iron group metal target for a magneto-optical disk is produced by mixing powder (a) produced by the rapid quenching treatment of an alloy composed of at least one rare earth metal and at least one iron group metal in a composition range which permits the formation of an eutectic structure, with powder (b) from at least one iron group metal in an amount necessary for meeting the composition requirements of the target; and subjecting the resulting mixture to pressure sintering in vacuum or in an inert gas atmosphere at a temperature lower than a liquid phase-appearing temperature of the mixture to produce a rare earth metal-iron group metal intermetallic bonding layer between the particles.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be explained in detail. FIGS. 1(a), (b) and (c) 
show the microstructures of the target of the present invention. Their 
magnifications are 100 for FIG. 1(a), x200 for FIG. 1 (b) and x1000 for 
FIG. 1(c). Their electron probe microanalysis (EPMA) has confirmed that an 
iron group metal phase such as Fe phase and a rare earth metal-iron group 
metal eutectic alloy phase are bonded with each other via a solid phase 
diffusion bonding layer consisting essentially of an inter metallic 
compound of the rare earth metal and the iron group metal. 
The characteristics of the structure of the target of the present invention 
will be explained referring to FIG. 1. 
The first characteristic is that an Tb-Fe eutectic alloy phase is composed 
of an Fe Tb precipitation phase and an .alpha.-Tb precipitation phase both 
extremely uniformly and finely dispersed. This is due to the fact that 
alloy powder produced by a rapid quenching treatment such as an atomizing 
method and structure in which an .alpha.-Tb precipitation phase and an 
Fe:Tb precipitation phase are uniformly and finely precipitated is used as 
a starting material, and that pressure sintering is conducted at a 
temperature lower than a liquid phase-appearing temperature to retain this 
structure. 
According to the present invention, the distance between the adjacent 
precipitation phases of the same type (both .alpha.-Tb or both Fe:Tb ) is 
5.mu.m or less on average in a uniform dispersion state. 
Because the target of the present invention has the above uniform fine 
structure, the difference in composition between the target used and the 
thin film produced therefrom by sputtering can be extremely reduced, 
thereby decreasing the time of presputtering conducted before the 
sputtering. 
According to the article in Summary of Lectures held in 10th Academic 
Meeting of Japan Magnetics Association (p.128, 1986), when a composite 
target, namely a target composed of a rare earth metal and an iron group 
metal is used for sputtering, the iron group metal is more inclined to be 
sputtered at the target periphery than the rare earth metal, resulting in 
a thin layer composition poor in the iron group metal. On the other hand, 
in a case of the target composed of intermetallic compounds, the rare 
earth metal is more inclined to be sputtered at the target periphery side 
than the iron group metal, resulting in a thin layer composition rich in 
the iron group metal. On the contrary, in the target of the present 
invention, a eutectic alloy phase composed of an .alpha.-phase of a rare 
earth metal and a rare earth metal-iron group metal intermetallic 
compound, a solid phase bonding layer and an iron group metal phase are 
uniformly and finely dispersed, so that the difference in a sputtering 
direction between rare earth metal particles and the iron group metal 
particles is reduced, resulting in a small composition unevenness. 
The reasons for decreasing the presputtering time are considered as 
follows: (1) Compared with the difference in sputtering rate between iron 
group metals and rare earth metals as shown in Japanese Patent Laid-Open 
No.62-70550, the difference in the sputtering rate between the iron group 
metals and rare earth metal-iron group metal intermetallic compounds is 
smaller; and 
(2) Rare earth metal-iron group metal alloy powder is produced by rapid 
quenching, the .alpha.-phase of rare earth metal and the intermetallic 
compound phase are uniformly and finely dispersed; in other words, the 
rare earth metal phase are finely precipitated, and so the sputtering rate 
of the e-phase of rare earth metal is increased as a whole nearly to the 
level of the intermetallic compound phase, despite the fact that the 
sputtering rate of rare earth metal does not change microscopically. 
