Indian Patents
Title of Invention

A PROCESS FOR PRODUCING A HEXAGONAL FERRITE SINTERED MAGNET
Abstract A process for producing a hexagonal ferrite sintered magnet comprises a primary phase of a hexagonal ferrite containing A, Co, R and Fe, where A represents Sr, Ba or Ca, and R represents at least one element selected from rare earth elements including Y, and Bi, said process comprising adding a part or whole of constituent elements to ferrite particles comprising a primary phase of a hexagonal ferrite containing Sr, Ba or Ca ; molding mixture and sintering the molded material.
Full Text FIELD OF THE INVENTION
The present invention relates to a process for producing a hexagonal
ferrite sintered magnet, and generally to a hexagonal ferrite suitably used as a
permanent magnet material such as a motor for an automobile, and particularly
relates to a magnet material containing a hexagonal magnetoplumbite ferrite,
and a process for producing the same.
BACKGROUND OF THE INVENTION
As an oxide permanent magnet material, a strontium
(Sr) ferrite and a barium (Ba) ferrite, which are of a
magnetoplumbite (M type) hexagonal structure, are mainly
used, and they are produced as a sintered magnet and a
bonded magnet.
What are important among characteristics of a magnet
are a residual magnetic flux density (Br) and an intrinsic
coercive force (HcJ).
Br is determined by the density of the magnet, the
degree of orientation of the magnet, and the saturation
magnetization (4ls) determined by the crystal structure.
Br is expressed by the following equation:
Br = 4ΠIS x (degree of orientation) x (density)

The Sr ferrite and the Ba ferrite of M type has a 4ΠIS
value of about 4.65 kG. The density and the degree of
orientation each is about 98% at most in the sintered
magnet, which provides the highest values. Therefore, Br
of these magnets is limited to about 4.46 kG at most, and
it has been substantially impossible to provide a high Br
value of 4.5 kG or more.
The inventor of the invention have found that the
addition of appropriate amounts of La and Zn in an M type
ferrite raises its 4ΠIS value by about 200 G at most, and a
Br value of 4.5 kG or more can be obtained, as described in
US Patent Application Serial No. 08/672,848. In this case,
however, since the anisotropic magnetic field (HA) , which
will be described later, is decreased, it is difficult to
obtain a Br value of 4.5 kG or more and an HcJ of 3.5 kOe
or more at the same time.
HeJ is in proportion to the product (HA x fc) of the
anisotropic magnetic field (HA = 2K1/Is) and a single
magnetic domain grain fraction (fc), in which K1 represents
a crystal magnetic anisotropy constant, which is determined
by the crystal structure as similar to Is. The M type Ba
ferrite has K1 of 3.3 x 106 erg/cm3, and the M type Sr
ferrite has K1 of 3.5 x 106 erg/cm3. It has been known that
the M type Sr ferrite has the largest K1. value, but it has

been difficult to further raise the K1 value.
On the other hand, in the case where ferrite
particles are in a single magnetic domain condition, the
maximum HcJ is expected because the magnetization must be
rotated against the anisotropic magnetic field to reverse
the magnetization. In order to make ferrite particles into
single magnetic domain particles, the size of the ferrite
particles must be smaller than the following critical
diameter (dc) expressed by the following equation:
dc = 2(k.Tc.k/a)1/2/Is2
wherein k represents the Boltzman constant, Tc represents a
Curie temperature, and a represents a distance between iron
ions. In the case of the M type Sr ferrite, since dc is
about 1 µm, it is necessary for producing a sintered magnet
that the crystal grain size of the sintered magnet must be
controlled to 1 µm or less. While it has been difficult to
realize such a fine crystal grain and the high density and
the high degree of orientation to provide a high Br at the
same time, the inventor has proposed a new production
process to demonstrate that superior characteristics that
cannot be found in the art are obtained, as described in US
Patent Application Serial No. 08/072,967. In this process,
however, the HcJ value becomes 4.0 kOe when the Br value is

4.4 kG, and therefore it has been difficult to obtain a
high HeJ of 4.5 kOe or more with maintaining a high Br of
4.4 kG or more at the same time.
In order to control a crystal grain size of a
sintered body to 1 nm or less, it is necessary to make the
powder size in the molding step 0.5 µm or less with taking
the growth of the grains in the sintering step into
consideration. The use of such fine particles brings about
a problem in that the productivity is generally
deteriorated due to increase in molding time and increase
in generation of cracks on molding. Thus, it has been very
difficult to realize high characteristics and high
productivity at the same time.
It has been known that the addition of A12O3 and Cr2O3
is effective to obtain a high HcJ value. In this case, Al3+
and Cr3+ have effects of increasing HA and suppressing the
grain growth by substituting for Fe3+ having an upward spin
in the M type structure, so that a high HcJ value of 4.5
kOe or more is obtained. However, when the Is value is
reduced, the Br value is considerably reduced since the
sintered density is reduced. As a result, the composition
exhibiting the maximum HeJ of 4.5 kOe can only provide a Br
value of 4.2 kG.
A sintered magnet of the conventional anisotropic M
type ferrite has a temperature dependency of HcJ of about

+13 Oe/°C and a relatively high temperature coefficient of
about from +0.3 to +0.5%/°C, which sometimes bring about
great reduction in HcJ on the low temperature side and thus
demagnetization. In order to prevent such demagnetization,
the HcJ value at room temperature must be a large value of
about 5 kOe, and therefore it is substantially impossible
to obtain a high Br value at the same time. Powder of an
isotropic M type ferrite has a temperature dependency of
HcJ of at least about +8 Oe/°C, although it is superior to
the anisotropic sintered magnet, and a temperature
coefficient of +0.15%/°C. and thus it has been difficult to
further improve the temperature characteristics. Because a
ferrite magnet is excellent in environmental resistance and
is not expensive, it is frequently used in a motor in
various parts of an automobile. Because an automobile may
be used under severe conditions including intense cold and
heat, the motor is required to stably function under such
severe conditions. However, the conventional ferrite
magnet has a problem of considerable deterioration in
coercive force under low temperature conditions, as
described in the foregoing.
Even though a ferrite magnet satisfies such
characteristics, it has a problem in that those having a
low squareness (Hk/HcJ) in the demagnetization curve have a
low (BH)max and a deteriorated change with time.

If a magnet having a high degree of orientation,
which is obtained by the production process using an
organic solvent system, can be obtained by a production
process using an aqueous solvent, the production becomes
easy to provide advantages in productivity, and moreover it
does not lead environmental contamination to make possible
to omit apparatuses for preventing contamination.
SUMMARY OF THE INVENTION
An object of the invention is to provide a ferrite
magnet and a process for producing the same, which has a
high residual magnetic flux density and a high coercive
force that cannot be attained by the conventional M type
ferrite magnet, is excellent in temperature characteristics
of coercive force, has excellent magnetic characteristics
in that decrease in coercive force does not occur
particularly in a low temperature region, and is excellent
in squareness in the demagnetization curve.
Another object of the invention is to provide a
ferrite magnet and a process for producing the same, which
can exhibit superior characteristics even though the
content of expensive Co is reduced.
Further object of the invention is to provide a
ferrite magnet and a process for producing the same, which
exhibits a high degree of orientation that can be realized
by the organic solvent system even though it is produced by

a production process using an aqueous system.
Still further object of the invention is to provide a motor and a magnetic
recording medium having excellent characteristics.
Accordingly, the present invention provides a process for producing a
hexagonal ferrite sintered magnet comprising a primary phase of a hexagonal
ferrite containing A, Co, R and Fe, where A represents Sr, Ba or Ca, and R
represents at least one element selected from rare earth elements including
Y, and Bi, said process comprising adding a part or whole of constitutent
elements to ferrite particles comprising a primary phase of a hexagonal ferrite
containing Sr, Ba or Ca; molding mixture and sintering the molded material.
It is to be understood that rare earth elements referred to throughout
the description and claims do not include any radioactive substance.
The objects of the invention can be attained by one of the constitutions
(1) to (26) described below.
(1) Magnet powder comprising a primary phase of a hexagonal ferrite
containing Sr or Ba, Co and R, where R represents at least one element
selected from the group consisting of rate earth elements including Y, and Bi,
wherein the magnet powder has at least two different Curie temperatures, the
two different Curie temperatures are present within a range of from 400 to
470° C, and an absolute value of a difference therebetween is 5° C or more.

