U.S. patent application number 16/468769 was filed with the patent office on 2021-06-10 for sputtering target, method for producing laminated film, laminated film and magnetic recording medium.
The applicant listed for this patent is JX Nippon Mining & Metals Corporation. Invention is credited to Yasuyuki Iwabuchi, Manami Masuda, Masayoshi Shimizu.
Application Number | 20210172050 16/468769 |
Document ID | / |
Family ID | 1000005431949 |
Filed Date | 2021-06-10 |
United States Patent
Application |
20210172050 |
Kind Code |
A1 |
Shimizu; Masayoshi ; et
al. |
June 10, 2021 |
SPUTTERING TARGET, METHOD FOR PRODUCING LAMINATED FILM, LAMINATED
FILM AND MAGNETIC RECORDING MEDIUM
Abstract
A sputtering target according to the present invention contains
Co and Pt as metal components, wherein a molar ratio of a content
of Pt to a content of Co is from 5/100 to 45/100, and wherein the
sputtering target contains Nb.sub.2O.sub.5 as a metal oxide
component.
Inventors: |
Shimizu; Masayoshi;
(Ibaraki, JP) ; Iwabuchi; Yasuyuki; (Ibaraki,
JP) ; Masuda; Manami; (Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JX Nippon Mining & Metals Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
1000005431949 |
Appl. No.: |
16/468769 |
Filed: |
August 16, 2018 |
PCT Filed: |
August 16, 2018 |
PCT NO: |
PCT/JP2018/030435 |
371 Date: |
June 12, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 14/165 20130101;
G11B 5/851 20130101; G11B 5/70621 20130101; C23C 14/083 20130101;
G11B 5/73919 20190501; C23C 14/3407 20130101; H01F 41/18 20130101;
G11B 5/7353 20190501; G11B 5/73921 20190501 |
International
Class: |
C23C 14/16 20060101
C23C014/16; C23C 14/08 20060101 C23C014/08; C23C 14/34 20060101
C23C014/34; G11B 5/851 20060101 G11B005/851; G11B 5/735 20060101
G11B005/735; G11B 5/706 20060101 G11B005/706; H01F 41/18 20060101
H01F041/18 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2017 |
JP |
2017-180829 |
Claims
1. A sputtering target containing Co and Pt as metal components,
wherein a molar ratio of a content of Pt to a content of Co is from
5/100 to 45/100, and wherein the sputtering target contains
Nb.sub.2O.sub.5 as a metal oxide component.
2. The sputtering target according to claim 1, wherein the
sputtering target has a content of Nb.sub.2O.sub.5 of from 0.5 mol
% to 5 mol %.
3. The sputtering target according to claim 1, wherein the
sputtering target further contains TiO.sub.2 as a metal oxide
component.
4. The sputtering target according to claim 3, wherein the
sputtering target has a content of TiO.sub.2 of from 0.5 mol % to
15 mol %.
5. The sputtering target according to claim 3, wherein the
sputtering target has a phase including all of Ti, Nb and O.
6. The sputtering target according to claim 1, wherein the
sputtering target further contains at least one metal oxide of
SiO.sub.2 and B.sub.2O.sub.3 as a metal oxide component, and
wherein the sputtering target has a total content of metal oxides
including Nb.sub.2O.sub.5 of from 20 vol % to 40 vol %.
7. The sputtering target according to claim 1, wherein the
sputtering target has a molar ratio of a content of Pt to a content
of Co of from 15/100 to 35/100.
8. The sputtering target according to claim 1, wherein the
sputtering target contains Pt in an amount of from 2 mol % to 25
mol %.
9. The sputtering target according to claim 1, wherein the
sputtering target further contains Cr and/or Ru as a metal
component(s) in an amount of from 0.5 mol % to 20 mol %.
10. A method for producing a laminated film, the method comprising:
forming, by sputtering using the sputtering target according to
claim 1, a magnetic layer on a base layer containing Ru or on an
intermediate layer formed on the base layer by sputtering using a
sputtering target containing Co and at least one metal selected
from the group consisting of Cr and Ru as a metal component.
11. A laminated film, comprising: a base layer containing Ru; and a
magnetic layer directly formed on the base layer or indirectly
formed on the base layer via an intermediate layer containing Co
and at least one metal selected from the group consisting of Cr and
Ru as a metal component, the magnetic layer containing Co and Pt as
metal components and having a molar ratio of a content of Pt to a
content of Co of from 5/100 to 45/100; wherein the magnetic layer
contains Nb.sub.2O.sub.5 as a metal oxide component.