The second characteristic of the structure of the target of the present 
invention is that it has an extremely thin diffusion bonding layer 
consisting essentially of the rare earth metal-iron group metal 
intermetallic compound. This is due to the fact that the bonding layer is 
a solid phase diffusion bonding layer formed by pressure sintering at a 
temperature lower than a liquid phase appearing temperature. 
Since the diffusion bonding layer is thin, providing the structure with 
substantially no unevenness, stable thin layer characteristics can be 
obtained even with a long sputtering time, without suffering from the 
deterioration of mechanical strength. 
According to the present invention, this bonding layer can be adjusted to 
be as thin as 10.mu.m or less, but from the aspect of mechanical strength, 
it is desirably adjusted to 30.mu.m or less. 
The rare earth metals which will be used in the target of the present 
invention include at least one of Tb, Gd, Dy, Nd, Sm, Ho, Tm, etc. When 
the content of the rare earth metal is lower than 15 atomic % or exceeds 
45 atomic %, it is difficult to provide a thin layer capable of 
functioning as a magneto-optical recording medium, so that it should be in 
the range of 15-45 atomic %. 
With respect to the iron group metals, they are at least one of Fe, Co and 
Ni. 
Thus, the intermetallic compounds mentioned herein include not only Fe:Tb, 
for instance, but also intermetallic compounds of various types of iron 
group metals and rare earth metals such as FeCoTb. 
When the alloy is used as a recording medium, its life as a medium and 
particularly its corrosion resistance are important together with its 
magnetic properties. However, since the rare earth metal has a strong 
affinity to oxygen, it is selectively oxidized by the water permeating 
into the target through a substrate and a protective layer during its use 
as a recording medium for a long period of time, resulting in the 
deterioration of the magnetic properties thereof. 
Effective against this problem is to add Ti, Al, Cu, Cr, Nb, Ta, Pd or Pt 
to the target. Thus an additional characteristic of the present invention 
is that the target may contain at least one element selected from the 
group consisting of Ti, Al, Cu, Cr, Nb, Ta, Pb and Pt. Incidentally, since 
excess addition of one or more of the above elements adversely affects the 
magnetic properties of the resulting thin film, it should be 15 atomic % 
or less based on the total amount of the target. 
FIG. 2 shows the microstructure of an Fe-Co-Dy target according to another 
embodiment of the present invention. It has been confirmed that it has a 
structure in which an iron group metal phase consisting of Fe and Co and a 
eutectic alloy phase consisting of an Fe-Dy intermetallic compound and 
.alpha.-Dy are bonded with each other via a diffusion bonding layer 
consisting essentially of an Fe-Dy intermetallic compound. 
Next, the methods of producing the target of the present invention and 
alloy powder therefor will be explained. 
In the present invention, first, rare earth alloy-iron group metal alloy 
powder and iron group metal powder are prepared. One of the 
characteristics of the present invention is that the rare earth metal-iron 
group metal alloy powder is produced by a rapid quenching treatment, and 
that this rapid quenching treatment enables the resulting alloy powder to 
have an .alpha.-phase of the rare earth metal and the intermetallic 
compound phase which are uniform and finely dispersed on the powder level, 
that is, within each particle. Accordingly, from the aspect of 
composition, it is necessary that the composition of the rare earth metal 
and the iron group metal is within the composition range which enables the 
formation of a eutectic structure. 
The rare earth metal-iron group metal alloy powder can be obtained by 
melting starting materials and then conducting a rapid quenching treatment 
thereof, and the starting materials to be melted desirably consist 
essentially of a low-oxygen rare earth metal-iron group metal eutectic 
alloy. 
Specifically speaking, although it is possible to use as starting materials 
to be melted pure rare earth metal and iron group metal in a predetermined 
proportion, the pure rare earth metal has a high oxygen content; for 
instance commercially available high-pure Tb contains 900-1200 ppm of 
oxygen. And the materials cannot be melted completely without heating at 
high temperature for a long time, so that the resulting rare earth 
metal-iron group metal alloy powder inevitably has an increased oxygen 
content, for instance, 2200 ppm for Tb-Fe alloy powder. 
On the contrary, a rare earth metal-iron group metal eutectic alloy 
produced by a fused salt electrolysis method, etc. as low an oxygen 
content as 100-500 ppm, and the melting temperature is relatively low. 