(2) Magnet powder as described in item (1), wherein
R represents at least La.
(3) Magnet powder as described in item (1) or (2).
wherein the hexagonal ferrite is a magnetoplumbite ferrite.
(4) Magnet powder as described in any one of items
(1) to (3), wherein the hexagonal ferrite comprises A, R,
Fe, and M,
wherein A represents at least one element selected
from the group consisting of Sr, Ba, Ca and Pb, provided
that Sr or Ba are essentially included in A,
R represents at least one element selected from the

group consisting of rare earth elements including Y, and Bi,
and
M represents Co, or Co and Zn,
and
proportions of the elements with respect to the total
amount of the metallic elements are
from 1 to 13 atomic% for A,
from 0.05 to 10 atomic% for R,
from 80 to 95 atomic% for Fe, and
from 0.1 to 5 atomic% for M.
(5) Magnet powder as described in any one of items
(1) to (4), wherein the proportion of Co in M is 10 atomic%
or more.
(6) Magnet powder as described in any one of items
(1) to (5), wherein the magnetic powder has an absolute
value of a temperature coefficient of a coercive force
within a range of from -50 to 50°C of 0.1%/°C or less.
(7) A bonded magnet comprising magnet powder as
described in any one of items (1) to (6).
(8) A motor comprising a bonded magnet as described
in item (7).
(9) A magnetic recording medium comprising magnet
powder as described in any one of items (1) to (6).
(10) A sintered magnet comprising a primary phase of
a hexagonal ferrite containing Sr or Ba, Co and R, where R

represents at least one element selected from the group
consisting of rare earth elements lincluding Y, and Bi,
wherein the sintered magnet has at least two
different Curie temperatures, the two different Curie
temperatures are present within a range of from 400 to 470°
C, and an absolute value of a difference therebetween is 5°
C or more.
(11) A sintered magnet as described in item (10),
wherein R represents at least La.
(12) A sintered magnet as described in item (10) or
(11), wherein the hexagonal ferrite is a magnetoplumbite
ferrite.
(13) A sintered magnet as described in any one of
items (10) to (12), wherein the hexagonal ferrite comprises
A, R, Fe, and M,
wherein A represents at least one element selected
from the group consisting of Sr, Ba, Ca and Pb, provided
that Sr or Ba are essentially included in A,
R represents at least one element selected from the
group consisting of rare earth elements including Y, and Bi,
and
M represents Co, or Co and Zn,
and
proportions of the elements with respect to the total
amount of the metallic elements are

from 1 to 13 atomic% for A,
from 0.05 to 10 atomic% for R,
from 80 to 95 atomic% for Fe, and
from 0.1 to 5 atomic% for M.
(14) A sintered magnet as described in any one of
items (10) to (13), wherein the proportion of Co in M is 10
atomic% or more.
(15) A sintered magnet as described in any one of
items (10) to (14), wherein the sintered magnet has a
squareness Hk/HcJ of 90% or more.
(16) A sintered magnet as described in any one of
items (10) to (15), wherein the sintered magnet has a
degree of orientation Ir/Is of 96% or more.
(17) A sintered magnet as described in any one of
items (10) to (15), wherein the sintered magnet a ratio of
a total X-ray diffraction intensity from c plane (2l(00L))
to a total X-ray diffraction intensity from all planes (2
I(hkL)) of 0.85 or more.
(18) A sintered magnet as described in any one of
items (10) to (17), wherein the sintered magnet has an
absolute value of a temperature coefficient of a coercive
force within a range of from -50 to 50°C of 0.25%/°C or
less.
(19) A motor comprising a sintered magnet as
described in any one of items (10) to (18).

(20) A magnetic recording medium comprising a thin
film magnetic layer comprising a primary phase of a
hexagonal ferrite containing Sr or Ba, Co and R, where R
represents at least one element selected from the group
consisting of rare earth elements including Y, and Bi,
wherein the thin film magnetic layer has at least two
different Curie temperatures, the two different Curie
temperatures are present within a range of from 400 to 470°
C, and an absolute value of a difference therebetween is 5°
C or more.
(21) A process for producing a hexagonal ferrite
sintered magnet comprising a primary phase of a hexagonal
ferrite containing A, Co, R and Fe, where A represents Sr,
Ba or Ca, and R represents at least one element selected
from rare earth elements including Y, and Bi,
said process comprising adding a part or whole of
the constitutional elements to ferrite particles comprising
a primary phase of a hexagonal ferrite containing Sr, Ba or
Ca; molding the mixture; and sintering the molded material.
(22) A process for producing a hexagonal ferrite
sintered magnet as described in item (21), wherein said
part of the constitutional elements is at least one element
selected from Co and R.
(23) A process for producing a hexagonal ferrite
sintered magnet as described in item (21) or (22), wherein

in adding a part or whole of the constitutional elements.
Si and Ca are further added.
(24) A process for producing a hexagonal ferrite
sintered magnet as described in any one of items (21) to
(23), wherein in adding a part or whole of the
constitutional elements, a dispersant is further added.
(25) A process for producing a hexagonal ferrite
sintered magnet as described in any one of items (21) to
(24), wherein said part or whole of the constitutional
elements is added at pulverization.
(26) A process for producing a hexagonal ferrite
sintered magnet as described in item (24) or (25), wherein
said dispersant is an organic compound having a
hydroxyl group and a carboxyl group or a neutralized salt
thereof or a lactone thereof, an organic compound having a
hydroxy-methylcarbonyl group, or an organic compound having
an enol-type hydroxyl group capable of being dissociated as
an acid or a neutralized salt thereof; and
said organic compound has from 3 to 20 carbon atoms,
where a hydroxyl group is bonded to at least 50% of carbon
atoms other than carbon atoms double-bonded to an oxygen
atom.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an SEM photograph of the structure of a
plane of the sintered magnet Sample No. 1 of the invention.

Figure 2 is an SEM photograph of the structure of c.
plane of the sintered magnet Sample No. 1 of the invention.
Figure 3 is an SEM photograph of the structure of a.
plane of the Comparative Sample No. 3.
Figure 4 is an SEM photograph of the structure of c
plane of the Comparative Sample No. 3.
Figure 5 is a graph showing a a-T curve of Sample No.
1 of the invention.
Figure 6 is a graph showing a a-T curve of Sample No.
2 of the invention.
Figure 7 is a graph showing a a-T curve of
Comparative Sample No. 1.
Figure 8 is a graph showing degrees of orientation
depending on the substituted amount of La and Co of the
samples of the invention.
Figure 9 is a graph showing HcJ-Br characteristics of
the samples of the invention.
Figure 10 is a graph showing degrees of orientation
of the samples of the invention.
Figure 11 is a graph showing degrees of magnetic
orientation of depending on the density at a calcination
temperature of 1,250°C.
Figure 12 is a graph showing HcJ-Br and Hk/HcJ at a
calcination temperature of 1,250°C.
Figure 13 is a graph showing squareness Hk/HcJ of the

sintered body samples at 1,220°C of the samples of the
invention.
Figure 14 is a graph showing degrees of magnetic
orientation (Ir/Is) depending on the substituted amount of
the samples of the invention.
Figure 15 is a graph showing magnetic characteristics
of the samples baked at 1,200°C, 1,220°C and 1,240°C.
Function and Effective
As a result of investigations with respect to
improvement in the magnetic characteristics made by the
inventors, it has been found that superior characteristics
is obtained by a magnetoplumbite ferrite, as described in
(Japanese Patent Application No. 9-56856). However, the
ferrite material having this composition only provides a
squareness of from 80 to 90% by the conventional production
process, where the addition is conducted at the mixing of
the raw materials. On the other hand, the inventors has
proposed a production process, in which a high degree of
orientation can be obtained by an aqueous process, as
described in US Patent Application Serial No. 08/984,087.
However, even when such a process is employed, it is not
sufficient as compared with a degree of orientation Ir/Is
of from 97 to 98% obtained by a process using an organic
solvent system proposed in US Patent Application Serial No.
08/072,967.

As a result of earnest investigations made by the
inventor taking these factors into consideration, it has
been found that a magnet having a high squareness can be
obtained by a magnetoplumbite ferrite having a structure
exhibiting two different Curie temperatures, as described
in Japanese Patent Application No. 9-56856 described above.
Furthermore, the employment of this structure can reduce
the content of Co.
It has been also found at the same time that as one
process for producing the structure, it is suitable to add
a compound containing at least one element selected from Sr
or Ba, R (where R represents rare earth elements including
Y), Co and Fe (i.e., oxides of these elements and compounds
that are converted into the oxides) on the step of
preparing a slurry for molding, preferably on the wet
pulverizing step or the dry pulverizing step. It has been
also found that by employing this production process, a
high degree of orientation that is obtained by the organic
solvent system can be obtained by using an aqueous
dispersant system.
A preferred composition of the M type Sr ferrite of
the invention is a composition containing at least optimum
amounts of La and Co. As a result, while Is is not lowered,
rather Is and K1. are simultaneously increased to increase
HA. and thus a high Br value and a hiqh HcJ value are

realized. Specifically, in the sintered magnet of the
invention, satisfactory characteristics can be obtained
when the coercive force HcJ (unit: kOe) and the residual
magnetic flux density Br (unit: kG) satisfy the following
conditions at an ordinary temperature of about 25°C:
When HcJ > 4
Br + 1/3HCJ > 5.75 (I)
When HcJ Br + 1/10HcJ > 4.82 (II)
It has been reported that the conventional Sr ferrite
sintered magnet exhibits Br of 4.4 kG and HcJ of 4.0 kOe,
but none has been obtained that has HcJ of 4 kOe or more
and satisfies the equation (I). In other words, if HcJ is
increased, Br must be low. In the sintered magnet of the
invention, although the combination addition of Co and Zn
lowers the coercive force lower than the case of the single
addition of Co, in some cases lower than 4 kOe, the
residual magnetic flux density is considerably increased.
At this time, the magnetic characteristics satisfying the
equation (II) are obtained. There has been no conventional
Sr ferrite sintered magnet having HcJ of less than 4 kOe
that satisfies the equation (II).

