U.S. patent number RE36,517 [Application Number 09/172,876] was granted by the patent office on 2000-01-18 for thin film magnet, cylindrical ferromagnetic thin film and production method thereof.
This patent grant is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Takeshi Araki, Hideo Ikeda, Masashi Okabe, Yoshihiro Tani.
United States Patent |
RE36,517 |
Araki , et al. |
January 18, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Thin film magnet, cylindrical ferromagnetic thin film and
production method thereof
Abstract
A thin film magnet and a cylindrical ferromagnetic thin film
having a high maximum energy product (greater than 120 kJ/m.sup.3)
and thus suitable for use in miniature high performance devices are
provided. The thin film magnet is produced by means of physical
vapor deposition. The thin film magnet is an (Nd.sub.1-x
R.sub.x).sub.y M.sub.1-y-z B.sub.z alloy having a ferromagnetic
compound of the Nd.sub.2 Fe.sub.14 B type as its main phase,
wherein R is Tb, Ho, and Dy and M is Fe metal or an Fe-based alloy
including at least one of Co and Ni,
0.04.ltoreq.x.ltoreq.0.10,0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15. A perpendicular magnetization film
having such a composition is deposited on the side wall of a
substrate in the columnar (or cylindrical) form thereby obtaining a
cylindrical ferromagnetic thin film having radial anisotropy.
Inventors: |
Araki; Takeshi (Amagasaki,
JP), Tani; Yoshihiro (Amagasaki, JP),
Ikeda; Hideo (Amagasaki, JP), Okabe; Masashi
(Amagasaki, JP) |
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
16685921 |
Appl.
No.: |
09/172,876 |
Filed: |
October 15, 1998 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
525153 |
Sep 8, 1995 |
05676998 |
Oct 14, 1997 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Sep 9, 1994 [JP] |
|
|
6-216270 |
|
Current U.S.
Class: |
427/132; 427/128;
427/129; 427/131; 427/250; 427/294; 427/314; 427/404; 427/419.7;
428/704; 428/836.3 |
Current CPC
Class: |
C23C
14/06 (20130101); C23C 14/067 (20130101); C23C
14/28 (20130101); C23C 14/3464 (20130101); H01F
1/057 (20130101); H01F 10/126 (20130101); H01F
41/0273 (20130101); H01F 41/20 (20130101); Y10T
428/115 (20150115) |
Current International
Class: |
C23C
14/28 (20060101); C23C 14/06 (20060101); C23C
14/34 (20060101); H01F 41/02 (20060101); H01F
41/20 (20060101); H01F 1/057 (20060101); H01F
1/032 (20060101); H01F 10/12 (20060101); H01F
41/14 (20060101); B05D 005/12 () |
Field of
Search: |
;427/132,128,129,131,250,255.2,294,314,404,419.7,585
;428/694R,694T,694TS,704 |
Foreign Patent Documents
Other References
Cadieu et al, "High.sub.i H.sub.c Perpendicular Anisotrophy Nd-Fe-B
Sputtered Films", IEEE Transactions On Magnetics, vol. Mag-22, No.
5, Sep. 1986, pp. 752-754. .
Gu et al, "Crystallization Behavior and Magnetic Properties of
Amorphous Nd-Fe-B Thin Films", Phys. Stat. Sol. (a) 120, 1990, pp.
159-167 (no month avail.)..
|
Primary Examiner: Pianalto; Bernard
Attorney, Agent or Firm: Leydig, Vioit & Mayer, Ltd.
Claims
What is claimed is:
1. An article comprising a structure having a coating thereon
comprising a thin film magnet produced by means of physical vapor
deposition, said thin film magnet comprising an (Nd.sub.1-x
R.sub.x).sub.y M.sub.1-y-z B.sub.z alloy having a ferromagnetic
compound .[.comprising.]. .Iadd.with an .Iaddend.Nd.sub.2 Fe.sub.14
B .Iadd.structure type .Iaddend.as its main phase, wherein R is at
least one element selected from the group consisting of Tb, Ho, and
Dy and M is Fe metal or an Fe-based alloy consisting of at least
one element selected from the group consisting of Co and Ni,
0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15.
2. A method for producing an article comprising a thin film magnet
by forming a thin film magnet on a substrate placed in a vacuum
chamber, said thin film magnet comprising an (Nd.sub.1-x
R.sub.x).sub.y M.sub.1-y-z B.sub.z alloy having a ferromagnetic
compound .[.comprising.]. .Iadd.with an .Iaddend.Nd.sub.2 Fe.sub.14
B .Iadd.structure type .Iaddend.as its main phase, wherein R is at
least one element selected from the group consisting of Tb, Ho, and
Dy and M is Fe metal or an Fe-based alloy including at least one
element selected from the group consisting of Co and Ni,
0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15.
3. A method according to claim 2, wherein said substrate is heated
to a temperature in the range of from about 530.degree. to about
570.degree. C. during said formation step.
4. A method according to claim 2, wherein the deposition rate of
said magnetic thin film during said formation step is in the range
of from about 0.1 to about 4 .mu.m/hr.
5. A method according to claim 2, wherein said formation step is
carried out at a gas pressure in the range of from about 0.05 to
about 4 Pa.
6. An article comprising: a cylindrical or columnar substrate, and
a perpendicular magnetization film deposited on the side wall of
said substrate, said ferromagnetic thin film having radial
anisotropic magnetic properties.
7. An article according to claim 6, wherein said perpendicular
magnetization film is a thin film magnet comprising an (Nd.sub.1-x
R.sub.x).sub.y M.sub.1-y-z B alloy having a ferromagnetic compound
.[.comprising.]. .Iadd.with an .Iaddend.Nd.sub.2 Fe.sub.14 B
.Iadd.structure type .Iaddend.as its main phase, wherein R is at
least one element selected from the group consisting of Tb, Ho, and
Dy and M is Fe metal or an Fe-based alloy including at least one
element selected from the group consisting of Co and Ni,
0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15.
8. An article according to claim 6, wherein a buffer layer is
formed between said substrate and said perpendicular magnetization
film.
9. A method for producing a ferromagnetic thin film in cylindrical
form on a substrate by means of physical vapor deposition, said
method including the steps of heating a cylindrical or columnar
substrate, and depositing a perpendicular magnetization film on the
side wall of said substrate.
10. A method for producing a ferromagnetic thin film in cylindrical
form according to claim 9, wherein said perpendicular magnetization
film is a thin film magnet comprising an (Nd.sub.1-x R.sub.x)hd
yM.sub.1-y-z B.sub.z alloy having a ferromagnetic compound
.[.comprising.]. .Iadd.with an .Iaddend.Nd.sub.2 Fe.sub.14 B
.Iadd.structure type .Iaddend.as its main phase, wherein R is at
least one element selected from the group consisting of Tb, Ho, and
Dy and M is Fe metal or an Fe-based alloy including at least one
element selected from the group consisting of Co and Ni,
0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15.
11. A method for producing a ferromagnetic thin film in cylindrical
form according to claim 9, further including the step of forming a
buffer layer between said substrate and said perpendicular
magnetization film.
12. A method for producing a ferromagnetic thin film in cylindrical
form according to claim 9, wherein said substrate is heated to a
temperature in the range of from about 530.degree. to about
570.degree. C. during said heating step.
13. A method for producing a ferromagnetic thin film in cylindrical
form according to claim 9, wherein the deposition rate of said
magnetic thin film during said depositing step is in the range of
from about 0.1 to about 4 .mu.m/hr.
14. A method for producing a ferromagnetic thin film in cylindrical
form according to claim 9, wherein said depositing step is carried
out at a gas pressure in the range of from about 0.05 to about 4
Pa.
15. A method for producing a ferromagnetic thin film in cylindrical
form according to claim 9 comprising producing a ferromagnetic thin
film having radial anisotropic magnetic properties.
Description
The present invention relates to a thin film magnet a ferromagnetic
thin film in the form of a cylinder, and a production method
thereof. More particularly, the present invention relates to a thin
film magnet and a ferromagnetic thin film in the form of a cylinder
for use in small-sized or miniature devices such as miniature
electric motors, microwave oscillators, and micro-machines or
magnetic recording devices. The invention also relates to a
production method thereof.
BACKGROUND OF THE INVENTION
In recent years, significant advancements in performance as well as
in size and weight reductions have been made in various devices
such as video movie cameras, cassette tape recorders, communication
equipment etc. These devices need a small-sized magnet, which is
usually produced by machining a block of bonded or sintered magnet
material.
To improve the performance of such devices, it is desirable to
employ a magnet having a high maximum energy product. On the other
hand, in small-sized magnet applications, it is also required that
the magnet be easily machinable into a desired shape. Although
sintered magnets have a large maximum energy product ranging up to
370 kJ/m.sup.3, they are very brittle and thus difficult to machine
into a small size. Therefore, sintered magnets are unsuitable for
use as small-sized magnets. However, bonded magnets have the
advantage that they can be easily formed into a small size by
machining, and thus most common millimeter-sized magnets are now of
this type. However, this type of magnet has the disadvantage that
the maximum energy product is as low as 40 to 120 kJ/m.sup.3 for
mass-produced magnets and 170 kJ/m.sup.3 for Labaratory-produced
magnets.