12. The laminated film according to claim 11, wherein the magnetic
layer further contains TiO.sub.2 as a metal oxide component.
13. A magnetic recording medium comprising the laminated film
according to claim 11.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sputtering target which
contains Co and Pt as metal components and is suitable for use in
forming a magnetic layer onto an intermediate layer or the like of
a perpendicular magnetic recording medium, for example; to a method
for producing a laminated film; and to a magnetic recording medium.
More particularly, the present invention proposes a technique
capable of contributing to production of a hard disk drive having
high density.
BACKGROUND ART
[0002] In a hard disk drive, a perpendicular magnetic recording
system for recording magnetism in a direction perpendicular to a
recording surface has been put to practical use. This method is
widely adopted because it enables high-density recording as
compared with an in-plane magnetic recording method.
[0003] The magnetic recording medium in the perpendicular magnetic
recording method generally has a structure in which a base layer
such as an adhesion layer, a soft magnetic layer, a seed layer and
a Ru layer, an intermediate layer, a magnetic layer, and a
protective layer, and the like are sequentially laminated on a
substrate such as aluminum or glass. Among them, in a lower part of
the magnetic layer is a granular film in which SiO.sub.2 or other
metal oxide is dispersed in a Co--Pt based alloy containing Co as a
main component, and the granular layer has high saturation
magnetization Ms and magnetic anisotropy Ku. Further, the
intermediate layer laminated on a lower side of the magnetic layer
includes a structure having a Co--Cr--Ru based alloy or the like
dispersing the similar metal oxide therein. The intermediate layer
may contain a relatively large amount of Ru, Cr or the like in
order to render the intermediate layer nonmagnetic.
[0004] In such a magnetic layer and an intermediate layer, the
above metal oxide that will be a nonmagnetic material is
precipitated at grain boundaries of magnetic particles such as a Co
alloy or the like oriented in the vertical direction to reduce
magnetic interaction, thereby improving noise characteristics and
achieving high recording density.
[0005] In general, each layer such as the magnetic layer and the
intermediate layer is formed by sputtering a material onto a
substrate using a sputtering target having a predetermined
composition or structure to form a film. Conventionally, such a
type of technology is disclosed in Patent Document 1 and the
like.
CITATION LIST
Patent Literature
[0006] Patent Document 1: Japanese Patent No. 5960287 B
SUMMARY OF INVENTION
Technical Problem
[0007] To realize high density of the hard disk drive, there are
needs for an increase in the magnetic anisotropy Ku for ensuring
thermal stability and high magnetic separation of the magnetic
particles for high resolution.
[0008] However, the magnetic layer having high saturation
magnetization Ms as described above has a strong exchange coupling
between the magnetic particles, so that the magnetic layer has poor
magnetic separation of the magnetic particles. Here, if a large
amount of a metal oxide is added in order to improve the magnetic
separation, the metal oxide will enter the magnetic particles to
deteriorate crystallinity of the magnetic particles, whereby the
saturation magnetization Ms and the magnetic anisotropy Ku are
decreased accordingly.
[0009] An object of this invention is to solve such problems of the
prior art. An object of this invention is to provide a sputtering
target, a method for producing a laminated film, a laminated film
and a magnetic recording medium, which can improve magnetic
separation between the magnetic particles, without significantly
lowering magnetic anisotropy of a magnetic layer in a magnetic
recording medium.
Solution to Problem
[0010] As a result of intensive studies, the inventors have found
that when Nb.sub.2O.sub.5 is used as a metal oxide for a
nonmagnetic material to be dispersed in a Co alloy which is a
magnetic material for a magnetic layer and an intermediate layer,
in addition to or in place of SiO.sub.2 conventionally used, the
magnetic separation between the magnetic particles can be
significantly improved even if the content of the metal oxide is
not increased so much. Further, the present inventors have found
that this can allow high saturation magnetization Ms and high
magnetic anisotropy Ku of the magnetic layer mainly based on Co--Pt
to be maintained. Furthermore, the present inventors have found
that containing both Nb.sub.2O.sub.5 and TiO.sub.2 provides further
higher Ms and Ku while maintaining magnetic separation.
