U.S. patent application number 11/789422 was filed with the patent office on 2008-02-14 for fe-co based target material and method for producing the same.
This patent application is currently assigned to SANYO SPECIAL STEEL CO., LTD.. Invention is credited to Yoshikazu Aikawa, Akihiko Yanagitani.
Application Number | 20080038145 11/789422 |
Document ID | / |
Family ID | 38767425 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080038145 |
Kind Code |
A1 |
Yanagitani; Akihiko ; et
al. |
February 14, 2008 |
Fe-Co based target material and method for producing the same
Abstract
There is disclosed a method for producing a Fe--Co based target
material for forming a soft magnetic thin-film. This method
comprises the steps of: preparing a first raw-material powder
having an Fe:Co weight ratio ranging from 8:2 to 7:3 and a second
raw-material powder having an Fe--Co weight ratio ranging from 2:8
to 0:10; mixing the first raw-material powder and the second
raw-material powder together to obtain a powder mixture having an
Fe:Co weight ratio ranging from 8:2 to 2:8; and applying a pressure
of not less than 100 MPa to the powder mixture at a temperature
ranging from 1073 to 1473 K for consolidation. At least one
additional element selected from the group consisting of Nb, Zr, Ta
and Hf is added to either one or both of the first and second
raw-material powders in a total amount of 3 to 15 atom % with
respect to the total amount of the powder mixture. The Fe--Co based
target material thus produced has a high density, while having a
magnetic permeability lower than the conventional one.
Inventors: |
Yanagitani; Akihiko;
(Himeji-Shi, JP) ; Aikawa; Yoshikazu; (Himeji-Shi,
JP) |
Correspondence
Address: |
THE WEBB LAW FIRM, P.C.
700 KOPPERS BUILDING
436 SEVENTH AVENUE
PITTSBURGH
PA
15219
US
|
Assignee: |
SANYO SPECIAL STEEL CO.,
LTD.
Himeji-shi
JP
|
Family ID: |
38767425 |
Appl. No.: |
11/789422 |
Filed: |
April 24, 2007 |
Current U.S.
Class: |
420/125 ; 419/37;
420/127; 420/435 |
Current CPC
Class: |
B22F 2998/10 20130101;
C22C 38/10 20130101; C22C 38/14 20130101; B22F 2998/10 20130101;
C22C 1/0433 20130101; H01F 10/14 20130101; C23C 14/3414 20130101;
H01F 1/22 20130101; C22C 33/0257 20130101; B22F 3/15 20130101; B22F
1/0003 20130101; B22F 3/12 20130101; C22C 38/12 20130101; C22C
19/07 20130101; B22F 3/15 20130101; C22C 2202/02 20130101; H01F
41/0246 20130101; H01F 10/16 20130101 |
Class at
Publication: |
420/125 ;
419/037; 420/127; 420/435 |
International
Class: |
C22C 38/10 20060101
C22C038/10; B22F 1/00 20060101 B22F001/00; C22C 38/12 20060101
C22C038/12; C22C 38/14 20060101 C22C038/14; C22C 19/07 20060101
C22C019/07 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2006 |
JP |
2006-128224 |
Claims
1. A method for producing a Fe--Co based target material,
comprising the steps of: preparing a first raw-material powder
having an Fe:Co weight ratio ranging from 8:2 to 7:3 and a second
raw-material powder having an Fe--Co weight ratio ranging from 2:8
to 0:10; mixing the first raw-material powder and the second
raw-material powder together to obtain a powder mixture having an
Fe:Co weight ratio ranging from 8:2 to 2:8; and applying a pressure
of not less than 100 MPa to the powder mixture at a temperature
ranging from 1073 to 1473 K for consolidation, wherein at least one
additional element selected from the group consisting of Nb, Zr, Ta
and Hf is added to either one or both of the first and second
raw-material powders in a total amount of 3 to 15 atom % with
respect to the total amount of the powder mixture.
2. The method according to claim 1, wherein, prior to the mixing
step, the additional element is added to the first raw-material
powder in a total amount of not less than 1 atom % with respect to
the total amount of the first raw-material powder.
3. The method according to claim 1 or 2, wherein, prior to the
mixing step, the additional element is added to the second
raw-material powder in a total amount of not less than 1 atom %
with respect to the total amount of the second raw-material
powder.