Cylindrical magnets having radial anisotropy for use in miniature
motors, rotation sensors, or the like are produced by means of the
in-magnetic-field formation technique or the extrusion technique.
In the case of the in-magnetic-field formation technique, the inner
diameter of the cylindrical magnet must be above a minimum limit so
as to produce a magnetic field in a radial direction. At the
present time, the practical minimum outer diameter of a magnet of
this type is about 1 cm. When extrusion is employed, a mold having
a minimize size is needed to ensure that the mold can withstand
process pressures. Again, the current lower limit of the outer
diameter of the magnet is about 1 cm. These magnets are further
machined so as to obtain a good circular form with the dimensional
accuracy required for particular applications. However, the
above-described methods are unsuitable for producing cylindrical
magnets having radial anisotropy and a size of about a millimeter
or less.
In applications for micro-machines with a body size less than 1
cm.sup.3 to be used in examination and repair robots for industrial
and medical uses, magnets having a very small size such as a few
mm.sup.3 or less are required. However, such small-sized magnets
cannot be produced by means of practical machining techniques.
One known technique for producing such magnets is physical vapor
deposition such as by sputtering. This technique allows production
of small-sized magnets with submicron accuracy. This technique
allows control of various magnet characteristics, such as internal
stress, crystallinity, and crystal orientation, by adjusting film
deposition conditions. Utilizing various advantages of this
technique, rare earth alloy-based thin film magnets have recently
been developed. For example, Japanese Patent Laid-Open No. 4-99010
(1992) discloses a technique for producing a thin film magnet
having a maximum energy product as large as 80 to 111 kJ/m.sup.3 by
properly selecting the composition of Nd--(Fe, Co, Al)--B within a
certain range and also by properly selecting substrate temperature
and deposition rate.
To achieve a further size reduction while maintaining device
performance, it is necessary to use a magnet having a higher
maximum energy product than those of the bonded magnets which are
now widely used in small-sized devices. However, the maximum energy
product of the conventional thin film magnet is not greater than
that of the bonded magnet.
Furthermore, in the case of cylindrical magnets having radial
anisotropy for use in small-sized motors or small-sized rotation
sensors, the magnet must be formed in a circular shape having less
than about a 10 .mu.m deviation from an ideal circular shape and
also having high radial dimensional accuracy of a similar order. In
the conventional technique, as described above, a difficult
machining process is required to achieve such high dimensional
accuracy. The conventional technique has a further problem in that
it is difficult to produce a cylindrical magnet having radial
anisotropy with a size less than about a millimeter.
SUMMARY OF THE INVENTION
It is a general object of the present invention to solve the
problems described above. More specifically, it is an object of the
present invention to provide a thin film magnet and a production
method thereof; the thin film magnet having a maximum energy
product in the range of from 120 kJ/m.sup.3 to 220 kJ/m.sup.3,
wherein the above-described lower limit is greater than the maximum
energy product achieved in mass-produced bonded magnets.
It is another object of the present invention to provide a
cylindrical ferromagnetic element having radial anisotropy wherein
the element is formed in a circular shape having small deviations
only on the order of 1 .mu.m from an ideal circular shape and also
having high radial dimensional accuracy of a similar order.
It is a further object of the present invention to provide a
cylindrical ferromagnetic thin film having radial anisotropy whose
size is on the order of a millimeter or less.
According to the present invention there is provided a thin film
magnet produced by means of physical vapor deposition, the thin
film magnet comprising an (Nd.sub.1-x R.sub.x) .sub.y M.sub.1-y-z
B.sub.z alloy having a ferromagnetic .[.Compound.]. .Iadd.compound
.Iaddend.of the Nd.sub.2 Fe.sub.14 B .Iadd.structure .Iaddend.type
as its main phase, wherein R is at least one element selected from
the group consisting of Tb, Ho, and Dy and M is Fe metal or an
Fe-based alloy including at least one element selected from the
group consisting of Co and Ni, 0.04.ltoreq.x.ltoreq.0.10,
0.11.ltoreq.y.ltoreq.0.15, and 0.08.ltoreq.z.ltoreq.0.15. Such a
thin film magnet has a high residual magnetization or coercive
force and thus a high maximum energy product greater than 120
kJ/m.sup.3 which is greater than that of bonded magnets or
conventional thin film magnets.
According to the present invention, there is also provided a method
for producing a thin film magnet by forming a magnetic thin film by
physical vapor deposition on a substrate placed in a vacuum
chamber. The method is characterized in that the magnetic thin film
is deposited at a predetermined deposition rate and at a
predetermined gas pressure while heating the substrate at a
predetermined temperature so that the thin fire magnet comprises an
(Nd.sub.1-x R.sub.x).sub.y M.sub.1-y-z B.sub.z alloy having a
ferromagnetic compound of the Nd.sub.2 Fe.sub.14 B type as its main
phase, wherein R is at least one element selected from the group
consisting of Tb, Ho, and Dy and M is Fe metal or an Fe-based alloy
including at least one element selected from the group consisting
of Co and Ni, 0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15,
and 0.08.ltoreq.z.ltoreq.0.15. Such a method can produce a thin
film magnet having a high residual magnetization or coercive force
and thus a maximum energy product greater than 120 kJ/m.sup.3,
which is greater than that of bonded magnets or conventional thin
film magnets.
Further, according to the present invention, there is provided a
ferromagnetic thin film in a cylindrical form, which comprises a
substrate in a cylindrical or columnar form', and a perpendicular
magnetization film deposited on the side wall of the substrate',
the ferromagnetic thin film having radial anisotropic magnetic
properties. That is, there is provided, without the need for
machining processes, a ferromagnetic thin film in cylindrical form
with radial anisotropic magnetic properties that only has small
deviations on the order of microns from an ideal circular shape and
having radial dimensional accuracy of a similar order.
In addition, according to the present invention, there is provided
a method for producing a ferromagnetic thin film in a cylindrical
form having radial anisotropic magnetic properties by means of
physical vapor deposition, the method including the steps of;
heating a substrate in a cylindrical or columnar form to a
predetermined temperature', and depositing a perpendicular
magnetization film on the side wall of the substrate at a
predetermined deposition rate and at a predetermined gas pressure.
Such a method can produce a ferromagnetic thin film in a
cylindrical form having high radially anisotropic magnetic
properties, that is of a small size on the order of a millimeter or
even less with high dimensional accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross-sectional view that illustrates a film
deposition apparatus for producing a thin film magnet according to
an embodiment of the present invention;
FIG. 2 shows a cross-sectional view that illustrates another film
deposition apparatus for producing a thin film magnet according to
the present invention;
FIG. 3 shows a cross-sectional view that illustrates still another
film deposition apparatus for producing a thin film magnet
according to the present invention;
FIG. 4 shows a cross-sectional view that illustrates another film
deposition apparatus for producing a thin film magnet according to
the present invention;
FIG. 5 shows a cross-sectional view that illustrates the film
deposition apparatus of FIG. 4 taken along line A-A';
FIG. 6 shows a diagram that illustrates an X-ray diffraction
pattern of a thin film magnet according to the present
invention;
FIG. 7 shows a graph that illustrates the dependence of the
magnetic characteristics of the thin film magnets obtained in
Example 3 upon the substrate temperature according to the present
invention;
FIG. 8 shows a graph that illustrates the dependence of the
magnetic characteristics of the thin film magnets obtained in
Example 4 upon the deposition rate according to the present
invention;
FIG. 9 shows a graph that illustrates the dependence of the
magnetic characteristics of the thin film magnets obtained in
Example 5 upon the Ar gas pressure according to the present
invention;
FIG. 10 shows a cross-sectional view that illustrates an embodiment
of a ferromagnetic thin film in a cylindrical form according to the
invention;
FIG. 11 shows a cross-sectional view that illustrates another
embodiment of a ferromagnetic thin film in a cylindrical form
according to the invention;
FIG. 12 shows a cross-sectional view that illustrates another
embodiment of a ferromagnetic thin film in a cylindrical form
according to the invention;
FIG. 13 shows a cross-sectional view that illustrates another
embodiment of a ferromagnetic thin film in a cylindrical form
having a buffer layer according to the invention;
FIG. 14 shows a cross-sectional view that illustrates a film
deposition apparatus for producing a ferromagnetic thin film in a
cylindrical form according to the present invention;
FIG. 15 shows a cross-sectional view that illustrates the apparatus
of FIG. 14 taken along line B-B';
FIG. 16 shows a cross-sectional view that illustrates another film
deposition apparatus for producing a ferromagnetic thin film in a
cylindrical form according to the present invention;
FIG. 17 shows a cross-sectional view that illustrates still another
film deposition apparatus for producing a ferromagnetic thin film
in a cylindrical form according to the present invention;
FIG. 18 shows a cross-sectional view that illustrates another film
deposition apparatus for producing a ferromagnetic thin film in a
cylindrical form according to the present invention; and
FIG. 19 shows a diagram that illustrates an X-ray diffraction
pattern of the ferromagnetic thin film in a cylindrical form
obtained in Example 7 according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in further detail below
referring to preferred embodiments of thin film magnets,
cylindrical ferromagnetic thin films, and production methods
thereof, in conjunction with the accompanying drawings. In the
figures which will be referred to later, the same reference
numerals denote similar or corresponding elements.