Because the ferrite of the invention has an
anisotropy constant Kx and an anisotropic magnetic field
(HA) larger than the conventional ferrite, a larger HcJ can
be obtained with the same grain size, and the grain size
can be reduced with the same HcJ to be obtained. For
example, an HcJ value of 4.5 kOe or more can be obtained
with an average grain diameter of the sintered body of from
0.3 to 1 µm, and even in the case of from 1 to 2 µm, an HcJ
value of 3.5 kOe or more can be obtained. Accordingly, the
time for pulverization and molding can be reduced, and the
improvement in yield of the product can be realized.
While the invention exhibits a greater effect of
enhancing the HcJ when applied to a sintered magnet,
ferrite powder produced according to the invention can be
mixed with a binder, such as plastics and rubber, to form a
bonded magnet.
Furthermore, a coating type magnetic recording medium
can be obtained in such a manner that a coating composition
is prepared by mixing and kneading the magnet powder with a
binder, and the coating composition is coated on a
substrate comprising a resin or the like, followed by
hardening if necessary, to form a magnetic layer.
The magnet material of the invention has a small
temperature dependency of HcJ, and particularly the magnet
powder of the invention has a considerably small

temperature dependency of HcJ. Specifically, the sintered
magnet of the invention has an absolute value of a
temperature coefficient of HcJ within a range of from -50
to 50°C of 0.25%/°C or less, which can be easily reduced to
0.20%/°C or less. The magnet powder of the invention has
an absolute value of a temperature coefficient of HcJ
within a range of from -50 to 50°C of 0.1%°C or less, which
can be easily reduced to 0.05%/°C or less. Owing to such
good temperature characteristics of HcJ, the excellent
magnetic characteristics satisfying the equation (V) can be
obtained. Such superior magnetic characteristics under the
low temperature environment cannot be attained by the
conventional Sr ferrite magnet.
A Ba ferrite represented by the following formula:
Ba1-xM3+xFe12-xM2+xOl9
is disclosed in Bull. Acad. Set. USSR, phys. Ser. (English
Transl.), vol. 25 (1961), pp. 1405-1408 (hereinafter
referred to as Reference 1). In this Ba ferrite, M3+ is
La3+, Pr3+ or Bi3+, and M2+ is Co2+ or Ni2+. While it is not
clear as to whether Ba ferrite of Reference 1 is powder or
a sintered body, this is similar to the Sr ferrite of the
invention in the point of inclusion of La and Co. Fig. 1
of Reference 1 shows the change of saturation magnetization

depending on the change of x for a Ba ferrite containing La
and Co, but in Fig. 1, the saturation magnetization is
reduced with the increase of x. Although Reference 1
discloses that the coercive force increases by a few times,
there is not disclosure of specific values.
In the invention, on the other hand, by employing the
composition, to which the optimum amounts of La and Co are
added, for the Sr ferrite magnet, the considerable increase
of HcJ and the slight increase of Br are realized, and the
considerable improvement in temperature dependency of HcJ
is also realized. In the invention, by adding the optimum
amounts of La and Co to the Sr ferrite magnet powder, the
HcJ is greatly increased and its temperature dependency is
considerably reduced. It is firstly found in the invention
that the combination addition of La and Co to a Sr ferrite
provides such effects.
A Ba ferrite represented by the following formula:
La3+Me2*Fe3+nO19
(Me2*: Cu2+ Cd2+ Zn2+, Ni2+ Co2+ or Mg2+)
is disclosed in Indian Journal of Pure and Applied Physics.
vol. 8, July 1970, pp.412-415 (hereinafter referred to as
Reference 2). This ferrite is similar to the magnet
material of the invention in the point of inclusion of La
and Co. However, in Reference 2, the saturation

magnetization as when M2+ is Co2+ is such low values of 42
cgs unit at room temperature and 50 cgs unit at OK. While
specific values are not disclosed, Reference 2 states that
it cannot be a magnet material due to a low coercive force.
It is considered this is because the composition of the
ferrite of Reference 2 deviates the scope of the invention
(the amounts of La and Co are larger than the invention).
An isometric hexagonal ferrite pigment represented by
the following formula:
Mx(I)My(II)Mz(III)Fe12-(y+z)O19
is disclosed in Japanese Patent Application Kokai No. 62-
100417 (hereinafter referred to as Reference 3). In the
formula, M(I) is a combination of Sr, Ba, a rare earth
metal, etc. with a monovalent cation; M(II) is Fe(II), Mn,
Co, Ni, Cu, Zn, Cd or Mg; and M(III) is Ti, etc. The
hexagonal ferrite pigment disclosed in Reference 3 is
similar to the magnet material of the invention in the
point that a rare earth metal and Co are simultaneously
contained. However, Reference 3 does not disclose any
example in that La and Co are simultaneously added, and
there is no disclosure that the simultaneous addition of
them improves the saturation magnetization and the coercive
force. Furthermore, in the examples of Reference 3 where

Co is added, Ti is simultaneously added as the element of
M(III). Because the element of M(III), particularly Ti.
functions as an element lowering the saturation
magnetization and the coercive force, it is clear that
Reference 3 does not suggest the constitution and the
effect of the invention.
An optomagnetic recording medium comprising a
magnetoplumbite barium ferrite characterized by
substituting a part of Ba with La and a part of Fe with Co
is disclosed in Japanese Patent Application Kokai No. 62-
119760 (hereinafter referred to as Reference 4). This Ba
ferrite is similar to the Sr ferrite of the invention in
the point of inclusion of La and Co. However, the ferrite
of Reference 4 is a material for "optomagnetic recording",
in which information is written as a magnetic domain in a
magnetic thin film by utilizing a heat effect of light, and
the information is read out by utilizing a optomagnetic
effect, which is of a technical field different from the
magnet material of the invention. Furthermore, in
Reference 4, Ba, La and Co are essential in the
compositional formula (I), and in the formulae (II) and
(III), there is only disclosed that an unidentified tetra-
valent metallic ion is added thereto. On the other hand,
the ferrite of the invention is the Sr ferrite, in which Sr
is essential, and the optimum amounts of La and Co are

added thereto, which is different from the composition of
Reference 4. That is, as explained with respect to
Reference 1, the Sr ferrite of the invention realizes the
considerable increase of HcJ and the slight increase of Br,
and also realizes the considerable improvement in
temperature dependency of HcJ, by using the composition of
the Sr ferrite magnet containing the optimum amounts of La
and Co. The effects can be obtained when the combination
addition of La and Co is applied to the Sr ferrite, and is
realized in the composition of the invention, which is
different from Reference 4.
DETAILED DESCRIPTION OF THE INVENTION
The magnet material of the invention comprising a
primary phase of a hexagonal magnetoplumbite ferrite
containing Sr or Ba, Co and R, where R represents at least
one element selected from the group consisting of rare
earth elements including Y, and Bi, wherein the magnet
material has at least two different Curie temperatures Tcl
and Tc2, the two different Curie temperatures are present
within a range of from 400 to 470°C, and an absolute value
of a difference therebetween is 5°C or more. Thus, the
magnet material has two different Curie temperatures,
whereby the squareness Hk/KcJ is markedly improved.
The Curie temperature can be obtained from an
inflection point of a magnetization a - temperature T curve

of a magnet. Specifically, it is obtained from the
temperature of the point of intersection of the tangent
line of the low temperature side curve at the inflection
point of the a-T curve and the temperature axis. The two
different Curie temperatures Tc1 and Tc2 exhibit the
absolute value of the difference therebetween of 5°C or
more, preferably 10°C or more. The upper limit thereof is
not particularly limited, but it is generally about 465°C.
These Curie temperatures fall within the range of from 400
to 470°C, preferably from 430 to 460°C. It is considered
that the two Curie temperature mean that the constructional
structure of the ferrite crystal of the invention has a
two-phase structure of an M type ferrite different in
magnetic properties due to the production process described
later, provided that a single phase of an M phase is
observed by ordinary X-ray diffractiometry.
The squareness Hk/HcJ is preferably 90% or more, more
preferably 92% or more, which becomes 95% at most. The
magnet of the invention preferably has a degree of
orientation Ir/Is of 96.5% or more, more preferably 97% or
more, which becomes about 98% at most. A high Br value can
be obtained by increasing the degree of orientation. Since
the degree of magnetic orientation of a molded body is
influenced by the density of the molded body, the
crystallographic degree of orientation (X-ray degree of