4. An Fe--Co based target material, which is obtainable by the
method according to claim 1, wherein the Fe--Co based target
material is made of an Fe--Co based alloy comprising: 85 to 97 atom
% of Fe and Co, which have a Fe:Co weight ratio ranging from 8:2 to
2:8; and 3 to 15 atom % of at least one additional element selected
from the group consisting of Zr, Nb, Ta and Hf.
5. The Fe--Co based target material according to claim 4, having
magnetic permeability ranging from 10 to 200.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. 128224/2006 filed on May 2, 2006, the entire
disclosure of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates to a Fe--Co based target material for
forming a soft magnetic thin-film by a sputtering method, and a
method for producing the target material.
BACKGROUND ART
[0003] The recent progress in the magnetic recording technology is
remarkable, and the record densities of magnetic record media are
being heightened for increasing capacities of drives. In the
magnetic record media for the longitudinal magnetic recording
systems currently used worldwide, however, an attempt to realize a
high record density leads to refined record bits, which require a
high coercivity to such an extent that recording cannot be made
with the record bits. In view of this, a perpendicular magnetic
recording system is under study as a means of solving these
problems and improving the record densities.
[0004] The perpendicular magnetic recording system is a system in
which a magnetization-easy axis is oriented in the direction
vertical to a medium surface in the magnetic film of the
perpendicular magnetic record medium, and is suitable for high
record densities. In addition, as for the perpendicular magnetic
recording system, a two-layered record medium has been developed
having a magnetic record film layer where the record sensitivity is
improved and a soft magnetic film layer. A CoCrPt--SiO.sub.2 based
alloy is generally used in the magnetic record film layer.
[0005] On the other hand, it is proposed that a soft magnetic film
of a Fe--Co--B based alloy is used as a soft magnetic film of a
two-layered record medium. For example, as disclosed in Japanese
Patent Laid-Open Publication No. 346423/2004, there is proposed a
Fe--Co--B based alloy target material in which the diameter of the
maximum inscribed circle which can be drawn in a region with no
boride phase in a cross-microstructure is equal to 30 .mu.m or
less.
[0006] Magnetron sputtering method is generally used for the
preparation of the aforementioned soft magnetic film. This
magnetron sputtering method is a method in which a magnet is
disposed behind a target material to leak the magnetic flux onto a
surface of the target material for converging plasma in the leaked
magnetic flux region, enabling a high-speed coating. Since the
magnetron sputtering method has a feature of leaking the magnetic
flux on the sputtering surface of the target material, in the case
where magnetic permeability of the target material itself is high,
it is difficult to form, on the sputtering surface of the target
material, the leaked magnetic flux necessary and sufficient for the
magnetron sputtering method. In view of this, Japanese Patent
Laid-Open Publication No. 346423/2004 is proposed for a demand for
reducing the magnetic permeability of the target material itself as
much as possible.
[0007] On the other hand, the thickness of the target material can
be increased as the magnetic permeability of the target material is
lowered. That is, a larger number of thin films can be produced
from a single target material, resulting in an improved
productivity. However, in the foregoing conventional technique,
since the magnetic permeability is not sufficiently low, the
maximum thickness of the target material is about 5 mm. If the
thickness exceeds 5 mm, leaked magnetic flux is insufficiently
created on the surface of the target material, causing a problem
that a magnetron sputtering cannot be performed normally.
DISCLOSURE OF THE INVENTION
[0008] The inventors have now found that a target material having a
high density and a magnetic permeability lower than the
conventional one can be produced by mixing a first raw-material
powder having a certain Fe:Co weight ratio and a second
raw-material powder having another certain Fe:Co weight ratio so
that the resulting Fe:Co weight ratio becomes between 8:2 and 2:8,
followed by hot-pressing the powder mixture into which a certain
additional element of 3 to 15 atom % is added.
[0009] It is therefore an object of the present invention to
provide an Fe--Co based target material and a method for producing
the Fe--Co based target material capable of ensuring a high density
and lowering the magnetic permeability than conventional targets so
that the thickness of the target material can be increased to
improve productivity of thin-films.