FIG. 1 is a cross-sectional view that illustrates a film deposition
apparatus for producing a thin film magnet embodying the present
invention. As shown in FIG. 1, there is provided a boat 2 in a
vacuum chamber 1 so that a film deposition mechanism is disposed on
the boat 2. In FIG. 1, the film deposition mechanism is a
sputtering mechanism including a cathode electrode 3, a 3-inch
target 4, and a shutter plate 5 that can be opened and closed. A
substrate holder 6 is disposed at a position opposite the target 4.
A 2-inch substrate 7 is attached together with a mask 8 to the
substrate holder 6. There is also provided a heater 9 capable of
heating the substrate 7 up to about 800.degree. C.
Using this film deposition apparatus, a thin film magnet can be
formed on the substrate 7, according to the invention as described
below. The target 4 may be, for example, an (Nd, R)--M--B alloy.
After evacuating the vacuum chamber 1 to a sufficiently low
pressure using a pumping system 10, deposition gas, e.g., Ar gas,
is introduced into the vacuum chamber 1 via a valve 11. Target 4 is
then electrically discharged to initiate sputtering thereby forming
a thin film magnet on the substrate 7. If the mask 8 is used, a
thin film magnet is formed through the mask 8 only in the certain
predetermined areas on the substrate 7. When the shutter 5 is
closed, no film is deposited on the substrate 7. The power applied
to the target 4, the Ar gas pressure, and the temperature of the
substrate 7 can be precisely controlled by a power controller 12, a
mass flow controller 13, and a temperature controller 14,
respectively.
Instead of employing as the film deposition technique as sputtering
in the above example, vacuum evaporation may also be employed. In
the case that vacuum evaporation is employed, as shown in FIG. 2,
an evaporation source 15 is disposed on the boat 2, and a source
material such as an (Nd, R)--M--B alloy is heated so that the
source material is evaporated and thus a film is deposited onto a
substrate 7. A film similar to that obtained by the sputtering
technique may also be obtained using a laser ablation technique as
described below. As shown in FIG. 3, a laser beam is emitted by a
laser source 16 and passed through a slit 17. The laser beam is
then focused onto a target 4 via a lens 18 to ablate the (Nd,
R)--M--B alloy target 4 which is rotated by a target rotating
mechanism 19 and thus form a film on a substrate 7. As described
above, the thin film magnet according to the present invention may
be formed by using a physical deposition technique such as
sputtering, vacuum evaporation, laser ablation, etc.
Whereas a single deposition source is employed in the examples
mentioned above, a film may also be formed using a plurality of
deposition sources in a similar manner. FIG. 4 is a horizontal
cross-sectional view of a representative film deposition apparatus
example including a plurality of targets that can be sputtered at
the same time. FIG. 5 is a cross-sectional view of the apparatus
shown in FIG. 6 taken along line A-A'. As shown in FIGS. 4 and 5,
three cathode electrodes 3a, 3b, and 3c are disposed in a vacuum
chamber 1. A rotating substrate holder 20 is disposed at a central
position of the vacuum chamber 1 wherein up to 6 pieces of 2-inch
substrates 7 can be attached to the holder 20. 3-inch targets 4a,
4b, and 4c are attached to the respective cathode electrodes 3a,
3b, and 3c so that these targets 4a, 4b, and 4c can be discharged
at the same time while the rotating substrate holder 20 is rotated
by a motor 21, thereby sputtering these targets and forming a thin
film having a composition which is a mixture of the compositions of
these targets.
The cathode electrodes 3a, 3b, 3c are connected to separate power
controllers 12a, 12b, 12c, respectively, so that the power applied
to these targets 4a, 4b, and 4c can be controlled independently by
the power controllers 12a, 12b, and 12c. This allows deposition of
a thin film having various compositions. Deposition gas used for
film deposition is introduced into a vacuum chamber 1 via a valve
11 wherein the flow rate of the gas is controlled by a mass flow
controller 13. The substrates 7 are heated by heaters 9 disposed
inside the rotating substrate holder 20 while the temperatures of
the substrates 7 are controlled by a temperature controller 14.
Shutters 5a, 5b, and 5c, that can be opened and closed, are
disposed between the rotating substrate holder 20 and the
respective targets 4a, 4b, and 4c. Thus, when a shutter is closed,
no source material corresponding to the closed shutter is deposited
on the substrates 7 even during a sputtering process. This
deposition apparatus makes it possible to separately control the
composition of a ternary system. Thus, it is possible to easily
control the composition of the thin film magnet such as the
(Nd.sub.1-x R.sub.x) .sub.y M.sub.1-y-z B.sub.z thin film magnet
according to the present invention.
When the resultant composition of the thin film produced in the
physical vapor deposition method described above is in a certain
composition range including the composition of the (Nd.sub.1-x
R.sub.z).sub.y M.sub.1-y-z B.sub.z alloy being in the ranges of
0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15, wherein R is at least one element
selected from the group consisting of Tb, Ho, and Dy and M is Fe
metal or an Fe-based alloy including at least one element selected
from the group consisting of Co and Ni, the thin film includes an
Nd.sub.2 Fe.sub.14 B-based ferromagnetic phase as a main phase, and
the C-axis of the obtained crystal is oriented normal to the
deposition film plane so that the film becomes a perpendicular
magnetization film having a strong magnetic anisotropy in the
normal direction to the film plane. If the film is formed so that
the resultant composition is within the composition range
exemplified above, the film has residual magnetization and coercive
force greater than bonded magnets or conventional thin film magnets
and thus the film has a maximum energy product greater than 120
kJ/m.sup.3.
Whereas the film deposition may be performed at any substrate
temperature greater than the crystallization temperature, it is
preferable that the substrate temperature may be in the range in
which the deposited film has a stable Nd.sub.2 Fe.sub.14 B-based
ferromagnetic phase and the C-axis of the obtained crystal be
oriented perpendicular to the film plane. By way of example, Table
1 shows material characteristics of (Nd.sub.0.93
Tb.sub.0.07).sub.0.13 Fe.sub.0.76 B.sub.0.11 thin films
(crystallization temperature: 480.degree. C.) deposited at various
substrate temperatures. As an be seen from this table, if a film is
deposited at a substrate temperature in the range of about
500.degree.to 630.degree. C. which is higher than the
crystallization temperature, the film includes an Nd.sub.2
Fe.sub.14 B-based ferromagnetic phase as a main phase and the
C-axis of the crystal is oriented perpendicular to the film plane.
Thus, it is possible to obtain a thin film having a high maximum
energy product.
TABLE 1
__________________________________________________________________________
MAXIMUM MAXIMUM SUB. ENERGY ENERGY TEMP. MAIN C-AXIS PRODUCT
CRYSTALLI- MAIN C-AXIS MAXIMUM SAMPLE (.degree. C.) PHASE ORIENT.
(kJ/m.sup.3) ZATION PHASE ORIENT. (kJ/m.sup.3)
__________________________________________________________________________
1 300 amorphous x .ltoreq.1 530.degree. C. .times. 30 min Nd.sub.2
Fe.sub.14 B x 68 type crystal 2 400 amorphous x .ltoreq.1
530.degree. C. .times. 30 min Nd.sub.2 Fe.sub.14 B x 73 type
crystal 3 420 amorphous x .ltoreq.1 530.degree. C. .times. 30 min
Nd.sub.2 Fe.sub.14 B .smallcircle. 158 type crystal 4 480 amorphous
x .ltoreq.1 530.degree. C. .times. 30 min Nd.sub.2 Fe.sub.14 B
.smallcircle. 166 type crystal 5 500 Nd.sub.2 Fe.sub.14 B
.smallcircle. 165 -- -- -- -- type crystal 6 550 Nd.sub.2 Fe.sub.14
B .smallcircle. 174 -- -- -- -- type crystal 7 600 Nd.sub.2
Fe.sub.14 B .smallcircle. 163 -- -- -- -- type crystal 8 630
Nd.sub.2 Fe.sub.14 B .smallcircle. 155 -- -- -- -- type crystal 9
700 Nd.sub.2 Fe.sub.14 B x 97 -- -- -- -- type crystal
__________________________________________________________________________
In the case of Sample 4 shown in Table 1, since the film was
deposited at a temperature near the crystallization temperature,
the film did not crystallize well and thus the film included an
amorphous phase as a main phase. However, even in this case, if a
crystallization treatment is performed on the film by heating the
film in an electric furnace or the like at a temperature higher
than the crystallization temperature thereby crystallizing the film
into an Nd.sub.2 Fe.sub.14 B-based ferromagnetic phase, it is
possible to obtain a perpendicular magnetization film. As in the
case of Sample 3, even when the film is deposited at a temperature
lower than the crystallization temperature, if the temperature
difference is less than 60.degree. C., it is possible to obtain a
perpendicular magnetization film by performing a crystallization
treatment. This results in a thin film having a high maximum energy
product similar to that of a thin film deposited at a temperature
in the range from 500.degree. C. to 630.degree. C. However, if the
film is deposited at a substrate temperature 80.degree. C. or more
lower than the crystallization temperature, the C-axis of the
crystal will no longer be oriented in a direction across the film
thickness even after a crystallization treatment is performed.