orientation) is important, which is obtained from the plane
index and the intensity of the peaks appearing in the X-ray
diffractiometry measurement result of the surface of the
molded body. The X-ray degree of orientation of the molded
body controls the degree of magnetic orientation of a
sintered body to a certain extent. Preferably, 2l(00L)/2
I(hkL) is used as the X-ray degree of orientation. (00L)
is an expression of the generic name of the c planes such
as (004) and (006), and ∑I(OOL) is a total intensity of the
peaks of all (00L) planes. (hkL) means all the peaks
detected, and 21(hkL) is a total intensity thereof. Thus,
ZI(OOL) /Zl(hkL) means the degree of c plane orientation. 2
I(00L)/2I(hkL) is preferably 0.85 or more, more preferably
0.9 or more, the upper limit of which is about 1.0. In the
following examples, this is expressed by 21(001)/2l(hkl) in
some cases.
The magnet of the invention comprises a primary phase
of a hexagonal magnetoplumbite ferrite containing Sr or Ba,
Co and R, where R represents at least one element selected
from the group consisting of rare earth elements /including
Y, and Bi, wherein the primary phase is preferably at least
one element selected from the group consisting of Sr, Ba,
Ca and Pb, and when A represents an element essentially
including Sr or Ba, R represents at least one element
selected from the group consisting of rare earth elements

including Y, and Bi, and M represents Co, or Co and Zn, the
proportions of the elements A, R, Fe and M with respect to
the total amount of the metallic elements are
from 1 to 13 atomic% for A,
from 0.05 to 10 atomic% for R,
from 80 to 95 atomic% for Fe, and
from 0.1 to 5 atomic% for M.
These are more preferably
from 3 to 11 atomic% for A,
from 0.2 to 6 atomic% for R,
from 83 to 94 atomic% for Fe, and
from 0.3 to 4 atomic% for M.
These are particularly preferably
from 3 to 9 atomic% for A,
from 0.5 to 4 atomic% for R,
from 86 to 93 atomic% for Fe, and
from 0.5 to 3 atomic% for M.
In the constitutional elements, A is at least one
element selected from the group consisting of Sr, Ba, Ca
and Pb. When the amount of A is too small, the M type
ferrite is not formed, or the amount of a non-magnetic
phase, such as -Fe2O3, is increased. When the amount of A
is too large, the M type ferrite is not formed, or the
amount of a non-magnetic phase, such as SrFeO3-x, is
increased. The proportion of Sr in A is preferably 51

atomic% or more, more preferably 70 atomlc% or more, and
especially preferably 100 atomic%. When the proportion of
Sr in A is too small, the improvement in saturation
magnetization and the considerable improvement in coercive
force is difficult to be obtained at the same time.
R is at least one element selected from the group
consisting of rare earth elements including Y, and Bi. It
is preferred that R essentially contains La, Nd and Pr,
particularly La. When the amount of R is too small, the
amount of M forming a solid solution becomes small, and
thus the effect of the invention is difficult to be
obtained. The amount of R is too large, the amount of a
non-magnetic foreign phase, such as ortho-ferrite, becomes
large. The proportion of La in R is preferably 40 atomic%
or more, more preferably 70 atomic% or more, and it is most
preferred to use only La as R from for the improvement in
saturation magnetization. This is because La exhibits the
largest limiting amount forming a solid solution with a
hexagonal M type ferrite. Therefore, when the proportion
of La in R is too small, the amount of R forming a solid
solution cannot become large, and as a result, the amount
of the element M forming a solid solution also cannot
become large, which reduces the effect of the invention.
The combination use of Bi lowers the calcination
temperature and the sintering temperature, and is

advantageous from the standpoint of productivity.
The element M is Co, or Co and Zn. When the amount
of M is too small, the effect of the invention is difficult
to be obtained. When the amount of M is too large, Br and HcJ are reduced, and the effect of the invention is
difficult to be obtained. The proportion of Co in M is
preferably 10 atomic% or more, more preferably 20 atomic%
or more. When the proportion of Co is too small, the
improvement in coercive force becomes insufficient.
The hexagonal magnetoplumbite ferrite is preferably
represented by the following formula:
A1-xRx(Fe12-yMy)zO19,
wherein
0.04 s x s 0.9, particularly 0.04 s; x s 0.6,
0.04 0.8s x/y s 5, and
0.7 s z s 1.2.
It is more preferably
0.04 s x 0.04 0.8 0.7 s z s 1.2.
It is particularly preferably

0.1 O.lsys 0.4, and
0.8 and especially preferably
0.9 In the above formula, when x is too small, i.e., the
amount of the element R is too small, the amount of the
element M forming a solid solution with the hexagonal
ferrite cannot be large, and thus the improving effect of
the saturation magnetization and/or the improving effect of
the anisotropic magnetic field become insufficient. When x
is too large, the element R cannot substitute in the
hexagonal ferrite to form a solid solution, and the
saturation magnetization is reduced due to the formation of
an ortho-ferrite containing the element R. When y is too
small, the improving effect of the saturation magnetization
and/or the improving effect of the anisotropic magnetic
filed becomes insufficient. When y is too large, the
element M is difficult to substitute in the hexagonal
ferrite to form a solid solution. Even in the range where
the element M can substitute to form a solid solution,
deterioration of the anisotropic constant (Kx) and the
anisotropic magnetic field (HA) becomes large. When z is
too small, the saturation magnetization is reduced since
the amounts of non-magnetic phases containing Sr and the

element R are increased. When z is too large, the
saturation magnetization is reduced since the amount of an
a-Fe2O3 phase or a non-magnetic spinel ferrite phase
containing the element M is increased. The above formula
assumes that no impurity is contained.
In the formula above, when x/y is either too small or
too large, the valences of the element R and the element M
cannot be balanced, and a foreign phase, such as a W type
ferrite, is liable to be formed. As the element M is
divalent, when the element R is trivalent, x/y is ideally 1.
The reason why the permissible range of x/y is largely
extended to the direction of more than 1 is that even if y
is small, the valences can be balanced by the reduction
from Fe3+ to Fe2+.
In the above formula showing the composition, the
number of oxygen atoms of 19 means the stoichiometric
compositional ratio when all the elements R are trivalent,
and x = y and z = 1. Thus, the number of oxygen atoms
changes depending on the kind of the element R and the
values of x, y and z. In the case where the sintering
atmosphere is a reducing atmosphere, there is a possibility
of forming lack of oxygen (vacancy). Furthermore, while Fe
is generally present as trivalent in the M type ferrite,
there is a possibility of changing it to divalent. There
is a possibility that the valence of the element

represented by M, such as Co, is changed, and the
proportion of oxygen to the metallic elements is also
changed according thereto. While the number of oxygen
atoms is shown as 19 irrespective to the kind of R and the
values of x, y and z in the specification, the actual
number of oxygen atoms may be somewhat deviated from the
stoichiometric compositional ratio.
The composition of a ferrite can be measured by
fluorescent X-ray quantitative analysis. The presence of
the primary phase described above is confirmed by X-ray
diffraction and electron beam diffraction.
The magnet powder may contain B2O3. The calcination
temperature and the sintering temperature can be lowered by
the addition of B2O3, which is advantageous from the
standpoint of productivity. The content of B2O3 is
preferably 0.5% by weight or less based on the total amount
of the magnet powder. When the content of B2O3 is too large,
the saturation magnetization becomes low.
At least one of Na, K and Rb may be contained in the
magnet powder. The total content of these elements, as
converted into Na20, K20 and Rb2O, is preferably 3% by
weight or less based on the total amount of the magnet
powder. When the content of these element is too large,
the saturation magnetization becomes low. As these
elements are represented by MI, MI are contained in the

ferrite in the form of the following formula:
Sr1.3-2aRaMIa-0.3Fe11.7M0.3O19
In this case, it is preferred that 0.3 is too large, the saturation magnetization becomes low, and
additionally a problem arises in that a large amount of the
element M1 is evaporated on sintering.
In addition to these impurities. Si, Al Ga, In, Li,
Mg, Mn, Ni, Cr, Cu, Ti, Zr, Ge, Sn, V, Nb. Ta, Sb, As, W
and Mo may be contained in the form of oxides in an amount
of 1% by weight or less for silicon oxide, 5% by weight or
less for aluminum oxide, 5% by weight or less for gallium
oxide, 3% by weight or less for indium oxide, 1% by weight
or less for lithium oxide, 3% by weight or less for
magnesium oxide, 3% by weight or less for manganese oxide,
3% by weight or less for nickel oxide, 5% by weight or less
chromium oxide, 3% by weight or less for copper oxide, 3%
by weight or less for titanium oxide, 3% by weight or less
for zirconium oxide, 3% by weight or less for germanium
oxide, 3% by weight or less for tin oxide, 3% by weight or
less for vanadium oxide, 3% by weight or less for niobium
oxide, 3% by weight or less for tantalum oxide, 3% by
weight or less for antimony oxide, 3% by weight or less for
arsenic oxide, 3% by weight or less for tungsten oxide, and