[0011] It is believed that this is because Nb.sub.2O.sub.5 has
reasonable wettability to Co and can form a stable oxide even if a
part of oxygen is lacked so that a grain boundary having a uniform
width can be formed around the magnetic grains without penetrating
the oxide in the magnetic grains, although the present invention is
limited to such a theory.
[0012] Based on such findings, a sputtering target according to the
present invention contains Co and Pt as metal components, wherein a
molar ratio of a content of Pt to a content of Co is from 5/100 to
45/100, and wherein the sputtering target contains Nb.sub.2O.sub.5
as a metal oxide component.
[0013] Preferably, the sputtering target according to the present
invention further contains TiO.sub.2 as a metal oxide
component.
[0014] It is preferable that the sputtering target according to the
present invention has a content of Nb.sub.2O.sub.5 of from 0.5 mol
% to 5 mol %. When TiO.sub.2 is contained, the content of TiO.sub.2
is preferably from 0.5 mol % to 15 mol %.
[0015] Further, it is preferable that the sputtering target
according to the present invention has a phase including all of Ti,
Nb and O.
[0016] It is preferable that the sputtering target according to the
present invention further contains at least one metal oxide of
SiO.sub.2 and B.sub.2O.sub.3 as a metal oxide component, and
wherein the sputtering target has a total content of metal oxides
including Nb.sub.2O.sub.5 of from 20 vol % to 40 vol %.
[0017] Preferably, the sputtering target according to the present
invention has a molar ratio of a content of Pt to a content of Co
of from 15/100 to 35/100.
[0018] Preferably, the sputtering target according to the present
invention contains Pt in an amount of from 2 mol % to 25 mol %.
[0019] In addition, the sputtering target according to the present
invention may further contain Cr and/or Ru as a metal component(s)
in an amount of from 0.5 mol % to 20 mol %.
[0020] A method for producing a laminated film according to the
present invention comprises forming, by sputtering using any one of
the sputtering targets described above, a magnetic layer on a base
layer containing Ru or on an intermediate layer formed on the base
layer by sputtering using a sputtering target containing Co and at
least one metal selected from the group consisting of Cr and Ru as
a metal component.
[0021] A laminated film according to the present invention
comprises: a base layer containing Ru; and a magnetic layer
directly formed on the base layer or indirectly formed on the base
layer via an intermediate layer containing Co and at least one
metal selected from the group consisting of Cr and Ru as a metal
component, the magnetic layer containing Co and Pt as metal
components and having a molar ratio of a content of Pt to a content
of Co of from 5/100 to 45/100; wherein the magnetic layer contains
Nb.sub.2O.sub.5, preferably TiO.sub.2 in addition to
Nb.sub.2O.sub.5, as a metal oxide component(s).
[0022] A magnetic recording medium according to the present
invention comprises the laminated film as described above.
Advantageous Effects of Invention
[0023] According to the present invention, at least
Nb.sub.2O.sub.5, preferably Nb.sub.2O.sub.5 together with TiO.sub.2
is/are contained as a metal oxide component(s), so that it is
possible to achieve both good magnetic separation between magnetic
particles and high magnetic anisotropy Ku.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a schematic view showing a layer structure of a
laminated film produced in Examples.
[0025] FIG. 2 is a graph showing a change of saturation
magnetization Ms relative to a ratio Pt/Co in Examples.
[0026] FIG. 3 is a graph showing a change of magnetic anisotropy Ku
relative to a ratio Pt/Co in Examples.
[0027] FIG. 4 is a graph showing a change of a slope a of a
magnetization curve relative to a ratio Pt/Co in Examples.
[0028] FIG. 5 is SEM/EDS mapping images of targets in Examples.
[0029] FIG. 6 is a graph showing a result of identification of a
crystal structure using XRD of a target in Examples.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Embodiments of the present invention will be described in
detail below.
[0031] In an embodiment, a sputtering target according to the
present invention contains Co and Pt as metal components, and has a
molar ratio of a content of Pt to a content of Co of from 5/100 to
45/100, and contains Nb.sub.2O.sub.5 or Nb.sub.2O.sub.5 and
SiO.sub.2 as a metal oxide component(s).