Thus, in this case, the resultant thin film will show isotropic
magnetic properties. On the other hand, if a film is deposited at a
temperature higher than 700.degree. C., the orientation of the
C-axis of the crystal is disturbed. For this reason, extremely high
substrate temperatures are undesirable.
According to the present invention, as described above, it is
possible to produce a high-quality thin film magnet even at a
substrate temperature lower than the crystallization temperature by
performing a crystallization treatment. This allows a thin film
magnet to be deposited over a very wide range of temperatures.
In Table 1, the orientation of the C-axis is evaluated according to
the criterion that if the X-ray diffraction pattern of the thin
magnet shown in FIG. 6 has a ratio .[..SIGMA.I.sub.00m)
+I.sub.(105) /.SIGMA.I,.]. .Iadd..SIGMA.I.sub.(00m)
+I.sub.(105))/.SIGMA.I, .Iaddend.that is the ratio of the sum of
the C-plane peak intensity I.sub.(00m) (m=4, 6, 8 or 10) and the
(105) peak intensity I.sub.(105) to the total peak intensity
.SIGMA.I of the Nd.sub.2 Fe.sub.14 B-based compound, greater than
0.9, then the orientation is regarded as good (o), and regarded as
bad (x) in the opposite case. This criterion will also be employed
in Tables 2, 3, and 4 described later.
As for the deposition rate, it is possible to form a film at a few
.mu.m/hr without any problems as in the case of the deposition of
conventional magnetic thin films.
However, as can be seen from Table 2 showing the material
characteristics of (Nd.sub.0.93 Tb.sub.0.07).sub.0.13 Fe.sub.0.76
B.sub.0.11 thin films, if a film is deposited at a deposition rate
of 40 .mu.m/hr or more, the orientation of the C-axis of the
crystal is degraded, and thus such a high deposition rate is
undesirable.
TABLE 2 ______________________________________ DEPOSITION C-AXIS
MAXIMUM ENERGY SAMPLE RATE (.mu.m/hr) ORIENTATION PRODUCT
(kI/m.sup.3) ______________________________________ 1 0.05
.smallcircle. 162 2 0.1 .smallcircle. 169 3 0.5 .smallcircle. 170 4
1.0 .smallcircle. 172 4 .smallcircle. 170 6 8.0 .smallcircle. 166 7
10.0 .smallcircle. 165 8 20.0 .smallcircle. 160 9 40.0 X 86
______________________________________
The substrate material of the invention is not particularly
limited. As can be seen from Table 3, an (Nd.sub.0.93 Tb.sub.0.07)
.sub.0.13 Fe.sub.0.76 B.sub.0.11 thin film having good
characteristics can be deposited on various types of substrates
such as glass, metal, alloy oxides, nitrides, etc. In Table 3, the
term "sputtered film" denotes a substrate of the type that was
obtained by sputtering Fe, Fe--Si, Fe--Co, or Fe--Ni on a quartz
glass substrate.
TABLE 3
__________________________________________________________________________
SUBSTRATE SUBSTRATE TYPE C-AXIS MAXIMUM ENERGY SAMPLE MATERIAL
(thickness) ORIENTATION PRODUCT (kJ/m.sup.3)
__________________________________________________________________________
1 quartz glass bulk (0.5 mm) .smallcircle. 165 2 Si single crystal
wafer (0.35 mm) .smallcircle. 161 3 Al.sub.2 O.sub.3 bulk (0.8 mm)
.smallcircle. 163 4 MgO bulk (0.8mm) .smallcircle. 166 5 TiN bulk
(0.8 mm) .smallcircle. 170 6 W bulk (0.5 mm) .smallcircle. 169 7 Fe
sputtered film (0.2 .mu.m) .smallcircle. 161 8 Fe--Si sputtered
film (0.2 .mu.m) .smallcircle. 160 9 Fe--Co sputtered film (0.2
.mu.m) .smallcircle. 167 10 Fe--Ni sputtered film (0.2 .mu.m)
.smallcircle. 159
__________________________________________________________________________
When a film is deposited using the sputtering technique, the gas
pressure during a deposition process may be in the range of from a
few mm Pa to a few Pa without any problems as in common techniques
for depositing magnetic thin films. However, as can be seen from
Table 4 showing the material characteristics of (Nd.sub.0.93
Tb.sub.0.07).sub.0.13 Fe.sub.0.76 B.sub.0.11 thin films, if a film
is deposited at a gas pressure of 40 Pa, the orientation of the
C-axis of the crystal is degraded. Thus, too high a gas pressure is
undesirable.
TABLE 4 ______________________________________ Ar GAS PRESSURE
C-AXIS MAXIMUM ENERGY SAMPLE (Pa) ORIENTATION PRODUCT (kI/m.sup.3)
______________________________________ 1 0.05 .smallcircle. 170 2
0.50 .smallcircle. 168 3 2.00 .smallcircle. 169 4 5.00
.smallcircle. 166 5 8.00 .smallcircle. 165 6 20.0 .smallcircle. 161
7 40.0 X 92 ______________________________________
Referring now to specific examples, the present invention will be
described in further detail below.
EXAMPLE 1
In the film deposition apparatus shown in FIG. 4, Nd--R (R is Tb,
Ho, or Dy) serving as the target 4a, Fe metal as the target 4b, and
an FeB alloy as the target 4c were attached to the cathode
electrodes 3a, 3b, and 3c, respectively. The target 4a was made in
such a manner that R metal chips having dimensions of 5 mm.times.5
mm.times.1 mm (thickness) was disposed on a 3 inch diameter Nd
metal target. A 12 mm.times.12 mm.times.0.5 mm (thickness) quartz
glass substrate was attached to the rotating substrate holder 20.
The inside of the vacuum chamber 1 was then evacuated to a pressure
less than 1.times.10.sup.-4 Pa via the pumping system 10. The
substrate 7 was then heated by the heater 9 up to 590.degree.
C.
After the temperature of the substrate 7 became stable, Ar gas was
introduced into the vacuum chamber 1, and the gas pressure was
maintained at 8 Pa. Substrate holder 20 was rotated by the motor
21. While maintaining the shutters 5a, 5b, and 5c in a closed
state, voltages were applied to the targets 4a, 4b, and 4c to
discharge these targets. Under this condition, the targets were
sputtered for 5 to 15 minutes so as to remove the oxides present on
the surfaces of the targets. The shutters 5a, 5b, and 5c were then
opened and thus film deposition onto the substrate 7 was begun. The
film deposition was performed at a deposition rate of 8 .mu.m/hr
for a predetermined time period. After the completion of the film
deposition, the discharging of the targets, the supplying of Ar
gas, and the heating of the substrate by means of the heater were
all stopped simultaneously. While evacuating the inside of the
vacuum chamber 1, the sample remaining in the vacuum chamber 1 was
cooled at a slow cooling rate. Thus, a thin film of (Nd.sub.1-x
Tb.sub.x).sub.y Fe.sub.1-y-z B.sub.z having a thickness of about 2
.mu.m was obtained.
The composition of the thin film magnet was controlled by
separately adjusting the power applied to each target so that
desired values were obtained for y and z in the composition formula
and also by adjusting the number of R chips so that x had a desired
value.
Table 5 shows the magnetic characteristics measured perpendicular
to the film plane for obtained (Nd.sub.1-x Tb.sub.x).sub.y
Fe.sub.1-y-z B.sub.z thin film magnets, wherein, R was Tb.