3% by weight or less for molybdenum oxide.
The process for producing the sintered magnet is
described below.
In the process for producing the sintered magnet
containing the above-described ferrite, iron oxide powder
and powder of compounds containing Fe, Sr or Ba, Co, R
(wherein R represents at least one element selected from
the group consisting of rare earth elements Including Y)
and Bi are used, and one kind of these raw material powder
or a mixture of two or more kinds thereof is calcined.
After calcination, one kind or two or more kinds of
compounds containing Fe, Sr, Co, R (wherein R represents at
least one element selected from the group consisting of
rare earth elements including Y) and Bi are added and mixed,
and then sintered. The powder of compounds containing Fe,
Sr, Co, R (wherein R represents at least one element
selected from the group consisting of rare earth elements
including Y) and Bi may be an oxide or a compound that is
converted into the oxide on heating, for example, a
carbonate, a hydroxide and nitrate. While the average
particle size of the raw material powder is not
particularly limited, iron oxide is preferably in a form of
fine powder, and more preferably has an average size of the
primary particle of 1 µm or less, especially preferably 0.5
µm or less. The raw material powder may further contain

depending on necessity, in addition to the above-described
components, B2O3 and other compounds, such as compounds
containing Si, Al, Ga, In, Li, Mg, Mn, Ni, Cr, Cu, Ti, Zr,
Ge, Sn, V, Nb, Ta, Sb, As, W and Mo, as well as unavoidable
impurities.
The calcination may be conducted in the air at a
temperature of from 1,000 to 1,350°C for from 1 second to
10 hours, particularly from 1 second to 3 hours.
The resulting calcined body substantially has a
magnetoplumbite ferrite structure, and the average particle
size of the primary particle is preferably 2 µm or less,
more preferably 1 pun or less, particularly preferably from
0.1 to 1 µm, especially preferably from 0.1 to 0.5 µm. The
average particle size can be measured by a scanning
electron microscope.
After pulverizing the calcined body, the sintered
magnet is produced by adding one kind or a mixture of two
or more kinds of compounds containing Fe, Sr or Ba, Co, R
(wherein R represents at least one element selected from
the group consisting of rare earth elements including Y)
and Bi, and molded, followed by sintering. Specifically,
it is preferably produced according to the following
procedures. The addition amount of the compound powder is
from 1 to 100% by volume of the calcined body, preferably
from 5 to 70% by volume, and particularly from 10 to 50% by

volume.
The time at which the compounds are added is not
particularly limited if it is after the calcining and
before the sintering, but it is preferred to add on
pulverizing described later. The kind and amount of the
raw material powder to be added are arbitrary, and the same
raw material may be added separately before and after the
calcination, provided that 30% or more, preferably 50% or
more of the total amount thereof is preferably added on a
step after the calcination. The average powder size of the
compound to be added is generally from 0.1 to 2 µm.
In the invention, wet molding is conducted by using a
slurry for molding containing oxide magnetic material
powder, water as a dispersing medium, and a dispersant. In
order to enhance the effect of the dispersant, a wet
pulverizing step is provided before the wet molding step.
In the case where the calcined material powder is used as
the oxide magnetic material powder, since the calcined
material powder is generally in a granule form, a dry
coarse pulverizing step is preferably provided before the
wet pulverizing step for coarse pulverization or
deflocculation of the calcined material powder. In the
case where the oxide magnetic material powder is produced
by a coprecipitation method or a hydrothermal synthesis
method, the dry coarse pulverizing step is generally not

provided, and the wet pulverizing step is not necessary,
but in order to further enhance the degree of orientation,
it is preferred to conduct the wet pulverizing step. In
the following, the case is described, in which the calcined
material powder is used as the oxide magnetic material
powder, and the dry coarse pulverizing step and the wet
pulverizing step are conducted.
In the dry coarse pulverizing step, pulverization is
conducted until the BET specific surface area becomes 2
times to 10 times the initial value. After pulverization,
the average particle diameter is preferably about from 0.1
to 1 µm, the BET specific surface area is preferably about
from 4 to 10m2/g, and the CV [Coefficient of Variation = Deviation/Expected
value] of the particle diameter is preferably maintained at 80% or less, more
preferably from 10 to 70%. This means for pulverization is not particularly
limited, and a dry vibration mill, a dry attritor (medium
stirring mill) and a dry ball mill can be used. It is
preferred to use a dry vibration mill. The pulverizing
time is appropriately determined depending on the
pulverizing means employed. It is preferred that a part of
the raw material powder is added on the dry pulverizing
step.
The dry coarse pulverization also has a function of
reducing the coercive force HcB by introducing crystal
distortion to the calcined material powder. Agglomeration

is suppressed by the reduction of the coercive force, and
the dispersibility is improved. The soft magnetization
improves the degree of orientation. The soft-magnetized
particles are restored into the inherent hard magnetization
through the subsequent sintering step to make a permanent
magnet.
On the dry pulverization, SiO2 and CaCO3 converted
into CaO on heating are generally added. A part of SiO2
and CaCO3 may be added before the calcination, and in that
case, improvement in characteristics is observed.
After the dry coarse pulverization, a slurry for
pulverization containing the pulverized powder and water is
prepared, and the wet pulverization is conducted using the
same. The content of the calcined material powder in the
slurry for pulverization is preferably about from 10 to 70%
by weight. The means for pulverizing used in the wet
pulverization is not particularly limited, a ball mill, an
attritor and a vibration mill are generally preferably used.
The pulverizing time is appropriately determined depending
on the pulverizing means employed.
After the wet pulverization, a slurry for molding is
prepared by condensing the slurry for pulverization. The
condensation can be conducted by centrifugation. The
content of the calcined material powder in the slurry for
molding is preferably about from 60 to 90% by weight.

In the wet molding step, molding is conducted in the
presence of a magnetic field by using the slurry for
molding. The pressure for molding can be about from 0.1 to
0.5 ton/cm2, and the applied magnetic field can be about
from 5 to 15 kOe.
The use of a non-aqueous dispersing medium in the
slurry for molding is preferred since a high degree of
orientation is obtained. In the invention, however, the
slurry for molding using an aqueous dispersing medium
containing a dispersant is employed. Examples of the
dispersant that is preferably used in the invention include
an organic compound having a hydroxyl group or a carboxyl
group, its neutralized salt, its lactone, an organic
compound having a hydroxymethylcarbonyl group, an organic
compound having an enol type hydroxyl group that can be
dissociated as an acid, and its neutralized salt.
In the case where a non-aqueous dispersing medium is
used, as described in e.g., US Patent Application Serial No.
08/072,967, a surface active agent, such as oleic acid, is
added to an organic solvent, such as toluene and xylene, to
form a dispersing medium. By using such a dispersing
medium, a high degree of magnetic orientation of 98% at the
highest even when ferrite grains of a submicron size, which
are hard to be dispersed, are employed.
The above-described organic compounds have a carbon

number of from 3 to 20, preferably from 4 to 12, in which
hydroxyl groups are bonded to 50% or more of the carbon
atoms except for the carbon atoms attached to oxygen atoms
via a double bond. When the carbon number is 2 or less,
the effect of the invention cannot be obtained. Even when
the carbon number is 3 or more, if the ratio of carbon
atoms, to which hydroxyl groups are attached, except for
the carbon atoms attached to oxygen atoms via a double bond
is less than 50%, the effect cannot be obtained. The ratio
of the carbon atoms, to which hydroxyl groups are attached,
is limited to the above-described organic compounds, and
there is no limitation for the dispersants themselves. For
example, when a lactone of an organic compound having a
hydroxyl group and a carboxyl group (hydroxycarboxylic
acid) is used as the dispersant, the ratio of the carbon
atoms, to which hydroxyl groups are attached, is applied to
the hydroxycarboxylic acid itself but not to the lactone.
The basic skeleton of the above-described organic
compounds may be a chainlike structure or a cyclic
structure, and may be saturated or may contain an
unsaturated bond.
A hydroxycarboxylic acid and its neutralized salt or
lactone are preferred as the dispersant. Particularly,
gluconic acid (C=6, OH=5, COOH=1) and its neutralized salt
or lactone, lactobionic acid (C=12, OH=8, COOH=1) and its

neutralized salt or lactone, tartaric acid (C=4. OH=2,
COOH=2) and its neutralized salt or lactone, and
glucoheptonic acid y-lactone (C=7, OH=5) are preferred.
Among these, gluconic acid and its neutralized salt or
lactone are particularly preferred since they provide a
high effect of improving the degree of orientation and are
not expensive.
Sorbose is preferred as the organic compound
containing a hydroxymethylcabonyl group.
Ascorbic acid is preferred as the organic compound
having an enol type hydroxyl group that can be dissociated
as an acid.
In the invention, citric acid and its neutralized
salt can be used as the dispersant. While citric acid has
a hydroxyl group and a carboxyl group, it does not satisfy
the condition in that hydroxyl groups are bonded to 50% or
more of the carbon atoms except for the carbon atoms
attached to oxygen atoms via a double bond. However,
citric acid provides an effect of improving the degree of
orientation.
The structures of a part of the preferred dispersants
described above are shown below.