[0032] More particularly, the sputtering target has a structure in
which metal oxides containing Nb.sub.2O.sub.5 are dispersed in an
alloy made of Co and Pt. When both TiO.sub.2 and Nb.sub.2O.sub.5
are contained, the sputtering target has a structure in which a
solid solution of TiO.sub.2 and Nb.sub.2O.sub.5 is dispersed as
metal oxides.
[0033] The sputtering target is preferably used for forming a
magnetic layer, in particular located onto an intermediate layer in
a perpendicular magnetic recording type magnetic recording medium.
In this case, in the magnetic layer formed by sputtering using the
sputtering target, the above metal components form magnetic grains
and the metal oxides containing Nb.sub.2O.sub.5 form nonmagnetic
materials which are uniformly distributed around the magnetic
grains oriented in the vertical direction, so that the magnetic
interaction between the magnetic grains is effectively reduced.
(Composition)
[0034] The metal component of the sputtering target is mainly
composed of Co, and, in addition, contains Pt. In particular, the
metal component is a Co alloy containing Pt.
[0035] The content of Pt is preferably from 2 mol % to 25 mol %. If
the total content of Pt is too high, magnetic anisotropy may be
decreased or crystallinity of the magnetic grains may be decreased.
On the other hand, if the ratio of the total content of Pt to Co is
too low, the magnetic anisotropy may be insufficient.
[0036] Pt is contained in an amount such that a molar ratio to a
content of Co is from 5/100 to 45/100, because if the molar ratio
of the Pt content to the Co content is less than 5/100 or more than
45/100, the magnetic anisotropy is lowered. From the viewpoint, the
molar ratio of the Pt content to the Co content is more preferably
from 15/100 to 35/100. In addition, if the content of Co is too
high, the magnetic anisotropy may be lowered. On the other hand, if
the content of Co is too low, the saturation magnetization and the
magnetic anisotropy may be decreased.
[0037] The sputtering target according to the embodiment of the
present invention may further contain Cr and/or Ru in an amount of
from 0.5 mol % to 20 mol % as a metal component(s). The containing
of such a metal(s) provides an advantage that the saturation
magnetization and the magnetic anisotropy can be adjusted while
maintaining the crystallinity of the magnetic grains. In addition,
many of these metals are usually contained as metal components, but
some of them may be included as metal oxides by being oxidized by
sintering in the production, which will be described below.
[0038] The sputtering target according to the present invention
contains at least Nb.sub.2O.sub.5 as a metal oxide component.
Nb.sub.2O.sub.5 has better wettability to Co as compared with
SiO.sub.2 or the like which is the main metal oxide in the
conventional sputtering target, and forms a stable oxide even if a
part of oxide is lacked. Therefore, by containing Nb.sub.2O.sub.5,
the separation of magnetic grains can be improved while maintaining
the magnetic anisotropy. Further, by containing both
Nb.sub.2O.sub.5 and TiO.sub.2, higher Ms and Ku can be obtained
while maintaining the magnetic separation.
[0039] The content of Nb.sub.2O.sub.5 is preferably from 0.5 mol %
to 5 mol %. If the content of Nb.sub.2O.sub.5 is lower, there is a
possibility that the above effect cannot be sufficiently obtained.
On the other hand, if the content of Nb.sub.2O.sub.5 is higher, the
magnetic anisotropy may be decreased. Therefore, it is even more
preferable that the content of Nb.sub.2O.sub.5 is from 0.5 mol % to
3 mol %.
[0040] When TiO.sub.2 is contained, the content of TiO.sub.2 is
preferably from 0.5 mol % to 15 mol %. If the content of TiO.sub.2
is lower, there is a possibility that the above effect cannot be
sufficiently obtained. On the other hand, if the content of
TiO.sub.2 is higher, an oxide volume may be increased and the
magnetic anisotropy may be decreased.
[0041] Further, the sputtering target more preferably has a phase
containing all of Ti, Nb and O. Examples of such a phase includes a
solid solution phase in which Nb is mixed with TiO.sub.2, or a
solid solution phase in which Ti is mixed with Nb.sub.2O.sub.5, and
a complex oxide phase such as TiNb.sub.2O.sub.7 and
TiNb.sub.6O.sub.17. In this case, a part of oxygen may be lacked.
The phases in which Ti, Nb and O are mixed can be confirmed by
intensity signals of Nb, Ti and O from the same position by element
mapping using SEM/EDS, for example. Further, the solid solution
phase and the complex oxide phase can be confirmed by XRD
evaluation using X rays.