TABLE 5
__________________________________________________________________________
RESIDUAL COERCIVE MAXIMUM ENERGY SAMPLE COMPOSITION MAGNETIZATION
(T) FORCE (kA/m) PRODUCT (kJ/m.sup.3)
__________________________________________________________________________
1 (Nd.sub.0.96 Tb.sub.0.04).sub.0.11 Fe.sub.0.81 B.sub.0.08 1.09
528 156 2 (Nd.sub.0.96 Tb.sub.0.04).sub.0.11 Fe.sub.0.74 B.sub.0.15
1.00 712 143 3 (Nd.sub.0.96 Tb.sub.0.04).sub.0.13 Fe.sub.0.76
B.sub.0.11 1.03 672 161 4 (Nd.sub.0.96 Tb.sub.0.04).sub.0.15
Fe.sub.0.77 B.sub.0.08 1.02 600 145 5 (Nd.sub.0.96
Tb.sub.0.04).sub.0.15 Fe.sub.0.70 B.sub.0.15 0.92 768 128 6
(Nd.sub.0.93 Tb.sub.0.07).sub.0.11 Fe.sub.0.81 B.sub.0.08 1.06 624
194 7 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 Fe.sub.0.78 B.sub.0.11
1.02 696 170 8 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 Fe.sub.0.74
B.sub.0.15 0.97 800 157 9 (Nd.sub.0.93 Tb.sub.0.07).sub.0.13
Fe.sub.0.79 B.sub.0.08 1.02 656 184 10 (Nd.sub.0.93
Tb.sub.0.07).sub.0.13 Fe.sub.0.76 B.sub.0.11 1.00 736 165 11
(Nd.sub.0.93 Tb.sub.0.07).sub.0.13 Fe.sub.0.72 B.sub.0.15 0.93 832
149 12 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15 Fe.sub.0.71 B.sub.0.08
1.00 688 172 13 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15 Fe.sub.0.74
B.sub.0.11 0.97 768 157 14 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15
Fe.sub.0.70 B.sub.0.15 0.88 840 141 15 (Nd.sub.0.90
Tb.sub.0.10).sub.0.11 Fe.sub.0.81 B.sub.0.08 1.01 656 153 16
(Nd.sub.0.90 Tb.sub.0.10).sub.0.11 Fe.sub.0.74 B.sub.0.15 0.91 840
132 17 (Nd.sub.0.90 Tb.sub.0.10).sub.0.13 Fe.sub.0.76 B.sub.0.11
0.95 760 144 18 (Nd.sub.0.90 Tb.sub.0.10).sub.0.15 Fe.sub.0.77
B.sub.0.08 0.94 704 135 19 (Nd.sub.0.90 Tb.sub.0.10).sub.0.15
Fe.sub.0.70 B.sub.0.15 0.86 880 133 COMP. 1 Nd--Fe--B based bonded
0.70 400 90 COMP. 2 Nd--Fe--B based bonded 0.79 840 105 COMP. 3
Nd--Fe--B based bonded 0.69 740 85 COMP. 4 Nd.sub.0.11 Fe.sub.0.81
B.sub.0.08 1.12 248 71 COMP. 5 Nd.sub.0.11 Fe.sub.0.74 B.sub.0.15
1.04 544 132 COMP. 6 Nd.sub.0.13 Fe.sub.0.76 B.sub.0.11 1.03 336
116 COMP. 7 Nd.sub.0.15 Fe.sub.0.77 B.sub.0.08 1.05 280 85 COMP. 8
Nd.sub.0.15 Fe.sub.0.70 B.sub.0.15 0.94 600 119 COMP. 9 Nd.sub.0.19
Fe.sub.0.63 B.sub.0.18 0.68 902 62 COMP. 10 (Nd.sub.0.98
Tb.sub.0.02).sub.0.11 Fe.sub.0.81 B.sub.0.08 1.10 336 106 COMP. 11
(Nd.sub.0.98 Tb.sub.0.02).sub.0.11 Fe.sub.0.74 B.sub.0.15 1.02 608
143 COMP. 12 (Nd.sub.0.98 Tb.sub.0.02).sub.0.13 Fe.sub.0.76
B.sub.0.11 1.04 424 131 COMP. 13 (Nd.sub.0.98 Tb.sub.0.02).sub.0.15
Fe.sub.0.77 B.sub.0.08 1.04 312 95 COMP. 14 (Nd.sub.0.98
Tb.sub.0.02).sub.0.15 Fe.sub.0.70 B.sub.0.15 0.93 648 127 COMP. 15
(Nd.sub.0.85 Tb.sub.0.15).sub.0.11 Fe.sub.0.81 B.sub.0.08 0.98 696
144 COMP. 16 (Nd.sub.0.85 Tb.sub.0.15).sub.0.11 Fe.sub.0.74
B.sub.0.15 0.87 872 113 COMP. 17 (Nd.sub.0.85 Tb.sub.0.15).sub.0.13
Fe.sub.0.76 B.sub.0.11 0.89 800 123 COMP. 18 (Nd.sub.0.85
Tb.sub.0.15).sub.0.15 Fe.sub.0.77 B.sub.0.08 0.88 736 108 COMP. 19
(Nd.sub.0.85 Tb.sub.0.15).sub.0.15 Fe.sub.0.70 B.sub.0.15 0.77 920
91 COMP. 20 (Nd.sub.0.93 Tb.sub.0.07).sub.0.09 Fe.sub.0.85
B.sub.0.06 1.02 72 23 COMP. 21 (Nd.sub.0.93 Tb.sub.0.07).sub.0.09
Fe.sub.0.83 B.sub.0.08 0.96 72 22 COMP. 22 (Nd.sub.0.93
Tb.sub.0.07).sub.0.09 Fe.sub.0.80 B.sub.0.11 0.89 80 25 COMP. 23
(Nd.sub.0.93 Tb.sub.0.07).sub.0.09 Fe.sub.0.76 B.sub.0.15 0.86 240
43 COMP. 24 (Nd.sub.0.93 Tb.sub.0.07).sub.0.09 Fe.sub.0.74
B.sub.0.17 0.85 200 32 COMP. 25 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11
Fe.sub.0.83 B.sub.0.06 1.07 208 52 COMP. 26 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 Fe.sub.0.72 B.sub.0.17 0.84 680 95 COMP. 27
(Nd.sub.0.93 Tb.sub.0.07).sub.0.13 Fe.sub.0.81 B.sub.0.06 1.04 232
61 COMP. 28 (Nd.sub.0.93 Tb.sub.0.07).sub.0.13 Fe.sub.0.70
B.sub.0.17 0.80 696 96 COMP. 29 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15
Fe.sub.0.79 B.sub.0.06 1.00 256 71 COMP. 30 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 Fe.sub.0.68 B.sub.0.17 0.73 704 77 COMP. 31
(Nd.sub.0.93 Tb.sub.0.07).sub.0.17 Fe.sub.0.77 B.sub.0.06 0.88 360
85 COMP. 32 (Nd.sub.0.93 Tb.sub.0.07).sub.0.17 Fe.sub.0.75
B.sub.0.08 0.86 600 108 COMP. 33 (Nd.sub.0.93 Tb.sub.0.07).sub.0.17
Fe.sub.0.72 B.sub.0.11 0.79 704 96 COMP. 34 (Nd.sub.0.93
Tb.sub.0.07).sub.0.17 Fe.sub.0.68 B.sub.0.15 0.72 760 84 COMP. 35
(Nd.sub.0.93 Tb.sub.0.07).sub.0.17 Fe.sub.0.66 B.sub.0.17 0.67 840
73
__________________________________________________________________________
As can be seen from Table 5, the samples according to the present
invention all show high coercive force and residual magnetization
and thus high maximum energy products of 128 to 194 kJ/m.sup.3 in
the composition ranges of 0.04.ltoreq.x.ltoreq.0.10,
0.11.ltoreq.y.ltoreq.0.15, and 0.08.ltoreq.z.ltoreq.0.15. These
values are greater than those of bonded magnets which are also
shown in Table 5 as Comparative Samples 1 to 3 and greater than
those of conventional Nd-Fe-B thin film magnets shown as
Comparative Samples 4 to 9. However, if the composition x fails to
fall within the range of 0.04.ltoreq.x.ltoreq.0.10 specified by the
present invention, the maximum energy product more than 120
kJ/m.sup.3 is not always obtained as in the case of Comparative
Samples 10 to 19 where x=0.02 or x=0.15.
In the case of samples where x=0.02, though slight improvement was
found compared with that of the conventional thin film magnets,
their coercive force was still not sufficient and thus it is not
possible to obtain a maximum energy product greater than 120
kJ/m.sup.3 for some samples.
On the other hand, in the case of the samples where x=0.15, though
they have a sufficient coercive force, a great reaction occurs in
residual magnetization. As a result, it is difficult to obtain a
maximum energy product greater than 120 kJ/m.sup.3 for some
samples. Furthermore, even in the case where
0.04.ltoreq.x.ltoreq.0.10, if y and z values do not satisfy the
composition requirements 0.11.ltoreq.y.ltoreq.0.15 and
0.08.ltoreq.z.ltoreq.0.15, it is impossible to obtain a maximum
energy product greater than 120 kJ/m.sup.3 as in the case of
Comparative Samples 20 to 35. If the composition deviates from the
optimum range to low levels of Nd and B, .alpha.-Fe will be
precipitated in a film and thus it is impossible to obtain a
sufficient coercive force. On the other hand, if the composition
deviates from the optimum range to a high level of Nd, the
anisotropic magnetic properties perpendicular to the film plane of
thin film magnets are disturbed and thus both residual
magnetization and coercive force levels fall. In the case where the
composition deviates from the optimum range to a higher level of B,
a great reduction in residual magnetization occurs. To achieve a
maximum energy product greater than 120 kJ/m.sup.3, as can be seen
from the above discussion, the composition must be in the ranges of
0.04.ltoreq.x.ltoreq.0.10, 0.11.ltoreq.y.ltoreq.0.15, and
0.08.ltoreq.z.ltoreq.0.15. In the case Ho or Dy was used as R,
similar results were obtained (Data not shown).
EXAMPLE 2
The film deposition apparatus shown in FIG. 4 was used, and Nd--Tb,
M .[.fie--Co,.]. .Iadd.(Fe--Co, .Iaddend.Fe--Ni, or Fe--Co--Ni
alloy), and an FeB alloy were employed as the targets 4a, 4b, and
4c, repectively. (Nd.sub.0.93 Tb.sub.0.07).sub.y M.sub.1-y-z
B.sub.z thin film magnets having a thickness of about 2 .mu.m were
formed on quartz glass substrates according to a procedure similar
to that in Example 1 wherein the substrate temperature, the Ar gas
pressure, and the deposition rate were 590.degree. C. 8 Pa, and 8
.mu.m/hr, respectively.