The degree of orientation by the magnetic field
orientation is influenced by the pH of the supernatant
liquid of the slurry. Specifically, when the pH is too low.
the degree of orientation is decreased, and the residual
magnetic flux density after sintering is influenced
therefrom. In the case where a compound exhibiting an
acidic nature in an aqueous solution, such as
hydroxycarboxylic acid, is used as the dispersant, the pH
of the supernatant liquid of the slurry becomes low.
Therefore, it is preferred that the pH of the supernatant
liquid of the slurry is adjusted, for example, by adding a
basic compound along with the dispersant. As the basic
compound, ammonia and sodium hydroxide are preferred.
Ammonia may be added as aqueous ammonia. The lowering of
the pH can also be prevented by using a sodium salt of a
hydroxycarboxylic acid.
In the case where Si02 and CaC03 are added as
auxiliary components as in a ferrite magnet, when a

hydroxycarboxylic acid or its lactone is used as the
dispersant, SiO2 and CaCO3 effuse along with the
supernatant liquid of the slurry mainly on the preparation
of the slurry for molding, and the desired performance
cannot be obtained, for example. HcJ is decreased. When
the pH is heightened by adding the basic compound, the
effusing amount of SiO2 and CaCO3 becomes larger. On the
other hand, the use of a calcium salt of a
hydroxycarboxylic acid can suppress the effusion of SiO2
and CaCO3. By adding an excess amount of SiO2 and CaCO3 on
adding the basic compound or on using the sodium salt as
the dispersant, the shortage of the amounts of S102 and
CaCO3 in the magnet can be prevented. When the ascorbic
acid is used, there is substantially no effusion of SiO2
and CaCO3.
Because of the above-described reasons, the pH of the
supernatant liquid of the slurry is preferably 7 or more,
more preferably from 8 to 11.
The kind of the neutralized salt used as the
dispersant is not particularly limited, and may be any of a
calcium salt, a sodium salt, etc. Because of the above-
described reasons, a calcium salt is preferably used. When
a sodium salt is used as the dispersant, or aqueous ammonia
is added, a problem arises in that cracks are liable to be
formed in the molded body or the sintered body, in addition

to the effusion of the auxiliary components.
The dispersant may be used in combination of two or
more kinds thereof.
The addition amount of the dispersant is preferably
from 0.05 to 3.0% by weight, more preferably from 0.10 to
2.0% by weight, based on the calcined material powder as
the oxide magnetic material powder. When the amount of the
dispersant is too small, the improvement in degree of
orientation becomes insufficient. When the amount of the
dispersant is too large, cracks are liable to be formed in
the molded body and the sintered body.
In the case where the dispersant is one that can be
ionized in an aqueous solution, such as an acid or a
metallic salt, the addition amount of the dispersant is the
ion-converted value, i.e., the addition amount is obtained
by converting to only the organic component except for a
hydrogen ion and a metallic ion. In the case where the
dispersant is a hydrate, the addition amount is obtained
with excluding crystallization water. For example, when
the dispersant is calcium gluconate monohydrate, the
addition amount is obtained by converting into gluconic ion.
In the case where the dispersant is a lactone or
contains a lactone, the addition amount is obtained by
converting into a hydroxycarboxylic ion with assuming that
the whole lactone are split into a hydroxycarboxylic acid.

The time at which the dispersant is added is not
particularly limited. The dispersant may be added on the
dry coarse pulverizing step or the preparation of the
slurry for pulverization for the wet pulverizing step. A
part of the dispersant may be added on the dry coarse
pulverizing step and the balance may be added on the wet
pulverizing step. Alternatively, it may be added after the
wet pulverizing step with stirring. In any case, the
dispersant is present in the slurry for molding, and thus
the effect can be obtained. The addition on the
pulverizing step, particularly on the dry coarse
pulverizing step, provides higher effect of improving the
degree of orientation. It is considered that this is
because in the vibration mill used in the dry coarse
pulverization, a larger energy is applied to the particles,
and the temperature of the particle is increased, in
comparison to the ball mill used in the wet pulverization,
and thus the conditions in which chemical reactions are
liable to occur is realized. It is considered that by
adding the dispersant on the dry coarse pulverizing step,
the amount of the dispersant adsorbed on the surface of the
particles becomes larger, and consequently a higher degree
of orientation can be obtained. When the residual amount
of the dispersant in the slurry for molding (which is
substantially the same as the adsorbed amount) is actually

measured, the ratio of the residual amount to the addition
amount becomes higher in the case where the dispersant is
added on the dry coarse pulverizing step than the case
where the dispersant is added on the wet pulverizing step.
In the case where the addition of the dispersant is
conducted by separating to plural addition operations, the
addition amounts of each of the addition operations are
determined in such a manner that the total addition amount
is in the preferred range as described above.
After the molding step, the molded body is heat
treated in the air or nitrogen at a temperature of from 100
to 500°C to sufficiently remove the dispersant added. The
molded body is sintered in the subsequent sintering step,
for example, in the air at a temperature of from 1,150 to
1,250°C, preferably from 1,160 to 1,220°C, for about from
0.5 to 3 hours, to obtain an anisotropic ferrite magnet.
The average crystal grain diameter of the magnet of
the invention is preferably 2 µm or less, more preferably 1
µm or less, and especially preferably from 0.5 to 1.0 µm.
Even if the average crystal grain diameter exceeds 1 µm in
the invention, a sufficiently high coercive force can be
obtained. The crystal grain diameter can be measured with
a scanning electron microscope. The specific resistivity
is about 10o Ωm or more.
The sintered magnet can also be obtained in such a

manner that the molded body is pulverized by using a
crusher and classified to have the average grain diameter
of about from 100 to 700 nm by a sieve to obtain a magnetic
orientation granules, which is then subjected to a dry
molding in the presence of a magnetic field, and the
resulting molded body is sintered.
The magnet powder can be obtained in such a manner
that after the pulverization using the slurry of the
calcined material, the slurry is dried and sintered.
The invention involves a magnetic recording medium
comprising a thin film magnetic layer. The thin film
magnetic layer has a hexagonal magnetoplumbite ferrite
phase as similar to the magnet powder of the invention.
The content of impurities is equivalent to the above-
described embodiments.
The sputtering method is generally preferred for
providing the thin film magnetic layer. In the case where
the sputtering method is employed, the sintered magnet can
be used as a target, or a multi-sputtering method using at
least two kinds of targets may be employed. After the film
formation by the sputtering method, it is generally
subjected to a heat treatment to form the hexagonal
magnetoplumbite structure.
By using the magnet of the invention, the following
effects can generally obtained and superior application

products can be obtained. That is, in the case where the
magnet of the invention has the same dimension as the
conventional ferrite products, because the magnetic flux
density generated from the magnet can be increased, it
contributes to the provision of application products having
higher performance, for example, a high torque can be
obtained in the case of a motor, and a good sound quality
with high linearity can be obtained due to the
reinforcement of the magnetic circuit in the case of a
speaker or a headphone. In the case where the same
performance as the conventional magnet is enough, the size
(thickness) of the magnet can be small (thin), and it
contributes to make application products small-sized and
lightweight (thin). Furthermore, in the motor using a
wound type electromagnet as a magnet for a field system,
the electromagnet can be replaced by the ferrite magnet to
contribute to provision of the motor of lightweight and low
cost, and the reduction in production process thereof.
Furthermore, because the magnet of the invention is
excellent in temperature characteristics of the coercive
force (HcJ), it can be used under the low temperature
conditions, under which the conventional ferrite magnet
involves a danger of low temperature demagnetization
(permanent demagnetization), and thus the reliability of
products used in cold areas and areas highly above the sea