[0042] Further, the sputtering target according to the embodiment
of the present invention may contain metal oxides such as SiO.sub.2
and B.sub.2O.sub.3 in addition to Nb.sub.2O.sub.5 and TiO.sub.2 as
metal oxide components.
[0043] When containing the above metal oxides other than
Nb.sub.2O.sub.5, the total content of all of the metal oxides
including Nb.sub.2O.sub.5 is preferably from 20 vol % to 40 vol %.
If the total content of the metal oxides is less than 20 vol %, the
separation of the magnetic grains may become insufficient. On the
other hand, if it is more than 40 vol %, the saturation
magnetization may be decreased. For these reasons, it is more
preferable that the total content of metal oxides is from 25 vol %
to 35 vol %.
(Method for Producing Sputtering Target)
[0044] The above sputtering target can be produced by a powder
sintering method, and specific examples thereof are as follows.
[0045] First, as metal powder, Co powder and Pt powder, and
optionally further powder of the other metals as described above,
are prepared. The metal powder may be powder of not only a single
element but also an alloy. The particle diameter of the metal power
is preferably in a range of from 1 .mu.m to 10 .mu.m, in terms of
enabling homogeneous mixing to prevent segregation and coarse
crystallization. When the particle size of the metal powder is more
than 10 .mu.m, oxide particles as described below may not be
uniformly dispersed, and when it is less than 1 .mu.m, the
sputtering target may deviate from the desired composition due to
the oxidation of the metal powder.
[0046] Further, as the oxide powder, at least Nb.sub.2O.sub.5
powder and optionally at least one powder selected from the group
consisting of TiO.sub.2 powder, SiO.sub.2 powder and B.sub.2O.sub.3
powder are prepared. The oxide powder has a particle diameter in a
range of from 1 .mu.m to 30 .mu.m. This can lead to more uniform
dispersion of the oxide particles in the metal phase when the oxide
powder is mixed with the metal powder, and fired under pressure. If
the particle diameter of the oxide powder is more than 30 .mu.m,
coarse oxide particles may be formed after firing under pressure.
On the other hand, if it is less than 1 .mu.m, agglomeration of the
oxide powders may occur.
[0047] The above metal powder and oxide powder are weighed so as to
provide a desired composition, and mixed and pulverized using a
known way such as a ball mill. In this case, it is desirable to
fill the inside of a container used for the mixing/pulverizing with
an inert gas to suppress the oxidation of the raw material powder
as much as possible. This can provide mixed powder in which
predetermined metal powder and oxide powder are uniformly
mixed.
[0048] The mixed powder thus obtained is then sintered under
pressure in a vacuum atmosphere or an inert gas atmosphere, and
formed into a predetermined shape such as a disk shape. Herein,
various pressure sintering methods can be employed such as a hot
press sintering method, a hot hydrostatic sintering method, a
plasma discharge sintering method and the like. Among them, the hot
hydrostatic sintering method is effective in terms of improvement
of density of a sintered body.
[0049] A retention temperature during the sintering is in a
temperature range of from 700 to 1500.degree. C., and particularly
preferably from 800.degree. C. to 1400.degree. C. A time for
maintaining the temperature in this range is preferably 1 hour or
more.
[0050] A pressing pressure during the sintering is preferably from
10 MPa to 40 MPa, and more preferably from 25 MPa to 35 MPa.
[0051] This can allow the oxide particles to be more uniformly
dispersed in the metal phase.
[0052] The sintered body obtained by the pressure sintering can be
subjected to cutting into a desired shape using a lathe or the like
or other mechanical processing to produce a sputtering target.
(Laminated Film)
[0053] The laminated film includes, at least, a base layer; and a
magnetic layer formed on the base layer.
[0054] More particularly, the base layer contains Ru, and
generally, it is composed of Ru, or it is a layer mainly based on
Ru.
[0055] An intermediate layer can be provided between the base layer
and the magnetic layer. The intermediate layer contains, as metal
components, Co and at least one metal selected from the group
consisting of Cr and Ru, has a molar ratio of the content of at
least one metal selected from the group consisting of Cr and Ru to
the content of Co of 1/2 or more. Further, the intermediate layer
preferably contains at least one selected from the group consisting
of Nb.sub.2O.sub.5, TiO.sub.2, SiO.sub.2, B.sub.2O.sub.3, CoO,
Co.sub.3O.sub.4, Cr.sub.2O.sub.3, Ta.sub.2O.sub.5, ZnO and MnO as a
metal oxide component. Among them, Nb.sub.2O.sub.5 is preferably
contained.