[0010] The present invention provides a method for producing a
Fe--Co based target material, comprising the steps of:
[0011] preparing a first raw-material powder having an Fe:Co weight
ratio ranging from 8:2 to 7:3 and a second raw-material powder
having an Fe--Co weight ratio ranging from 2:8 to 0:10;
[0012] mixing the first raw-material powder and the second
raw-material powder together to obtain a powder mixture having an
Fe:Co weight ratio ranging from 8:2 to 2:8; and
[0013] applying a pressure of not less than 100 MPa to the powder
mixture at a temperature ranging from 1073 to 1473 K for
consolidation,
[0014] wherein at least one additional element selected from the
group consisting of Nb, Zr, Ta and Hf is added to either one or
both of the first and second raw-material powders in a total amount
of 3 to 15 atom % with respect to the total amount of the powder
mixture.
[0015] The present invention also provides an Fe--Co based target
material, which is obtainable by the above method, wherein the
Fe--Co based target material is made of an Fe--Co based alloy
comprising:
[0016] 85 to 97 atom % of Fe and Co, which have a Fe:Co weight
ratio ranging from 8:2 to 2:8; and
[0017] 3 to 15 atom % of at least one additional element selected
from the group consisting of Zr, Nb, Ta and Hf.
DETAILED DESCRIPTION OF THE INVENTION
Method for Producing Fe--Co Based Target Material
[0018] First of all, in the method for producing a Fe--Co based
target material according to the present invention, a first
raw-material powder having an Fe:Co weight ratio ranging from 8:2
to 7:3 and a second raw-material powder having a Fe--Co weight
ratio ranging from 2:8 to 0:10 are prepared. As far as the
composition of each of the first and second raw-material powders
falls within the above range, the magnetic characteristics
(magnetic permeability) are meaningfully reduced.
[0019] Then, the first raw-material powder and the second
raw-material powder are mixed together to obtain a powder mixture
having a Fe:Co weight ratio ranging from 8:2 to 2:8. As far as the
weight ratio falls within the above range, an increase in magnetic
characteristics (magnetic permeability) can be prevented.
[0020] In the production method of the present invention, at least
one additional element selected from the group consisting of Nb,
Zr, Ta and Hf is added to either one or both of the first and
second raw-material powders in a total amount of 3 to 15 atom %,
desirably, 5 to 10 atom %, with respect to the total amount of the
powder mixture. The additional element should be added to one or
both of the first and second raw-material powders in advance prior
to the mixing. The additional element of less than 3 atom % leads
to difficulty in amorphization even if the additional element is
added to the Fe--Co powder mixture. The additional element of more
than 15 atom % leads to a reduced saturation flux density.
According to a preferred aspect of the present invention, two
additional elements are preferably selected from the group
consisting of Nb, Zr, Ta and Hf.
[0021] According to a preferred aspect of the present invention, it
is preferred that, prior to the mixing step, the additional element
is added to the first raw-material powder in a total amount of not
less than 1 atom % with respect to the total amount of the first
raw-material powder, and/or, the additional element is added to the
second raw-material powder in a total amount of not less than 1
atom % with respect to the total amount of the second raw-material
powder. This makes it possible to fully achieve the effect of a
reduced magnetic permeability provided by the additional
element.
[0022] The powder mixture thus obtained is consolidated by applying
a pressure of not less than 100 MPa, preferably of 100 MPa to 500
MPa, at a temperature of 1073 to 1473 K to obtain a Fe--Co based
target material. The consolidating process usable in the method of
the present invention is not particularly limited and may be any
process, for example, hot consolidation such as HIP and hot
pressing, as far as the target material can be consolidated with a
high density. The method for producing powder is not limited to any
technique, and includes gas atomizing, water atomizing, and
casting-pulverizing. The reason why the consolidating temperature
is selected to the above range is that the density of the target
material does not reach 100% when the consolidating temperature is
less than 1073 K, and that when it exceeds 1473 K the diffusion
between particles is extremely promoted so that plenty of phases
having strong magnetic characteristics are formed. The reason why
the consolidating pressure is selected to the above range is that
when the consolidating pressure is less than 100 MPa, the density
does not reach 100%. While there is no problem as far as the
consolidating pressure is high, the upper limit of the
consolidating pressure is preferably at 500 MPa from the viewpoint
of cost and productivity.