Accordingly, it is possible to decrease the melting time and so to reduce 
the oxygen content. 
Applicable as a rapid quenching method are an inert gas atomizing method, a 
vacuum atomizing method, a roll quenching method, etc. which use an alloy 
melt, and a rotating electrode method using an electrode in the range of 
the above composition range. In a water-cooled roll quenching method and a 
rotating electrode method, etc, the atmosphere should be vacuum or an 
inert gas to prevent the oxidation of the alloy. 
FIG. 3 shows the microstructure of Fe-Tb alloy powder produced by gas 
atomizing, in which .alpha.-Tb and Fe:Tb are uniformly and finely 
precipitated. 
Since rare earth metal-iron group metal alloy powder has a significantly 
greater oxidation resistance than pure rare earth metal powder, the target 
produced from the above alloy powder has an oxygen content lower by 
500-1000 ppm or even more than that produced by sintering a mixture of 
rare earth metal powder and iron group metal powder. 
The starting material powder has desirably an average partial size of 1 mm 
or less. When the average particle size exceeds 1 mm, unevenness appears 
in the resulting sintered body, so that the use thereof as a target 
provides a thin film with a partially uneven composition. 
Incidentally, Ti, Al, Cu, Cr, Nb, Ta, Pd or Pt as a corrosion 
resistance-improving element may be added alone or in the form of an alloy 
with iron group metal such as Fe-Nb, Fe-Cr, etc., to the rare earth 
metal-iron group metal alloy powder and the iron group metal powder 
produced by a rapid quenching treatment. 
After mixing the above starting material powder, pressure sintering is 
conducted at a temperature lower than a liquid phase-appearing 
temperature. The reasons for conducting the pressure sintering at a 
temperature lower than the liquid phase-appearing temperature are that if 
the pressure sintering temperature is equal to or higher than the liquid 
phase-appearing temperature, the bonding layer between the iron group 
metal phase and the rare earth metal-iron group metal eutectic alloy phase 
grows abnormally, reducing the mechanical strength of the sintered body, 
and that the .alpha.-phase of rare earth metal precipitated in the 
eutectic alloy phase consisting of rare earth metal and iron group metal 
disappears by reaction with the iron group metal. The preferred pressure 
sintering temperature is lower than the liquid phase-appearing temperature 
and higher than or equal to a temperature below the liquid phase appearing 
temperature by 100.degree. C., and more preferably it is lower than the 
liquid-phase appearing temperature and higher than or equal to a 
temperature below the liquid phase-appearing temperature by 30.degree. C. 
Typical examples of the liquid phase- appearing temperature are 
840.degree. C. for Tb-Fe, 695.degree. C. for Tb-Fe-Co, and 630.degree. C. 
for Tb-Gd-Fe. 
As mentioned above, the pressure sintering at temperatures lower than the 
above liquid phase-appearing temperature can achieve the formation of 
extremely thin bonding layer, and further it provides the following 
effects: 
(1) It is easy to maintain and control the amounts of an .alpha.-phase of 
rare earth metal and an intermetallic compound in alloy powder obtained as 
starting material powder, and their good dispersion state, 
(2) the resulting structure has substantially no unevenness, and 
(3) the oxygen content can be maintained at a low level, thereby 
contributing to the stabilization of thin film characteristics in the 
sputtering for a long period of time. 
The pressure sintering can be conducted by hot isostatic pressing (HIP), 
hot pressing, hot pack rolling, hot pack forging, etc. As for specific 
conditions, in the case of hot isostatic pressing, with the conditions of 
the heating temperature lower than a liquid phase-appearing temperature 
and higher than or equal to a temperature which is lower than the liquid 
phase-appearing temperature by 30.degree. C. and an inert gas pressure of 
1000-1500 atms. for 2-3 hours, the thickness of the diffusion bonding 
layer between the iron group metal phase and the rare earth metal-iron 
group metal eutectic alloy phase can be controlled within 10-30 .mu.m, and 
the density of the sintered body can be made as high as 97% or more. 