level can be considerably increased.
The magnet material of the invention is worked into
prescribed shapes and is used in the wide range of
applications described below.
The magnet material of the invention can be
preferably used as a motor for an automobile, such as for a
fuel pump, a power window, an antilock brake system, a fan,
a windshield wiper, a power steering, an active suspension
system, a starter, a door lock system and an electric side
mirror; a motor for an office automation and audio-visual
apparatus, such as for an Floppy Disk Drive (FDD) spindle, a Video Tape
Recorder (VTR) capstan, a VTR rotation head, a VTR reel, a VTR loading
system, a comcorder capstan, a camcorder rotation head, a camcorder
zooming system, a camcorder focusing system, a capstan for
a combination tape recorder and radio, a spindle for a
compact disk player, a laser disk player and a minidisk
player, a loading system for a compact disk player, a laser
disk player and a minidisk player, and an optical pickup
for a compact disk player and a laser disk player; a motor
for a home electric apparatus, such as for an air
compressor for a air conditioner, a compressor for a
refrigerator, driving an electric tool, an electric fan, a
fan for a microwave oven, a rotation system for a plate of
a microwave oven, driving a mixer, a fan for a hair dryer,
driving a shaver and an electric toothbrush; a motor for a

factory automation, such as for driving an axis and a joint
of an industrial robot, a main driver of an industrial
robot, driving a table of a working apparatus, and driving
a belt of a working apparatus; and a motor for other
applications, such as for a generator of a motor bike, a
magnet for a speaker and a headphone, a magnetron tube, a
magnetic field generator for an MRI system, a clamper for a
CD-ROM, a sensor of a distributor, a sensor of an antilock
brake system, a level sensor for a fuel and an oil, and a
magnet clutch.
EXAMPLE 1
Sintered magnet of Sample Nos. 1 and 2 were prepared
by using an aqueous system with the additive compounds
added after calcination.
As raw materials, the following materials were used.
Fe2O3 powder (primary particle size: 0.3 µm 1,000.0 g
(containing Mn. Cr, Si and C1 as impurities)
SrC03 powder (primary particle size: 2 µm) 161.2 g
(containing Ba and Ca as impurities)
As additives, the following materials were used.
SiO2 powder (primary particle size: 0.01 µm 2.30 g
CaCO3 powder (primary particle size: 1 µm) 1.72 g

The raw materials and the additives were pulverized
in a wet attritor, followed by drying and rectification of
granules, and baked in the air at 1,250°C for 3 hours, to
obtain a calcined material in the form of granules.
To the resulting calcined material, SiO2, CaCO3,
lanthanum carbonate (La2(CO3)3.8H2O) and cobalt oxide (CoO)
were added in the amounts shown in Table 1, and calcium
gluconate was further added in the amount shown in Table 1,
followed by dry coarse pulverization for 20 minutes by a
batch vibration rod mill. At this time, distortion due to
pulverization was introduced, and the HcJ of the calcined
material grains was lowered to 1.7 kOe.
Next. 177 g of the coarse pulverized material
produced in the same manner as above was collected, and
37.25 g of the same iron oxide (a-Fe2O3) was added thereto,
and 400 cc of water was further added thereto as a
dispersing medium, to prepare a slurry for pulverization.
By using the slurry for pulverization, wet
pulverization was conducted in a ball mill for 40 hours.
The specific surface area after the wet pulverization was
8.5 m2/g (average grain diameter: 0.5 µm . The pH of the
supernatant liquid of the slurry after the wet
pulverization was 9.5.
After the wet pulverization, the slurry for

pulverization was subjected to centrifugation to adjust the
concentration of the calcined material in the slurry to 78%,
so as to prepare a slurry for molding. Compression molding
was conducted by using the slurry for molding with removing
water from the slurry. The molding was conducted while
applying a magnetic field in the direction of compression
of about 13 kOe. The resulting molded body had a
cylindrical shape having a diameter of 30 mm and a height
of 18 mm. The molding pressure was 0.4 ton/cm2. A part of
the slurry was dried and fired at 1,000°C to convert the
whole contents thereof to oxides, and it was subjected to
the fluorescent X-ray quantitative analysis to obtain the
contents of the components. The results obtained are shown
in Tables 2 and 3.
The molded body was subjected to a heat treatment at
a temperature of from 100 to 300°C to sufficiently remove
gluconic acid, and then sintered in the air with a
temperature increasing rate of 5°C/min, followed by
maintained at 1,220°C for 1 hour, to obtain a sintered body.
The upper and lower surfaces of the resulting sintered body
were worked, and was measured for the residual magnetic
flux density (Br), the coercive force (HeJ and Hcb), the
maximum energy product ((BH)max), the saturation
magnetization (4ΠIS), the degree of magnetic orientation
(Ir/Is), and the squareness (Hk/HcJ). The sample was then

worked into a shape of 5 mm in diameter and 6.5 mm in
height. The Curie temperature Tc was obtained by measuring
the temperature dependency of the magnetization in the c
axis by VSM. The results obtained are shown in Figures 5
and 6. The SEM photographs of the structures in a. axis and
C axis of the samples are shown in Figures 1 and 2. It is
clear from Figures 5 and 6 that Sample Nos. 1 and 2 of the
invention each has two Curie temperatures of 440°C and 456°
C for Sample No. 1 and 434°C and 454°C for Sample No. 2. It
is considered therefrom that the crystal grains of the
samples of the invention have a two-phase structure in
which the phases have magnetic characteristics different
from each other. The samples were subjected to X-ray
diffractiometry, and as a result the samples were of a
monophase of an M type ferrite. No great difference in
lattice index therebetween.
COMPARATIVE EXAMPLE 1
Sintered magnet of Sample No. 3 was prepared by using
an aqueous system with the additive compounds added before
calcination.
As raw materials, the following materials were used.
Fe2O3 powder (primary particle size: 0.3 µm 1,000.0 g
(containing Mn, Cr, Si and C1 as impurities)
SrCO3 powder (primary particle size: 2 µm 130.3 g

(containing Ba and Ca as impurities)
Cobalt oxide 17.56 g
La2O3 35.67 g
As additives, the following materials were used.
SiO2 powder (primary particle size: 0.01 nm) 2.30 g
CaCO3 powder (primary particle size: 1 pun) 1.72 g
The raw materials and the additives were pulverized
in a wet attritor, followed by drying and rectification of
granules, and baked in the air at 1,250°C for 3 hours, to
obtain a calcined material in the form of granules. The
magnetic characteristics of the resulting calcined material
were measured with a vibration sample magnetomator (VSM),
and as a result, the saturation magnetization as was 68
emu/g and the coercive force HcJ was 4.6 kOe.
To the resulting calcined material, SiO2 and CaCO3
were added in the amounts shown in Table 1, and calcium
gluconate was further added in the amount shown in Table 1,
followed by dry coarse pulverization for 20 minutes by a
batch vibration rod mill. At this time, distortion due to
pulverization was Introduced, and the HcJ of the calcined
material grains was lowered to 1.7 kOe.
Next, 210 g of the coarse pulverized material thus-

produced was collected, and 400 cc of water was further
added thereto as a dispersing medium, to prepare a slurry
for pulverization.
By using the slurry for pulverization, wet
pulverization was conducted in a ball mill for 40 hours.
The specific surface area after the wet pulverization was
8.5 m2/g (average particle diameter: 0.5 µm) . The pH of
the supernatant liquid of the slurry after the wet
pulverization was from 9 to 10.
After the wet pulverization, the slurry for
pulverization was subjected to centrifugation to adjust the
concentration of the calcined material in the slurry to 78%,
so as to prepare a slurry for molding. Compression molding
was conducted by using the slurry for molding with removing
water from the slurry. The molding was conducted while
applying a magnetic field in the direction of compression
of about 13 kOe. The resulting molded body had a
cylindrical shape having a diameter of 30 mm and a height
of 18 mm. The molding pressure was 0.4 ton/cm2. A part of
the slurry was dried and fired at 1,000°C to convert the
whole contents thereof to oxides, and it was subjected to
the fluorescent X-ray quantitative analysis to obtain the
contents of the components. The results obtained are shown
in Tables 2 and 3.
The molded body was subjected to a heat treatment at

a temperature of from 100 to 360°C to sufficiently remove
gluconic acid, and then sintered in the air with a
temperature increasing rate of 5°C/min, followed by
maintained at 1.220°C for 1 hour, to obtain a sintered body.
The upper and lower surfaces of the resulting sintered body
were worked, and was measured for the residual magnetic
flux density (Br), the coercive force (HeJ and Hcb), the
maximum energy product ((BH)max), the saturation
magnetization (4ΠIS), the degree of magnetic orientation
(Ir/Is), and the squareness (Hk/HcJ). The results are
shown in Table 4. The sample was then worked into a shape
of 5 mm in diameter and 6.5 mm in height. The Curie
temperature Tc was obtained by measuring the temperature
dependency of the magnetization in the c axis by VSM. The
results obtained are shown in Figure 7. It is clear from
Figure 7 that the sample has one Curie temperature of 444°C.
The specific resistivity in the a axis direction and
the c axis direction of the sintered body samples Nos. 1 to
3 were measured. The results are shown in Table 5. The
SEM photographs of the structures observed from the a. axis
direction and the c. axis direction for the samples were
shown in Figures 3 and 4. It is clear from Figures 1 to 4
that the ferrite of the invention has a larger grain size
in comparison to the conventional ferrite shown in Figures
3 and 4.