Table 6 shows the resultant magnetic characteristics measured
perpendicular to the film plane for obtained thin film magnets. As
can be seen from Table 6, the films show magnetic characteristics
which are basically similar to those of the (Nd.sub.0.93
Tb.sub.0.07).sub.y Fe.sub.1-y-z B.sub.z thin film magnets described
above with slight differences in the magnetic characteristics being
observed depending on the changes in the Co and Ni compositions.
The results show that any of the Fe-based alloys including Fe--Co,
Fe--Ni, and Fe--Co--Ni may be employed as M to achieve a high
maximum energy product greater than 120 kJ/m.sup.3 as in the case
where Fe metal is employed.
TABLE 6
__________________________________________________________________________
RESIDUAL COERCIVE MAXIMUM ENERGY SAMPLE COMPOSITION MAGNETIZATION
(T) FORCE (kA/m) PRODUCT (kJ/m.sup.3)
__________________________________________________________________________
1 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 (Fe.sub.0.85
Co.sub.0.15).sub.0.81 B.sub.0.08 1.10 640 203 2 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 (Fe.sub.0.85 Co.sub.0.15).sub.0.74 B.sub.0.15
1.01 824 168 3 (Nd.sub.0.93 Tb.sub.0.07).sub.0.13 (Fe.sub.0.85
Co.sub.0.15).sub.0.76 B.sub.0.11 1.03 752 171 4 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 (Fe.sub.0.85 Co.sub.0.15).sub.0.77 B.sub.0.08
1.02 688 178 5 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15 (Fe.sub.0.85
Co.sub.0.15).sub.0.70 B.sub.0.15 0.92 856 149 6 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 (Fe.sub.0.70 Co.sub.0.30).sub.0.81 B.sub.0.08
1.05 632 196 7 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 (Fe.sub.0.70
Co.sub.0.30).sub.0.74 B.sub.0.15 0.98 808 160 8 (Nd.sub.0.93
Tb.sub.0.07).sub.0.13 (Fe.sub.0.70 Co.sub.0.30).sub.0.76 B.sub.0.11
0.98 720 165 9 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15 (Fe.sub.0.70
Co.sub.0.30).sub.0.77 B.sub.0.08 1.00 672 170 10 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 (Fe.sub.0.98 Co.sub.0.30).sub.0.70 B.sub.0.15
0.89 832 144 11 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 (Fe.sub.0.98
Ni.sub.0.02).sub.0.81 B.sub.0.08 1.05 632 189 12 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 (Fe.sub.0.98 Ni.sub.0.02).sub.0.74 B.sub.0.15
0.97 800 154 13 (Nd.sub.0.93 Tb.sub.0.07).sub.0.13 (Fe.sub.0.98
Ni.sub.0.02).sub.0.76 B.sub.0.11 0.99 728 162 14 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 (Fe.sub.0.98 Ni.sub.0.02).sub.0.77 B.sub.0.08
1.00 696 168 15 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15 (Fe.sub.0.98
Ni.sub.0.02).sub.0.70 B.sub.0.15 0.87 808 137 16 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 (Fe.sub.0.96 Ni.sub.0.04).sub.0.81 B.sub.0.08
1.03 648 180 17 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 (Fe.sub.0.96
Ni.sub.0.04).sub.0.74 B.sub.0.15 0.95 824 153 18 (Nd.sub.0.93
Tb.sub.0.07).sub.0.13 (Fe.sub.0.96 Ni.sub.0.04).sub.0.76 B.sub.0.11
0.97 712 158 19 (Nd.sub.0.93 Tb.sub.0.07).sub.0.15 (Fe.sub.0.96
Ni.sub.0.04).sub.0.77 B.sub.0.08 1.00 672 164 20 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 (Fe.sub.0.96 Ni.sub.0.04).sub.0.70 B.sub.0.15
0.86 864 133 21 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11 (Fe.sub.0.80
Co.sub.0.15 Ni.sub.0. 05).sub.0.81 B.sub.0.08 1.07 624 191 22
(Nd.sub.0.93 Tb.sub.0.07).sub.0.11 (Fe.sub.0.80 Co.sub.0.15
Ni.sub.0. 05).sub.0.74 B.sub.0.15 0.99 792 161 23 (Nd.sub.0.93
Tb.sub.0.07).sub.0.13 (Fe.sub.0.80 Co.sub.0.15 Ni.sub.0.
05).sub.0.76 B.sub.0.11 1.00 760 169 24 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 (Fe.sub.0.80 Co.sub.0.15 Ni.sub.0.
05).sub.0.77 B.sub.0.08 0.98 720 177 25 (Nd.sub.0.93
Tb.sub.0.07).sub.0.15 (Fe.sub.0.80 Co.sub.0.15 Ni.sub.0.
05).sub.0.70 B.sub.0.15 0.91 880 153
__________________________________________________________________________
EXAMPLE 3
The film deposition apparatus shown in FIG. 4 was used. Nd-Tb, Fe
metal, and an FeB alloy were employed as the targets 4a, 4b, and
4c, respectively, and (Nd.sub.1-x Tb.sub.x).sub.y Fe.sub.1-y-z
B.sub.z thin film magnets having a thickness of about 2 .mu.m were
formed on quartz glass substrates in a manner similar to that in
Example 1, wherein the substrate temperature, the Ar gas pressure,
and the deposition rate were 510.degree. to 590.degree. C. 8 Pa,
and 8 .mu.m/hr, respectively.
FIG. 7 shows the magnetic characteristics of the thin film magnets
obtained as a function of the substrate temperature upon. From FIG.
7, it can be seen that if a substrate temperature in the range from
530.degree. to 570.degree. C. is employed, it is possible to obtain
particularly high coercive force and thus a large maximum energy
product greater than at lease 140 kJ/m.sup.3.
EXAMPLE 4
In this example, (Nd.sub.1-x Tb.sub.x).sub.y Fe.sub.1-y--z B.sub.z
thin film magnets were formed in a manner similar to Example 3,
wherein the substrate temperature, the Ar gas pressure, and the
deposition rate were 590.degree. C., 8 Pa, and 0.05 to 20 .mu.m/hr,
respectively.
FIG. 8 shows the magnetic characteristics of the obtained thin film
magnets as a function of the deposition rate. As can be seen from
FIG. 8, if the deposition is performed at a deposition rate in the
range from 0.1 to 4 .mu.m/hr, it is possible to obtain particularly
high residual magnetization and thus a maximum energy product
greater than at least 140 kJ/m.sup.3.
EXAMPLE 5
In this example, (Nd.sub.1-x Tb.sub.x).sub.y Fe.sub.1-y-z B.sub.z
thin film magnets were formed in the same manner as in Example 3
except that the substrate temperature, the Ar gas pressure, and the
deposition rate were 590.degree. C., 0.05 to 20 Pa, 8 .mu.m/hr;
respectively.
FIG. 9 shows the magnetic characteristics of the obtained thin film
magnets as a function of the Ar gas pressure. As can be seen from
FIG. 9, if the deposition is performed at an Ar gas pressure in the
range from 0.05 to 4 Pa, it is possible to obtain particularly high
residual magnetization and thus a maximum energy product greater
than at least 140 kJ/m.sup.3.
EXAMPLE 6
(Nd.sub.1-x Tb.sub.x).sub.y Fe.sub.1-y-z B.sub.z thin film magnets
were formed in the same manner as in Example 3 except that the
substrate temperature, the Ar gas pressure, and the deposition rate
were 530.degree. to 570.degree. C., 0.05 to 4 Pa, 0.1 to 4
.mu.m/hr, respectively. The results are shown in Table 7.
TABLE 7
__________________________________________________________________________
SUBSTRATE Ar GAS DEPOSITION MAXIMUM ENERGY SAMPLE COMPOSITION TEMP.