In the case of hot pressing to provide a sintered body having a density of 
95% or more, it is desirably conducted at a heating temperature lower than 
the liquid phase-appearing temperature and higher than or equal to a 
temperature which is lower than liquid phase-appearing temperature by 
30.degree. C. and pressing pressure of 150kg/cm.sup.2 or more for 2 hours 
or so. 
For hot pack rolling and hot pack forging, the heating temperature may be 
the same as in HIP, but it is necessary that a rolling or forging 
reduction in each pass be within 10%. 
EXAMPLE 1. 
Experiments were conducted by using the compositions and sintering 
conditions as shown in Table 1. In all samples, powder having an average 
particle size of 0.3 mm or less was used. With respect to the production 
of powder, the Tb-Fe powder of the present invention (Sample Nos. 1-6) was 
produced by adding Fe or Tb to a low-oxygen alloy (oxygen content:130 ppm) 
having a composition of 70.2 at. % Tb-Fe produced by a fused salt 
electrolysis method to achieve the desired composition, introducing it 
into a crucible equipped with a melt discharging nozzle at the bottom 
thereof, placing the crucible in a gas atomizing apparatus, evacuating the 
apparatus to a level of 10.sup.-3 -10.sup.-4 Torr, melting the alloy in 
the crucible by heating by high frequency induction (the starting material 
powder is completely melted when the temperature reaches about 
1200.degree. C.), and then conducting gas atomizing of the alloy by 
opening the discharging nozzle while applying Ar gas pressure. The Tb-Fe 
powder produced by the above method contained about 1200 ppm of oxygen on 
average. 
Nd-Dy-Fe powder, Fe powder, Co powder, and Fe-Co powder were also produced 
by argon gas atomizing like the Tb-Fe powder. An average oxygen content in 
the resulting powder was 1500 ppm for Nd-Dy-Fe, 250 ppm for Fe; 80 ppm for 
Co, and 70 ppm for Fe-Co. 
Each gas-atomized powder of the above rare earth metal-iron group metal 
alloy and the iron group metal was mixed in a composition as shown in 
Table 1, and charged into a V-type mixer, which was evacuated and then 
filled with an Ar gas to prevent the oxidation of the mixed powder. Mixing 
of the powder was conducted at a cumulative rotation of 6000 or more to 
provide as uniform powder mixture as possible. 
The mixed powder was then charged into a capsule constituted by a 3 
mm-thick mild steel sheet, and the capsule was evacuated to 10.sup.-4 Torr 
or more, and heated at 400.degree. C. After the capsule was heated at 
400.degree. C. for 5 hours, it was sealed. Each capsule was subjected to 
pressure sintering by using a hot isostatic press (HIP) under the 
conditions as shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Sample 
Mixture Composition (at %) 
Powder Composition 
Sintering Conditions 
No..sup.1 
Tb Nd Dy Fe Co 
(at %) Temp. (.degree.C.) 
Pressure (atm.) 
Time (hour) 
__________________________________________________________________________ 
1 22 -- -- 68 10 
58Tb--Fe Powder, Fe 
685 1200 2 
Powder, Co Powder 
2 25 -- -- 65 10 
58Tb--Fe Powder, Fe 
685 1200 2 
Powder, Co Powder 
3 28 -- -- 62 10 
58Tb--Fe Powder, Fe 
685 1200 2 
Powder, Co Powder 
4 25 -- -- 65 10 
45Tb--Fe Powder, Fe 
685 1200 2 
Powder, Co Powder 
5 25 -- -- 65 10 
85Tb--Fe Powder, Fe 
685 1200 2 
Powder, Co Powder 
6 25 -- -- 65 10 
58Tb--Fe Powder, 
685 1200 2 
82.4Fe--Co Powder 
7 -- 13 26 46 15 
19Nd--38Dy--Fe Powder, 
560 1200 2 
Fe Powder, Co Powder 
.sup. 8.sup.2 
25 -- -- 65 10 
-- -- -- -- 
.sup. 9.sup.3 
25 -- -- 65 10 
25Tb--65Fe--10Co 
1100 150 2 
10.sup.4 
25 -- -- 65 10 
Tb Powder, Fe Powder 
685 150 2 
Co Powder 
11.sup.5 
25 -- -- 65 10 
38Tb--Fe Powder, 
1250 1 2 
Fe Powder, Co Powder 
12.sup.6 
25 -- -- 65 10 
Tb Powder, Fe Powder 
685 150 2 
Co Powder 
__________________________________________________________________________ 
Note: 
.sup.1 Sample Nos. 1-7: Present Invention Sample Nos. 8-12: Comparative 
Example 
.sup.2 "Nikkei New Material," P. 61, November 24, 1986 
.sup.3 Japanese Patent LaidOpen No. 6191336 
.sup.4 Japanese Patent LaidOpen No. 6199640 
.sup.5 Japanese Patent LaidOpen No. 60230903 
.sup.6 Japanese Patent LaidOpen No. 6270550 
After completion of the sintering, and after iron skin was removed from the 
sintered body by a lathe and a surface grinder, each target of 101 mm in 
diameter and 3 mm in thickness for evaluating thin film characteristics, 
each specimen for measuring deflection strength and each sample for 
analyzing an oxygen content were prepared. 