[0056] Further, the content of Nb.sub.2O.sub.5 in the intermediate
layer may be from 5 mol % to 15 mol %, or when the intermediate
layer contains other metal oxides, the content of Nb.sub.2O.sub.5
may be from 2 mol % to 5 mol %. The intermediate layer may further
contain the above metal oxides other than Nb.sub.2O.sub.5 and may
have a total content of metal oxides including Nb.sub.2O.sub.5 of
30 vol % or more.
[0057] The Co content in the intermediate layer may be from 15 mol
% to 60 mol %, and the total content of Cr and Ru may be from 30
mol % to 60 mol %. In addition, the intermediate layer may further
contain Pt in an amount of from 2 mol % to 25 mol % as a metal
component.
[0058] Preferably, the magnetic layer contains Co and Pt as metal
components, has a molar ratio of a content of Pt to a content of Co
of from 5/100 to 45/100, and preferably from 15/100 to 35/100, and
contains Nb.sub.2O.sub.5 as a metal oxide component. The containing
of Nb.sub.2O.sub.5 in the magnetic layer can lead to improved
magnetic separation of the magnetic grains. Further, the containing
of both Nb.sub.2O.sub.5 and TiO.sub.2 can increase Ms and Ku while
maintaining magnetic separation.
[0059] The magnetic layer can be formed on the intermediate layer
by sputtering using the above sputtering target.
[0060] Therefore, as with the sputtering target as described above,
it is preferable that the magnetic layer has a content of
Nb.sub.2O.sub.5 of from 0.5 mol % to 5 mol %, and when TiO.sub.2 is
contained, it has a content of TiO.sub.2 of from 0.5 mol % to 15
mol %, and when the magnetic layer further contains at least one
metal oxide selected from the group consisting of SiO.sub.2 and
B.sub.2O.sub.3 as a metal oxide components, it has the total
content of metal oxides including Nb.sub.2O.sub.5 of from 20 vol %
to 40 mol %, and the magnetic layer contains Pt in an amount of
from 2 mol % to 25 mol %, and the magnetic layer further contains
Cr and/or Ru in an amount of from 0.5 mol % to 20 mol % as a metal
component(s).
(Method for Producing Laminated Film)
[0061] Each layer in the laminated film can be produced by forming
each film with a magnetron sputtering apparatus or the like using a
sputtering target having a composition and a structure
corresponding to each layer thereof.
[0062] Here, the intermediate layer in the laminated film is formed
on the base layer by sputtering using a sputtering target
containing Co and at least one metal selected from the group
consisting of Cr and Ru.
[0063] The magnetic layer in the laminated film can be formed on
the intermediate layer by sputtering using the sputtering target as
described above.
(Magnetic Recording Medium)
[0064] The magnetic recording medium is provided with the laminated
film including the base layer, the intermediate layer formed on the
base layer, and the magnetic layer formed on the intermediate layer
as described above. The magnetic recording medium is usually
produced by sequentially forming a soft magnetic layer, a base
layer, an intermediate layer, a magnetic layer, a protective layer,
and the like on a substrate made of aluminum, glass or the
like.
EXAMPLES
[0065] Next, the sputtering target according to present invention
was experimentally conducted and effects exerted by a magnetic
layer formed by the sputtering target were confirmed as described
below. However, the description herein is merely for the purpose of
illustration and is not intended to be limited thereto.
[0066] Using various sputtering targets, each laminated film having
the layer structure shown in FIG. 1 was produced.
[0067] Here, the magnetic layers shown as "Mag" in FIG. 1 were
formed from the sputtering targets having different compositions as
shown in Table 1. Saturation magnetization Ms, magnetic anisotropy
Ku, and a slope .alpha. of a magnetization curve for a coercive
force of each laminated film having each of the magnetic layers
were measured, respectively.