Fe--Co Based Target Material
[0023] The Fe--Co based target material obtainable by the
production method of the present invention is made of an Fe--Co
based alloy comprising 85 to 97 atom % of Fe and Co, which have a
Fe:Co weight ratio ranging from 8:2 to 2:8; and 3 to 15 atom % of
at least one additional element selected from the group consisting
of Zr, Nb, Ta and Hf. The Fe--Co based target material thus
produced has a high density and a lower magnetic permeability than
those of conventional target materials. According to a preferred
aspect of the present invention, the Fe--Co based target material
has a magnetic permeability between 10 and 200. As a result, the
thickness of the target material can be increased to improve
productivity of thin-films. The magnetic permeability of the target
material of not more than 200 makes it possible to increase the
thickness of the target material, while the magnetic permeability
of not less than 10 results in satisfactory characteristics as a
magnetic material.
Sputtering Using Fe--Co Based Target Material
[0024] As described above, magnetron sputtering method is generally
used for forming soft magnetic films. This magnetron sputtering
method is a method in which a magnet is disposed behind a target
material to leak the magnetic flux onto a surface of the target
material for converging plasma in the leaked magnetic flux region,
enabling a high-speed coating. This magnetron sputtering device has
a feature that a magnet is disposed behind the target material to
trap .gamma. electrons in the vicinity of the target material by
the application of a magnetic field, aimed at solving the drawback
of bipolar DC glow discharge sputtering devices. Since the .gamma.
electron has such an orbit as to be entangled with the lines of
magnetic force, the plasma concentrates in the vicinity of the
target material to reduce damages to the substrate. In addition,
since the moving distance of the .gamma. electron becomes long, it
is possible to perform a high-speed sputtering at a low gas
pressure.
EXAMPLES
[0025] Examples of the present invention will be in detail
explained hereinafter.
[0026] As shown in Table 1, Fe--Co based alloys were produced by
gas-atomizing methods or casting method. The gas-atomizing methods
were carried out on condition that the type of gas was an argon
gas, the nozzle diameter was 6 mm and the gas pressure was 5 MPa.
On the other hand, the casting methods were carried out by melting
the alloys in a ceramic vessel (diameter: 200 mm; length: 30 mm)
and then pulverizing the alloys to powders. Powders thus produced
were classified into 500 .mu.m or less and each powder was stirred
for one hour by a V-type mixer.
[0027] Each powder thus produced was filled in an enclosing vessel
made of a SC steel having a diameter of 200 mm and a height of 100
mm and was encapsulated with vacuum evacuation at an ultimate
vacuum of 10.sup.-1 Pa or less, followed by an HIP (hot isostatic
pressing) at a temperature of 1173K under a pressure of 150 MPa for
a holding time of 5 hours. Next, the resultant consolidated bodies
were subjected to lathing and wire-cutting to provide final shapes
to obtain target materials having outer diameters of 180 mm and
thicknesses of 3 to 10 mm. Properties of the above target materials
are shown in Table 2. TABLE-US-00001 TABLE 1 Total Formulation
After Mixing Additional Raw-Material Powder A Raw-Material Powder B
Element Com- Additional Com- Additional Composition (at %) position
Element position Element Ratio Total of Ratio (at %) Ratio (at %)
No. Fe:Co Ratio Zr, Nb, Ta, Hf Fe Co Zr Nb Ta Hf Fe Co Zr Nb Ta Hf
1 8:2 7 74.2 25.8 4 3 -- -- -- -- Examples of 2 7:3 7 71 29 4 3 --
-- 0 100 1 1 Present Invention 3 6:4 7 76 24 4 3 -- -- 0 100 0 1 4
4:6 7 77 23 -- -- 3 3 0 100 1 0 5 3:7 10 73 27 4 3 -- -- 0 100 2 1
6 8:2 15 70 30 -- 4 5 5 11 89 0 0 1 7 7:3 14 71 29 6 8 -- -- 0 100
0 0 8 6:4 12 76 24 6 6 -- -- 11 89 0 0 9 4:6 15 77 23 -- -- 7 7 9
91 0 1 10 3:7 5 73 27 1 2 -- -- 13 87 1 1 11 7:3 14 71 29 6 8 -- --