(.degree. C.) PRESSURE (Pa) RATE (.mu.m/hr) PRODUCT (kJ/m.sup.3)
__________________________________________________________________________
1 (Nd.sub.0.96 Tb.sub.0.04).sub.0.11 Fe.sub.0.81 B.sub.0.08 530
0.05 4.0 182 2 (Nd.sub.0.96 Tb.sub.0.04).sub.0.13 Fe.sub.0.76
B.sub.0.11 530 0.05 4.0 195 3 (Nd.sub.0.96 Tb.sub.0.04).sub.0.15
Fe.sub.0.70 B.sub.0.15 530 0.05 4.0 166 4 (Nd.sub.0.90
Tb.sub.0.10).sub.0.31 Fe.sub.0.81 B.sub.0.08 530 4.0 0.1 187 5
(Nd.sub.0.90 Tb.sub.0.10).sub.0.13 Fe.sub.0.76 B.sub.0.11 530 4.0
0.1 176 6 (Nd.sub.0.90 Tb.sub.0.10).sub.0.15 Fe.sub.0.70 B.sub.0.15
530 4.0 0.1 165 7 (Nd.sub.0.96 Tb.sub.0.04).sub.0.11 Fe.sub.0.82
B.sub.0.08 570 0.05 0.1 188 8 (Nd.sub.0.96 Tb.sub.0.04).sub.0.13
Fe.sub.0.76 B.sub.0.11 570 0.05 0.1 199 9 (Nd.sub.0.96
Tb.sub.0.04).sub.0.15 Fe.sub.0.70 B.sub.0.15 570 0.05 0.1 168 10
(Nd.sub.0.90 Tb.sub.0.10).sub.0.11 Fe.sub.0.81 B.sub.0.08 570 4.0
4.0 187 11 (Nd.sub.0.90 Tb.sub.0.10).sub.0.13 Fe.sub.0.76
B.sub.0.11 570 4.0 4.0 175 12 (Nd.sub.0.90 Tb.sub.0.10).sub.0.15
Fe.sub.0.70 B.sub.0.15 570 4.0 4.0 164 13 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 Fe.sub.0.81 B.sub.0.08 550 2.0 4.0 204 14
(Nd.sub.0.93 Tb.sub.0.07).sub.0.11 Fe.sub.0.81 B.sub.0.08 550 2.0
0.1 208 15 (Nd.sub.0.95 Tb.sub.0.07).sub.0.11 Fe.sub.0.81
B.sub.0.08 550 0.05 2.0 220 16 (Nd.sub.0.93 Tb.sub.0.07).sub.0.11
Fe.sub.0.81 B.sub.0.08 550 4.0 2.0 215 17 (Nd.sub.0.93
Tb.sub.0.07).sub.0.11 Fe.sub.0.81 B.sub.0.08 530 2.0 2.0 212 18
(Nd.sub.0.93 Tb.sub.0.07).sub.0.11 Fe.sub.0.81 B.sub.0.08 570 2.0
2.0 204 19 (Nd.sub.0.93 Tb.sub.0.07).sub.0.12 Fe.sub.0.81
B.sub.0.08 550 2.0 2.0 214 COMP. 1 (Nd.sub.0.96
Tb.sub.0.04).sub.0.15 Fe.sub.0.70 B.sub.0.15 600 2.0 2.0 150 COMP.
2 (Nd.sub.0.96 Tb.sub.0.04).sub.0.15 Fe.sub.0.70 B.sub.0.15 550 8.0
2.0 156 COMP. 3 (Nd.sub.0.96 Tb.sub.0.04).sub.0.15 Fe.sub.0.70
B.sub.0.15 550 2.0 8.0 151
__________________________________________________________________________
As can be seen from Table 7, if the film on conditions are limited
to within the ranges described above, it is possible to obtain very
high coercive force and residual magnetization and thus a maximum
energy product greater than at least 160 kJ/m.sup.3. However, if
the deposit conditions are not limited to within these ranges, it
is impossible to obtain a maximum energy product greater than 160
kJ/m.sup.3 as in the case of Comparative Samples 1 to 3.
Now, referring to the accompanying drawings, a cylindrical
ferromagnetic thin film having radial anisotropy according to the
present invention will be described below.
FIG. 10 is a cross-sectional view of an embodiment of a cylindrical
ferromagnetic thin film having radial anisotropy according to the
invention. As shown in FIG. 10, a perpendicular magnetization film
23 is formed on the side wall of a columnar substrate 22. A
cylinder may also be used as the substrate. In this case, a
perpendicular magnetization film 23 may be deposited on either the
outer side wall or the inner side wall of the cylindrical substrate
24 as shown in FIGS. 11 and 12. Alternatively, the cylindrical
substrate may be removed after film deposition, so as to obtain a
cylindrical ferromagnetic thin film consisting of only the
deposited film.
The present invention does not particularly limit the thin film
material as long as the material has strong a anisotropic magnetic
properties in the direction across the film thickness. Not only
rare earth element-transition metal alloys, but also other various
materials for example magnetic recording materials such as
Co--Cr-based alloys and Ba-based ferrites, magneto-optic recording
materials such as MnBi-based alloys and rare earth
element-transition metal amorphous alloys are employed. More
specifically, if (Nd, R)--M--B alloys are used as the thin film
material, it is possible to obtain a cylindrical thin fill magnet
having radial anisotropy and also having a large maximum energy
product. As for the substrate material, various materials such as
glass, metal, alloys, oxides, and nitrides may be employed without
particular limitations.
Furthermore, if a buffer layer 25 is formed between the substrate
and the thin film as shown in FIG. 13, it is possible to improve
adhesion between the substrate and the thin film, and the radial
anisotropy of the thin film is also improved. Whereas a material in
a columnar form is used as the substrate in the example shown in
FIG. 13, the buffer layer 25 may also be employed for the same
purpose in the case where the substrate is in the cylindrical form.
The invention has no particular limitation in the method of forming
the thin film on the side wall of the substrate in the cylindrical
or columnar form, as long as the method allows formation of a
perpendicular magnetization film. Specific examples include
sputtering, vacuum evaporation, and laser ablation techniques.
Referring now to a particular embodiment, the invention will be
described in further detail below.
FIG. 14 shows a cross-sectional view of a film deposition apparatus
for producing a cylindrical ferromagnetic thin film with radial
anisotropy, embodying the present invention. FIG. 15 shows a
cross-sectional view of the apparatus shown in FIG. 14 taken along
line B-B'. As shown in FIGS. 14 and 15, there is provided a boat 2
in a vacuum chamber 1 so that a film deposition mechanism is
disposed on the boat 2. In the example shown in FIGS. 14 and 15,
the film deposition mechanism is a sputtering mechanism including a
cathode electrode 3, a 3 inch diameter target 4, and a shutter
plate 5 that can be opened and closed. A holder 26 for holding a
columnar substrate is disposed at a central position of the vacuum
chamber 1 wherein a columnar substrate 22 having a diameter of 0.1
mm to 20 mm and a length of 10 mm to 100 mm can be attached to the
holder 26. The substrate holder 26 can be rotated by a motor
21.
There is also provided a heater 27 for heating the columnar
substrate. As for the heating method, either infrared heating or
induction heating may be employed depending on the film material
and the substrate material. Otherwise, a combination of infrared
heating and induction heating may also be employed. Using this film
deposition apparatus, a perpendicular magnetization thin film 23 is
formed as follows. Deposition gas is introduced into the vacuum
chamber 1 via a valve 11. The target 4 is then discharged while
rotating the substrate holder 26 to which the columnar substrate 22
is attached thereby sputtering the target 4 and thus forming a
perpendicular magnetization thin film 23 having a uniform
composition and a uniform thickness on the side wall of the
columnar substrate 22. If a mask 8 is used, the thin film is formed
via the mask 8 only in the desired areas on the columnar substrate
22. When the shutter 5 is closed, no film is deposited on the
columnar substrate 22. The power applied to the target, the Ar gas
pressure, and the substrate temperature are precisely controlled by
a power controller 12, a mass flow controller 13, and a temperature
controller 14, respectively.
Whereas sputtering is employed as the film deposition technique in
the above example, a vacuum evaporation technique may also be
employed for the same purpose. In this case, an evaporation source
15 is put on the boat 2 as shown in FIG. 16. Furthermore, a laser
ablation technique may also be employed for the same purpose. In
this case, as shown in FIG. 17, a laser beam is emitted by a laser
source 16 and passed through a slit 17. The laser beam is then
focused onto a target 4 via a lens 18 thereby ablating the target 4
which is rotated by a target rotating mechanism 19 and thus forming
a film on a columnar substrate 22. Although a columnar substrate 22
was employed in the above example, it is also possible to deposit a
film on the outer side wall in the case wherein the cylindrical
substrate 24 is employed.
It is also possible to deposit a film on the inner side of the
cylindrical substrate 24. In this case, an apparatus such as that
shown in FIG. 18 having a sputtering chamber 28 and a nozzle 29
inside a vacuum chamber 1 is used. The nozzle 29 is inserted into
the cylindrical substrate 24, and the cylindrical substrate 24 is
rotated. Under this condition, if the shutter plate 5 is opened,
sputtered substances are ejected through the nozzle 29 onto the
inner side wall of the cylindrical substrate 24 thereby depositing
a film thereon. A mask 30 may be used to deposit the film only on
the desired areas of the inner side wall of the cylindrical
substrate 24. The ejection rate of the sputtered substances through
the nozzle 29 can be controlled by adjusting the evacuation
conductance via a variable valve 31 disposed in the sputtering
chamber 28.
EXAMPLE 7
The film deposition apparatus shown in FIG. 14 was employed, and a
sintered alloy of Nd--Fe--B serving as the target 4 was attached to
the cathode electrode 3. A cylindrical or columnar WC (tungsten
carbide) substrate having an outer diameter of 3 mm or 0.9 mm and a
length of 30 mm was then attached to the substrate holder 26. The
inside of the vacuum chamber 1 was then evacuated to a pressure
less than 1.times.10.sup.-4 Pa via a pumping system 10. The WC
substrate was then heated by the heater 27.degree. to 560.degree.