[0068] Here, the saturation magnetization Ms and the slope a of the
magnetization curve were measured with a vibrated sample type
magnetometer (VSM) available from TAMAGAWA CO., LTD., and the
magnetic anisotropy Ku was measured by a magnetic torque meter
(TRQ) available from TAMAGAWA CO., LTD. A volume fraction of the
oxide was determined by calculating a volume of the entire target
and a volume of the oxide based on the density and weight of the
raw material powder, and obtaining a ratio of them.
[0069] In Table 1, "x" in the "Effect" section means that there was
no reduction effect of .alpha., ".largecircle." means that there
was a reduction effect of .alpha., and ".circleincircle." means
that there was a remarkable reduction effect of .alpha.,
respectively.
TABLE-US-00001 TABLE 1 Co Pt Contained Contained Oxide Pt/Co Molar
Molar Volume Target Composition Ratio Ratio Ratio Fraction Ms Ku
.alpha. Effect Example 1 (Co--5Pt)--1.5Nb2O5--5TiO2--4SiO2 0.05
85.0 4.5 31.0 800 2 2.4 .largecircle. Example 2
(Co--10Pt)--1.5Nb2O5--5TiO2--4SiO2 0.11 80.6 9.0 31.0 780 5 2.3
.largecircle. Example 3 (Co--14Pt)--1.5Nb2O5--5TiO2--4SiO2 0.16
77.0 12.5 31.0 740 7.6 2.2 .largecircle. Example 4
(Co--16Pt)--1.5Nb2O5--5TiO2--4SiO2 0.19 75.2 14.3 31.0 732 8 1.9
.circleincircle. Example 5 (Co--18Pt)--1.5Nb2O5--5TiO2--4SiO2 0.22
73.4 16.1 31.0 722 8.3 2 .circleincircle. Example 6
(Co--21Pt)--1.5Nb2O5--5TiO2--4SiO2 0.27 70.7 18.8 31.0 704 8.5 2
.circleincircle. Example 7 (Co--23Pt)--1.5Nb2O5--5TiO2--4SiO2 0.30
68.9 20.6 31.0 693 8.8 1.8 .circleincircle. Example 8
(Co--25Pt)--1.5Nb2O5--5TiO2--4SiO2 0.33 67.1 22.4 31.0 673 9 1.9
.circleincircle. Example 9 (Co--26Pt)--1.5Nb2O5--5TiO2--4SiO2 0.35
66.2 23.3 31.0 662 8.7 1.8 .circleincircle. Example 10
(Co--28Pt)--1.5Nb2O5--5TiO2--4SiO2 0.39 64.4 25.1 31.0 643 8.3 1.9
.circleincircle. Example 11 (Co--30Pt)--1.5Nb2O5--5TiO2--4SiO2 0.43
62.7 26.9 31.0 618 8 1.9 .circleincircle. Example 12
(Co--31Pt)--1.5Nb2O5--5TiO2--4SiO2 0.45 61.8 27.7 31.0 605 7.4 2
.largecircle. Example 13 (Co--25Pt)--0.3Nb2O5--6.5TiO2--4.5SiO2
0.33 66.5 22.2 29.0 640 7.8 2.1 .largecircle. Example 14
(Co--25Pt)--0.5Nb2O5--5TiO2--6SiO2 0.33 66.4 22.1 30.9 681 9.2 2
.circleincircle. Example 15 (Co--25Pt)--1Nb2O5--6.5TiO2--4SiO2 0.33
66.4 22.1 31.1 680 9 1.9 .circleincircle. Example 16
(Co--25Pt)--3Nb2O5--3TiO2--2SiO2 0.33 69.0 23.0 29.9 670 8.5 1.7
.circleincircle. Example 17 (Co--25Pt)--5Nb2O5 0.33 71.3 23.8 29.6
580 7.2 1.7 .largecircle. Example 18 (Co--25Pt)--3Nb2O5--7.5TiO2
0.33 67.1 22.4 30.9 680 9.1 1.6 .circleincircle. Example 19
(Co--25Pt)--1.5Nb2O5--10TiO2 0.33 66.4 22.1 30.0 670 8.8 1.6
.circleincircle. Example 20 (Co--25Pt)--4.8Nb2O5--0.6TiO2 0.33 71.0
23.7 29.7 600 7.5 1.6 .circleincircle. Example 21
(Co--25Pt)--0.5Nb2O5--14TiO2 0.33 64.1 21.4 32.0 590 7.4 1.5