0 100 0 0 12 6:4 14 76 24 6 6 -- -- 11 89 1 1 13 4:6 9 77 23 -- --
4 4 9 91 1 0 14 1:8 11 100 0 -- 4 5 5 16 84 1 1 1 Comparative 15
9:1 7 73 27 4 3 -- -- 0 100 0 0 Examples 16 3:7 16 70 30 8 8 -- --
0 100 0 0 17 3:7 16 70 30 -- -- 8 8 0 100 0 0 18 7:3 15 89 11 -- 4
5 5 11 89 1 0 19 7:3 10 76 24 -- 4 5 5 22 78 1 1 20 3:7 9 73 27 4 3
-- -- 0 100 1 1 21 7:3 14 69 31 6 8 -- -- 0 100 1 1 (Underlined
part is out of the range of the conditions of the present
invention)
[0028] TABLE-US-00002 TABLE 2 Con- solidating Consolidating
Magnetic Relative Temperature Pressure Per- Density No. (K) (MPa)
meability (%) 1 1173 150 100 100 Examples of 2 1173 200 90 100
Present 3 1223 180 85 100 Invention 4 1123 220 110 100 5 1223 220
120 100 6 1173 180 100 100 7 1173 200 90 100 8 1223 220 85 100 9
1123 200 110 100 10 1223 250 120 100 11 1073 200 90 100 12 1373 180
85 100 13 1123 200 110 100 14 1223 200 200 100 Comparative 15 1223
200 250 100 Examples 16 1223 180 5 100 17 1223 280 5 100 18 1223
200 250 100 19 1223 200 220 100 20 1523 200 250 100 21 1023 200 240
96 (Underlined part is out of the range of the conditions of the
present invention)
[0029] In order to evaluate the characteristics of the target
materials thus produced, the following measurements were carried
out.
(1) Magnetic Permeability Measurements
[0030] Preparation of ring specimens: outer diameter of 15 mm,
inner diameter of 10 mm, height of 5 mm
[0031] Apparatus: BH tracer
[0032] Applied magnetic field: 8 kA/m
[0033] Measurement item: mean magnetic permeability between zero
and 100 A/m(Oe)
(2) Density
[0034] The density measurement was made by the use of Archimedes'
principle to calculate a relative density (ratio of a measured
density to a calculated density).
[0035] As shown in Table 1, No. 1 to No. 13 are examples of the
present invention, and No. 14 to No. 21 are comparative examples.
In comparative example No. 14, the Fe:Co ratio as a whole after the
mixing step is 1:8, which indicates a low Fe content and a high Co
content, resulting in a high magnetic permeability as a magnetic
characteristic. In comparative example No. 15, the Fe:Co ratio as a
whole after the mixing step is 9:1, which indicates a high Fe
content and a low Co content, resulting in a high magnetic
permeability as the magnetic characteristic. In comparative example
No. 16, the content of Zr and Nb as the additional elements is
high, resulting in a low magnetic permeability. In comparative
example No. 17, the content of Ta and Hf as the additional elements
is high, resulting in a low magnetic permeability.
[0036] In comparative example No. 18, the first raw-material powder
has the high Fe ratio and the low Co ratio, resulting in a high
magnetic permeability. In comparative example No. 19, the second
raw-material powder has the low Fe ratio and the high Co ratio,
resulting in a high magnetic permeability. In comparative example
No. 20, phases with strong magnetic characteristics are formed by a
reaction due to the high consolidating temperature, resulting in a
high magnetic permeability. In comparative Example No. 21, the
first raw-material powder has the low Fe ratio and the high Co
ratio, resulting in a high magnetic permeability, and the relative
density is inferior because of the low consolidating
temperature.
[0037] In contrast, it can be seen that all examples No. 1 to No.
13 of the present invention are superior in magnetic permeability
as a magnetic characteristic because examples No. 1 to No. 13
satisfy the conditions of the present invention.
[0038] As described above, a Fe:Co ratio is determined for each of
the first and second raw-material powders, and the total Fe:Co
ratio is controlled to fall within an optimum range for the powder
mixture to which a certain amount of an additional element is
added. This leads to a magnetic permeability as a magnetic
characteristic which is lower than the conventional one, making it
possible to increase the thickness of the target material and thus
to improve productivity. In consequence, significantly advantageous
effects are attained.
* * * * *