C. After the temperature of the substrate became stable, Ar gas was
introduced into the vacuum chamber 1, so that the gas pressure was
maintained at 1 Pa. The substrate holder 26 was rotated by the
motor 21. While maintaining the shutter plate 5 in a closed state,
a voltage was applied to the target 4 to initiate discharging of
the target. Under this condition, the target was sputtered for 5 to
15 minutes so as to remove the oxide present on the surface of the
target 4. The shutter plate 5 was then opened and thus film
deposition onto the side wall of the cylindrical or columnar
substrate was begun. The film deposition was performed for a
predetermined time period. After the completion of the film
deposition, the discharging of the target 4, the supplying of Ar
gas, and the heating of the substrate by means of the heater were
all stopped simultaneously. While evacuating the inside of the
vacuum chamber 1, the substrate remaining in the vacuum chamber 1
was cooled at a slow cooling rate. Thus, an Nd-Fe-B thin film in a
cylindrical form was obtained.
Table 8 shows designed and measured dimensions of the cylindrical
Nd--Fe--B ferromagnetic thin films. As can be seen from Table 8,
the obtained films deviated on the order of only 1 .mu.m from an
ideal circular shape and also have high dimensional accuracy of a
similar order. The thickness of the magnet can be controlled with
an accuracy of .+-.0.05 .mu.m. Therefore, it is possible to achieve
even smaller deviations from an ideal circular shape on the order
of submicrons.
TABLE 8 ______________________________________ DESIGNED MEASURED
VALUE VALUE SAMPLE PARAMETER (.mu.m) (.mu.m)
______________________________________ 1 OUTER DIAMETER 3010.0
3009.1-3011.2 DEVIATION FROM 0 1.6 IDEAL CIRCLE THICKNESS 10.0
9.95-10.05 2 OUTER DIAMETER 910.0 909.0-9011.3 DEVIATION FROM 0 1.7
IDEAL CIRCLE THICKNESS 10.0 9.95-10.05
______________________________________
The radial anisotropy of the Nd--Fe--B ferromagnetic thin films in
cylindrical form was evaluated by means of X-ray diffusion
analysis. Ten positions were marked at equal intervals along the
circumference at the center of the cylindrical ferromagnetic thin
film in the longitudinal direction. Each of these ten marked
positions was illuminated with an X-ray beam having a diameter of
10 .mu.m, so that X-ray diffraction patterns were obtained.
FIG. 19 illustrates a typical X-ray diffraction pattern. From FIG.
19, it can be seen that the C-axis of the Nd.sub.2 Fe.sub.14 B
crystal is oriented in the direction across the film thickness.
This means that the obtained film is a perpendicular magnetization
film. All marked points showed similar diffraction patterns, which
means that the obtained cylindrical film has radially anisotropic
magnetic properties. Thus, in this example, a cylindrical magnetic
thin film with radial anisotropy having a size on the order of a
millimeter or submillimeter was obtained.
EXAMPLE 8
In this example, the film deposition apparatus shown in FIG. 14 was
employed, and a sintered alloy of Nd--Fe--B, a Co--Cr alloy, a Ba
ferrite, or (Nd, Tb)--Fe--B was used as the target 4. According to
a procedure similar to that in Example 7, cylindrical ferromagnetic
thin films having a thickness of about 1 .mu.m were deposited on
the side wall of cylindrical or columnar substrates made of various
materials with an outer diameter of 3 mm and a length of 30 mm
wherein the deposition was performed at a substrate temperature of
560.degree. C. and at an Ar gas pressure of 1 Pa for all samples
except for the Co-Cr alloy in which the substrate temperature was
kept at 300.degree. C. Table 9 shows the results of the radial
anisotropy of the cylindrical ferromagnetic thin films obtained.
The radial anisotropy was evaluated on the basis of the X-ray
diffraction patters obtained in a manner similar to Example 7. That
is, ten positions on each cylindrical film were marked, and X-ray
diffraction measurement was performed at each of these points. The
total peak density .SIGMA.I relating to the ferromagnetic compounds
forming the main phase of each film and the peak intensity
I.sub.(00m) (m: integer in the range of from 1 to 10) relating to
the C-plane were determined. The ratios .SIGMA.I.sub.(00m)
/.SIGMA.I were calculated. The averaged value for each sample is
shown in Table 9.
TABLE 9 ______________________________________ RADIAL SAMPLE FILM
MATERIAL SUBSTRATE.sup.a ANISOTROPY
______________________________________ 1 Nd--Fe--B quartz glass
0.93 2 Nd--Fe--B quartz glass(*) 0.93 3 Nd--Fe--B Al.sub.2 O.sub.3
0.92 4 Nd--Fe--B Fe 0.89 5 Nd--Fe--B Fe--Ni 0.88 6 Nd--Fe--B Fe--Co
0.91 7 Nd--Fe--B TiN 0.90 8 Co--Cr quartz glass 0.93 9 Ba ferrite
quartz glass 0.89 10 (Nd, Tb)--Fe--B quartz glass 0.93 11 (Nd,
Tb)--Fe--B Fe--Ni 0.90 12 (Nd, Tb)--Fe--B TiN 0.92
______________________________________ .sup.a : The Substrate
marked with (*) is a cylindrical substrate and others are columnar
substrate.
As can be seen from Table 9, all the Nd-Fe-B thin films deposited
on any type of columnar substrate showed high radial anisotropy
greater than 0.88. This means that a variety of materials such as
glass, metal, alloys, oxides, and nitrides can be employed as the
substrate. The Co--Cr and Ba ferrite thin films also showed high
radial anisotropy. This apparently means that not only rare earth
element-transition metal based alloys such as Nd--Fe--B, but also
vertical magnetic recording materials such as Co--Cr alloys, and Ba
ferrites, and magneto-optic recording materials may also be
employed as the thin film material. In particular, as can be seen
from Table 9 and Tables 5 and 6 described above, if (Nd, R)--M--B
alloys according to the present invention are used, it is possible
to obtain a cylindrical thin film magnet having high radial
anisotropy and also having a high maximum energy product.
EXAMPLE 9
In this example, the film deposition apparatus shown in FIG. 14 was
employed. Using a SiO.sub.2 target 4, a SiO.sub.2 buffer layer
having a thickness of about 0.5 .mu.m was deposited on the side
wall of a Cu columnar substrate according to a procedure similar to
that in Example 7, wherein deposition was performed at a substrate
temperature of 100.degree. C. and at an Ar gas pressure of 2 Pa.
After completing the deposition of the SiO.sub.2 buffer layer, the
target was switched to a sintered Nd--Fe--B alloy, and an Nd--Fe--B
cylindrical thin film having a thickness of about 2 .mu.m was
deposited on the SiO.sub.2 buffer layer at a substrate temperature
of 560.degree. C. and at an Ar gas pressure of 4 Pa. Table 10 shows
the adhesion between the substrate and the Nd--Fe--B cylindrical
thin film. For comparison, adhesion for a sample in which a
Nd--Fe--B thin film was directly deposited on a Cu columnar
substrate without a buffer layer is also shown in Table 10.
Adhesion was evaluated by means of a tape peeling test. That is,
after sticking tape to the Nd--Fe--B cylindrical thin films, the
tape was removed at a constant speed and at a constant angle, and
adhesion was evaluated by judging whether the cylindrical thin
films peeled off the substrates.
TABLE 10 ______________________________________ SUBSTRATE BUFFER
ADHESION (TAPE SAMPLE MATERIAL LAYER PEELING TEST)
______________________________________ THIS EMBODIMENT Cu SiO.sub.2
no peeling COMPARATIVE Cu none almost entire film SAMPLE peeled off
______________________________________
As can be seen from Table 10, the comparative sample was poor in
adhesion and thus almost the whole cylindrical thin film peeled
off. In contrast, the sample according to the invention shows no
peeling of the cylindrical thin film since the buffer layer
enhances adhesion between the thin film and the substrate.
EXAMPLE 10
Deposition was performed using the film deposition apparatus shown
in FIG. 14 with a Ti or Zr metal target 4. According to a procedure
similar to that in Example 7, a Ti or Zr buffer layer having a
thickness of about 0.5 .mu.m was deposited on a quartz or Fe
columnar substrate wherein the deposition was performed at a
substrate temperature of 200.degree. C. and at an Ar gas pressure
of 2 Pa. After completing the deposition of the buffer layer, the
target was switched to a Co--Cr alloy, and a Co--Cr cylindrical
thin film having a thickness of about 1 .mu.m was deposited on the
buffer layer at a substrate temperature of 300.degree. C. and at an
Ar gas pressure of 5 Pa. The remits are shown in Table 11 not only
for samples having a buffer layer but also for comparative samples
having no buffer layer.
TABLE 11 ______________________________________ SUBSTRATE BUFFER
RADIAL SAMPLE MATERIAL LAYER ANISOTROPY
______________________________________ 1 quartz glass Ti 0.99 2
quartz glass Zr 0.98 3 Fe Ti 0.99 COMP. 1 quartz glass none 0.93
COMP. 2 Fe none 0.92 ______________________________________
The results shown in Table 11 indicate that the buffer layer formed
on the columnar substrate leads to an improvement in the radial
anisotropy.
* * * * *