With respect to Comparative Examples, Sample No. 8 is a target produced by 
vacuum melting and vacuum casting method by using a calcia crucible 
("Nikkei New Material", p.61, Nov. 24, 1986), and Sample Nos.9-12 are 
those produced by sintering by a hot press apparatus under the conditions 
indicated by the references shown in the note of Table 1. Among them, 
Sample No. 12 was, after pressure sintering, heated at 800.degree. C. for 
10 minutes by high frequency induction and then cooled by blowing an Ar 
gas. 
Evaluation of the resulting thin layer was conducted by forming a thin 
layer of 0.1 .mu.m in thickness on a 7059 glass of 0.15mm in thickness 
manufactured by Corning by means of a magnetron-type sputtering apparatus 
having a high frequency source. The conditions of forming the thin layer 
were high frequency output of 400 W, and Ar gas pressure of 
5.times.10.sup.-3 Torr, distance of 70 mm between the target and the glass 
substrate, and during the formation of the thin layer, the glass substrate 
was not rotated in opposition to the target. 
Table 2 shows the oxygen contents and deflection strength of the targets of 
the present invention and of Comparative Examples, and the compositions of 
thin films formed from such targets. Each of the targets of the present 
invention has an oxygen content of 1100 ppm or less and good deflection 
strength of 10kg/cm.sup.2 or more. The reason for such a good deflection 
strength appears to be the effect of the iron group metal phase existing 
in the target. 
And with respect to thin film composition, it is only 2 atomic % or less 
richer in the iron group metal than the target composition, while the 
targets of Comparative Examples have problems in one or more of the 
following characteristics: oxygen content, deflection strength and thin 
film composition. 
TABLE 2 
__________________________________________________________________________ 
Oxygen Content 
Deflection Strength 
Thin Layer Composition (at %) 
Sample No..sup.1 
(ppm) (Kg/cm.sup.2) 
Tb Nd Dy Fe Co 
__________________________________________________________________________ 
1 920 12 21.1 
-- -- 69.6 
9.3 
2 1010 10 24.2 
-- -- 66.4 
9.4 
3 1090 11 27.4 
-- -- 63.3 
9.3 
4 890 12 23.5 
-- -- 67.0 
9.5 
5 1100 10 24.7 
-- -- 66.0 
9.3 
6 980 10 24.3 
-- -- 65.8 
9.9 
7 1498 21 -- 12.3 
24.7 
48.6 
14.2 
8 300 2 16.3 
-- -- 73.4 
10.3 
9 580 2 16.2 
-- -- 73.2 
10.1 
10 1800 15 27.2 
-- -- 61.8 
11.0 
11 1700 6 16.3 
-- -- 73.3 
9.8 
12 2100 5 22.9 
-- -- 67.5 
9.6 
__________________________________________________________________________ 
Note: 
.sup.1 Sample Nos. 1-7: Present invention Sample Nos. 8-12: Comparative 
Example 
FIG. 4 shows the relations between a thin film composition and sputtering 
time in the case of forming a thin layer by using the targets of the 
present invention and those of Comparative Examples. In the case of the 
target of the present invention (Sample No. 2), only 1 atomic % of change 
in Tb content occurs until the thin layer composition becomes stable from 
the initiation of sputtering, and the time necessary for the thin layer 
composition to become stable is as short as within 4 hours. On the other 
hand, in the case of a target produced by sintering a mixture of pure Tb 
powder, Fe powder and Co powder (Comparative Example 10), the Tb content 
decreases by nearly 3 atomic % until it is stabilized, and it took 10 
hours or more until the composition became stable. With respect to the 
targets of Comparative Examples 8, 9 and 11, their thin layer compositions 
were stable from the initiation of sputtering, but they were poor in Tb by 
9 atomic % as compared with the target compositions. In Comparative 
Example 12, the thin layer composition lacked stability and was poor in Tb 
by nearly 2-3 atomic % compared to the target composition. 