.circleincircle. Example 22 (Co--25Pt)--3Nb2O5--4SiO2 0.33 69.8
23.3 29.6 740 9.1 2.3 .largecircle. Example 23
(Co--25Pt)--1.5Nb2O5--7SiO2 0.33 68.6 22.9 29.6 750 9.3 2.4
.largecircle. Example 24
(Co--21Pt--4Cr--4Ru)--1.5Nb2O5--5TiO2--4SiO2 0.30 63.5 18.8 31.0
580 5.5 1.1 .circleincircle. Example 25
(Co--21Pt--4Cr)--1.5Nb2O5--5TiO2--4SiO2 0.28 67.1 18.8 31.0 630 6.5
1.3 .circleincircle. Example 26
(Co--21Pt--4Ru)--1.5Nb2O5--5TiO2--4SiO2 0.28 67.1 18.8 31.0 640 6
1.2 .circleincircle. Comp. 1 (Co--5Pt)--7TiO2--5.5SiO2 0.05 83.1
4.4 31.2 795 1.5 3 X Comp. 2 (Co--10Pt)--7TiO2--5.5SiO2 0.11 78.8
8.8 31.2 770 3.7 2.9 X Comp. 3 (Co--14Pt)--7TiO2--5.5SiO2 0.16 75.3
12.3 31.2 730 6.8 2.7 X Comp. 4 (Co--16Pt)--7TiO2--5.5SiO2 0.19
73.5 14.0 31.2 720 6.9 2.6 X Comp. 5 (Co--18Pt)--7TiO2--5.5SiO2
0.22 71.8 15.8 31.2 716 7.1 2.5 X Comp. 6
(Co--21Pt)--7TiO2--5.5SiO2 0.27 69.1 18.4 31.2 700 7.3 2.4 X Comp.
7 (Co--23Pt)--7TiO2--5.5SiO2 0.30 67.4 20.1 31.2 685 7.4 2.3 X
Comp. 8 (Co--25Pt)--7TiO2--5.5SiO2 0.33 65.6 21.9 31.2 660 7.45 2.5
X Comp. 9 (Co--26Pt)--7TiO2--5.5SiO2 0.35 64.8 22.8 31.2 651 7.35
2.4 X Comp. 10 (Co--28Pt)--7TiO2--5.5SiO2 0.39 63.0 24.5 31.2 636
7.2 2.3 X Comp. 11 (Co--30Pt)--7TiO2--5.5SiO2 0.43 61.3 26.3 31.2
605 6.9 2.4 X Comp. 12 (Co--31Pt)--7TiO2--5.5SiO2 0.45 60.4 27.1
31.2 590 6.7 2.3 X Comp. 13 (Co--21Pt--4Cr--4Ru)--7TiO2--5.5SiO2
0.30 62.1 18.4 31.2 576 5 2 X Comp. 14
(Co--21Pt--4Cr)--7TiO2--5.5SiO2 0.28 65.6 18.4 31.2 628 6.1 2.2 X
Comp. 15 (Co--21Pt--4Ru)--7TiO2--5.5SiO2 0.28 65.6 18.4 31.2 635
5.7 2.1 X
[0070] From the results shown in Table 1, it is found that in
Inventive Examples 1 to 26 containing Nb.sub.2O.sub.5, the slope
.alpha. of the magnetization curve is effectively reduced while
maintaining the relatively high saturation magnetization Ms and
magnetic anisotropy Ku. However, in Comparative Examples 1 to 15
which did not contain Nb.sub.2O.sub.5, the slope .alpha. of the
magnetization curve was not reduced.
[0071] Further, each of Inventive Examples 1 to 12 and Comparative
Examples 1 to 12 in Table 1 was confirmed for each change of the
saturation magnetization Ms, the magnetic anisotropy Ku and the
slope a of the magnetization curve relative to the ratio Pt/Co. The
results are shown in graphs in FIGS. 2 to 4, respectively.
[0072] For reference, two graphs (which correspond to Invention
Examples 19 and 18, respectively) of SEM/EDS mapping images of the
targets and the identification results of the crystal structures of
the targets using XRD are shown in FIGS. 5 and 6.
[0073] In view of the foregoing, it was suggested that according to
the present invention, the magnetic separation between the magnetic
particles can be improved without greatly decreasing the magnetic
anisotropy in the magnetic layer of the magnetic recording
medium.
* * * * *