FIG. 5 shows the distribution of Tb in the plane of the thin layer. In a 
thin layer formed by using the target of the present invention, its Tb 
content is -0.8 atomic % at a center and -0-0.2 atomic % at the periphery 
compared with the target composition, while much larger differences were 
observed in Comparative Examples. 
EXAMPLE 2 
Samples having compositions as shown in Table 3 were sintered under 
conditions as shown in Table 3. In all of the samples, powder of an 
average particle size of 0.3 mm or less was used to have the desired 
composition, and mixed uniformly in a V-type mixer to provide mixed 
powder. The resulting mixed powder was charged into a die of 125 mm in 
diameter and pressed at room temperature, and sintered by hot pressing in 
a carbon mold. The production of starting materials per se were conducted 
in the same manner as in Example 1. 
The oxygen content and deflection strength of the resulting targets and the 
compositions of the thin layers formed from such targets are shown in 
Table 4. 
TABLE 3 
__________________________________________________________________________ 
Sample 
Mixture Composition (at %) 
Powder Composition 
Sintering Conditions 
No..sup.1 
Tb Dy Fe Co (at %) Temp. (.degree.C.) 
Pressure (atm.) 
Time (hour) 
__________________________________________________________________________ 
13 28.0 
-- 72.0 
-- 72Tb--28Fe Alloy Powder + 
830 150 2 
Fe Powder 
14 28.0 
-- 72.0 
-- 82Tb--18Fe Alloy Powder + 
830 150 2 
Fe Powder 
15 28.0 
-- 72.0 
-- 95Tb--5Fe Alloy Powder + 
830 150 2 
Fe Powder 
16 28.0 
-- 67.0 
5.0 
72Tb--28Fe Alloy Powder + 
685 150 2 
Fe Powder, Co Powder 
17 -- 27.5 
72.5 
-- 71.5Dy--28.5Fe Alloy Powder + 
880 150 2 
Fe Powder 
18 -- 27.5 
72.5 
-- 82Dy--18Fe Alloy Powder + 
880 150 2 
Fe Powder 
19 -- 27.5 
72.5 
-- 94Dy--6Fe Alloy Powder + 
880 150 2 
Fe Powder 
20 -- 27.6 
67.3 
5.1 
71.5Dy--28.5Fe Alloy Powder + 
720 150 2 
Fe Powder, Co Powder 
21 28.0 
-- 72.0 
-- 28.0Tb--72.0Fe Alloy powder 
1100 150 2 
22 28.0 
-- 72.0 
-- Tb Powder + Fe Powder 
830 150 2 
23 28.0 
-- 67.0 
5.0 
Tb Powder + Fe Powder + 
685 150 2 
Co Powder 
24 -- 27.6 
67.3 
5.1 
27.6Dy--67.3Fe--5.1 Co 
1100 150 2 
Alloy Powder 
__________________________________________________________________________ 
Note: 
.sup.1 Sample Nos. 13-20: Present Invention Sample Nos. 21-24: Comparativ 
Example 
TABLE 4 
__________________________________________________________________________ 
Oxygen Content 
Deflection Strength 
Thin Layer Composition (at %) 
Sample No..sup.1 
(ppm) (Kg/cm.sup.2) 
Tb Dy Fe Co 
__________________________________________________________________________ 
13 980 8 25.8 
-- 74.2 
-- 
14 1230 9 27.0 
-- 73.0 
-- 
15 1500 10 27.4 
-- 72.6 
-- 
16 940 9 26.3 
-- 68.9 
4.8 
17 1000 9 -- 25.3 
74.7 
-- 
18 1300 10 -- 26.7 
73.7 
-- 
19 1470 9 -- 27.0 
73.0 
-- 
20 990 9 -- 25.9 
68.8 
5.3 
21 1000 2 22.3 
-- 77.7 
-- 
22 2000 10 30.6 
-- 69.4 
-- 
23 2100 10 30.3 
-- 64.2 
5.5 
24 900 2 -- 22.9 
72.2 
4.9 
__________________________________________________________________________ 
Note: 
.sup.1 Sample Nos. 13-20: Present Invention Sample Nos. 21-24: Comparativ 
Example 
All of the targets of the present invention show as small oxygen content as 
1500 ppm or less and good deflection strength and were about 2-3 % richer 
in iron group metal than the target compositions. On the other hand, the 
targets of Comparative Examples had problems in oxygen content, deflection 
strength and/or thin layer composition. 
EXAMPLE 3 
With Sample No. 4 (present invention) and Sample No. 12 (Comparative 
Example) prepared in Example 1, thin layers were formed in the same manner 
as in Example 1, and their magnetic anisotropy constant Ku (J/m.sup.3) was 
measured by a torque meter. 
FIG. 6 (a) shows the relation between the magnetic anisotropy constant Ku 
(J/m.sup.3) of the thin layer formed by using Sample No. 4 (present 
invention) and cumulative sputtering time. And FIG. 6(b) shows the 
relations between the magnetic anisotropy constant Ku (J/m.sup.3) of the 
thin layer formed by using Sample No. 12 (Comparative Example) and 
cumulative sputtering time. 
In the target of the present invention, the magnetic anisotropy constant 
became stable after the cumulative sputtering time lapsed 4 hours, while 
in Sample No. 12 having a large oxygen content (Comparative Example) the 
magnetic anisotropy was unstable, with Ku decreasing substantially, 
meaning that the resulting thin layer behaves as if it were a horizontally 
magnetized layer. 
EXAMPLE 4 
Fe powder, Co powder, Fe-Co powder, Fe-Nb powder, Fe-Co-Nb powder, Fe-Pt 
powder and Fe-Co-Nb-Pt powder produced by Argon gas atomizing in the same 
manner as in Example 1 were used in compositions as shown in Table 5 to 
provide each powder mixture which was then subjected to a HIP treatment at 
685.degree. C., 1200 atms. for 2 hours in the same manner as in Example 1 
and then sputtered. 
The oxygen content and deflection strength of each target and the 
composition of a thin layer produced from each target are shown in Table 
6. Table 6 shows that all of them had a low oxygen content of 1100 ppm or 
less and a good deflection strength of 10kg/cm.sup.2 or more. And with 
respect to a thin layer composition, the contents of corrosion-resistant 
elements in the thin layer were substantially the same as in the target 
compositions. 
TABLE 5 
__________________________________________________________________________ 
Sample 
Mixture Composition (at %) 
Powder Composition 
No. Tb Fe 
Co Nb Pt (at %) 
__________________________________________________________________________ 
25 24 63 
11 2 -- 58.4Tb--Fe, Fe, Co, Nb 
26 24 63 
11 2 -- 58.4Tb--Fe, Fe--19.33Nb, Nb 
27 24 63 
11 2 -- 58.4Tb--Fe, Fe--11.66Nb, Fe, Co 
28 24 63 
11 2 -- 58.4Tb--Fe, Fe--18.68Co--3.4Nb 
29 24 56 
10 2 8 58.4Tb--Fe, Fe, Co, Nb, Pt 
30 24 56 
10 2 8 58.4Tb--Fe, Fe--11.66Nb, Fe, Co, Pt 
31 24 56 
10 2 8 58.4Tb--Fe, Fe--11.66Nb, Fe--10.93Pt, Fe, Co 
32 24 56 
10 2 8 58.4Tb--Fe, Fe--16.96Co--3.39Nb--13.57Pt 
33 24 63 
10 2Ti 
-- 58.4Tb--Fe, Fe, Co, Ti 
34 24 63 
10 2Al 
-- 58.4Tb--Fe, Fe, Co, Al 
35 24 63 
10 2Cr 
-- 58.4Tb--Fe, Fe, Co, Cr 
36 24 63 
10 2Ta 58.4Tb--Fe, Fe, Co, Ta 
37 24 63 
10 2Pd 58.4Tb--Fe, Fe, Co, Pd 
__________________________________________________________________________ 
Note: 
All Samples: Present invention 
TABLE 6 
__________________________________________________________________________ 
Oxygen Content 
Deflection Strength 
Thin Layer Composition (at %) 
Sample No..sup.1 
(ppm) (Kg/cm.sup.2) 
Tb Fe Co Nb 
Pt 
__________________________________________________________________________ 
25 1100 11 23.2 
63.3 
11.2 
2.3 
-- 
26 1030 12 23.3 
63.2 
11.4 
2.1 
-- 
27 990 12 23.2 
63.6 
11.2 
2.0 
-- 
28 980 10.5 23.4 
63.4 
11.1 
2.1 
-- 
29 940 11 23.4 
55.6 
10.4 
2.2 
8.4 
30 960 12 23.2 
56.1 
10.3 
2.1 
8.3 
31 910 12 23.1 
56.5 
10.3 
2.0 
8.1 
32 870 12 23.3 
56.5 
10.1 
2.0 
8.1 
33 930 11 23.2 
63.1 
11.3 
2.4 
-- 
34 970 12 23.2 
63.3 
11.2 
2.3 
-- 
35 960 10.5 23.3 
63.4 
11.3 
2.0 
-- 
36 980 11 23.4 
63.3 
11.2 
2.1 
-- 
37 1010 12 23.5 
63.2 
11.1 
2.2 
-- 
__________________________________________________________________________ 
Note: 
.sup.1 All samples: Present invention 
Next, the thin film formed on the glass substrate was evaluated with 
respect to corrosion resistance. The sample used for evaluation was Sample 
No. 29 (present invention) and Sample No. 12 (Comparative Example), and 
the evaluation was carried out by placing the substrate formed with each 
thin layer in an environment at a temperature of 65.degree. C. and a 
relative humidity of 95%, and measuring its magnetic properties every 50 
hours. The results are shown in FIG. 7. 
It is clear from the Table that Sample No. 29 suffered from only a small 
change in magnetic property (coercive force Hc) over a long period of test 
time. On the other hand, Sample No. 12 underwent an extreme change in 
magnetic properties toward the Fe-rich side after the lapse of short time, 
and after the lapse of 200 hours in test, it lost magnetic characteristics 
as a vertically magnetized layer. 
The above phenomenon appears to be caused by the fact that Tb is 
preferentially oxidized so that the magnetic characteristics change toward 
the Fe side, resulting in the complete departure from an amorphous 
composition. 
As explained above in detail, by using as starting material powder a 
mixture of rare earth metal-iron group metal alloy powder in which an 
.alpha.-phase of rare earth metal and an intermetallic compound phase are 
finely precipitated and iron group metal alloy powder, and subjecting the 
resulting mixture to pressure sintering at a temperature lower than a 
liquid phase-appearing temperature, it is possible to suppress the oxygen 
content as low as 1500 ppm or less and to minimize the difference in 
composition between a target used and a thin layer formed, enabling the 
formation of a thin layer having a stable composition for a long period of 
sputtering time so that the control of a thin layer composition is easy. 
In addition, the target produced by such a method has excellent mechanical 
workability. Thus, the present invention has high commercial value. 
The present invention has been explained in detail referring to the 
Examples, but it should be noted that any modification can be possible 
unless it deviates from the scope of the present invention which is 
defined by the claims attached hereto.