It is clear from Table 4 that the cores of the
sintered bodies within the scope of the invention exhibited
extremely excellent characteristics.
It is clear from Table 5 that Sample Nos. 1 and 2 of
the invention obtained by the process of addition after the
calcination exhibited smaller specific resistivities of
1/10 to 1/100 of that of the comparative sample obtained by
the process of addition before the calcination. It is
considered therefrom that the sample obtained by the
process of addition before the calcination and the samples
obtained by the process of addition after the calcination
are different in fine structures of the sintered bodies.
Among the samples according to the invention. Sample No. 2
having the La-rich composition exhibited a smaller value of
1/4 to 1/2 of that of Sample No. 1. In all the samples,
the values of the a axis direction were smaller than the
values of the c axis direction.
EXAMPLE 2
A comparison was made for the addition of Fe, La and
Co after the calcination.
The composition as in Example 1 (SrFe12O19 + SiO2:
0.2% by weight + CaCO3: 0.15% by weight) was calcined in
the same manner as in Example 1, to obtain a calcined
material. To the resulting calcined material in the form
of granules, La2(CO3)3.8H20, CoOx(CoO+Co3O4) , the iron oxide

(-Fe2O3) and SiO2 (0.4% by weight), which were the same as
those used as the raw materials, CaCO3 (1.25% by weight),
and calcium gluconate (0.6% by weight) were added in such a
manner that the composition after the addition became the
following formula:
Sr1-xLaxFe12-xCoxO19
wherein x = y = 0, 0.1, 0.2 or 0.3, followed by subjecting
to the coarse pulverization using a small-sized vibration
mill. The composition was then subjected to the wet
pulverization in the same manner as in Example 1 for 40
hours, followed by baking. Separately, a sample wherein no
calcium gluconate was used but only water was used, and a
sample wherein xylene was used as the dispersing medium and
oleic acid was used as the dispersant were prepared.
The degrees of orientation of the molded bodies
depending on the addition amounts of La and Co for the
sintered body samples are shown in Figure 8, and the HcJ-Br
characteristics thereof are shown in Figure 9. The
addition amounts of Fe, La and Co after the calcination
were expressed by x, with the composition after the
addition being represented by the following formula:
Sr1-xLaxFe12-xCOx019

In the case where calcium gluconate was used as the aqueous
dlspersant, the clear increase in degree of orientation was
observed with the increase in the addition amount after the
calcination, and in the case of x (substitution degree) of
0.4, it was closed to the value obtained when xylene was
used as the non-aqueous solvent and oleic acid was used as
the surface active agent. On the other hand, no
improvement in degree of orientation was observed when no
gluconic acid was added to water. With respect to the
characteristics of the sintered bodies, in many cases,
Hk/Hcj > 90%, and it was the maximum that x = 0.2. When
the addition amount became large (x > 0.3), the moldability
was lowered.
EXAMPLE 3
A comparison was made for the addition of Fe before
the calcination, and La and Co after the calcination, and
was also made for the calcination temperatures.
To the composition as in Example 1 (SrFe12O19 + SiO2:
0.2% by weight + CaCO3: 0.15% by weight), the iron oxide (
-Fe2O3), which was the same as that used as the raw
material was added, in such a manner that the composition
was represented by the following formula:
Sr1-xLaxFe12-yCoyO19

wherein x = y = 0.2, and calcined materials were obtained
in the same manner as in Example 1 except that the
composition was calcined at 1,150°C, 1,200°C, 1,250°C and
1,300°C. The resulting calcined material samples were
subjected to X-ray diffraction analysis, and the presence
of the M phase and the hematite phase (α-Fe2O3) was
observed. The as value of the Sr M phase in the calcined
powder was then calculated under the assumption that in the
calcined material obtained by the process where Fe was
added before the calcination, the whole incremental amount
of Fe was converted into the α-Fe2O3 phase, and the balance
became the Sr M phase. As a result, it was substantially
equal to the as value of the Sr M calcined material at the
same calcination temperature, and therefore it was
considered that the assumption was reasonable.
To the resulting calcined material in the form of
granules, La2(CO3)38H2O, CoOx(CoO+Co3O4) + SiO2 (0.4% by
weight), CaCO3 (1.25% by weight), and calcium gluconate
(0.6% by weight) were added in such a manner that the
composition was represented by the following formula:
Sr1-xLaxFe12-yCOyO19
wherein x = y = 0.2, followed by subjecting to coarse

pulverization using a small-sized vibration mill. The
composition was then subjected to the wet pulverization in
the same manner as in Example 1 for 40 hours, followed by
baking.
The resulting molded body was measured for the degree
of orientation. The results obtained are shown in Figure
10. It is clear for Figure 10 that the degree of
orientation of molded body was high in the sample using the
calcined body at 1,250°C, which was equivalent to the
sample obtained by the process where all the additives were
added after the calcination. Figure 11 shows the
relationship between the sintered density and the degrees
of magnetic orientation (Ir/Is) at a calcination
temperature of 1,250°C. Although the degrees of
orientation of the molded body were the same, the sample
obtained by the process where only a-Fe203 was added before
the calcination had the higher density and the higher
degree of orientation. Figure 12 shows HcJ-Br and Hk/HcJ
at a calcination temperature of 1,250°C. In the sample
obtained by the process where only ct-Fe203 was added before
the calcination. HcJ was lowered but Br was high due to the
high density and degree of orientation, which was in the
same level of characteristics as the sample of Example 2.
EXAMPLE 4
A comparison was made for the addition of Fe and La

before the calcination, and only Co after the calcination.
To the composition as in Example 1 (SrFe12019 + SiO2:
0.2% by weight + CaCO3: 0.15% by weight), the iron oxide (a
-Fe2O3), which was the same as that used as the raw
material, and La2O3 were added in such a manner that the
composition was represented by the following formula:
Sr1-xLaxFe12-yCoyO19
wherein x = y = 0.2, and calcined materials were obtained
in the same manner as in Example 1 except that the
composition was calcined at 1,200°C or 1,250°C. The
resulting calcined material samples were subjected to X-ray
diffraction analysis, and the presence of the M phase and
the hematite phase (α-Fe2O3) was observed. A peak of ortho-
ferrite (FeLaO3) was not confirmed.
To the resulting calcined material in the form of
granules, CoOx(CoO+Co3O4) + SiO2 (0.4% by weight), CaCO3
(1.25% by weight), and calcium gluconate (0.6% by weight)
were added in such a manner that the composition was
represented by the following formula:
Sr1-xLaxFe12-yCOyO19
wherein x = y = 0.2, followed by subjecting to coarse

pulverization using a small-sized vibration mill. The
composition was then subjected to the wet pulverization in
the same manner as in Example 1 for 40 hours, followed by-
baking in the same manner as in Example 1.
Hcj-Br and Hk/HcJ are shown in Table 6.

EXAMPLE 5
A comparison was made for the addition of Fe and La
before the calcination, and only Co after the calcination.
To the composition as in Example 1 (SrFe12O19 + SiO2:
0.2% by weight + CaCO3: 0.15% by weight), La2(CO3). 8H2O was
added in such a manner that the composition after the
addition was represented by the following formula:
Sr1-xLaxFe12-yCOy019
wherein x = y = 0.1, 0.2, 0.3 or 0.4, to obtain calcined

powder (solvent system with addition before the
calcination). Separately, La2(CO3)3.8H2O was added after
the calcination in such a manner that the composition after
the addition was represented by the above formula wherein x
= y = 0, 0.1. 0.2, 0.3 or 0.4, to obtain calcined powder
(solvent system with addition after the calcination).
Oleic acid was added to these species of calcined powder,
followed by coarse pulverization by using a small-sized
vibration mill. The solvent pulverization was then
conducted for 40 hours, followed by baking, to obtain
samples.
The squareness Hk/HcJ of the resulting sintered body
sample obtained at 1,220°C is shown in Figure 13, and the
degree of magnetic orientation depending on the addition
amounts (Ir/Is) is shown in Figure 14. The degrees of
orientation of the samples were in the same level, and
Hk/HcJ of the sample of the addition after the calcination
was improved in comparison to the another.
EXAMPLE 6
Investigation was made for the separate addition of
La and Co.
As raw materials, the following materials were used.
Fe2O3 powder (primary grain size: 0.3 µm) 1,000.0 g
SrCO3 powder (primary grain size: 2 µm 161.2 g

These raw materials were pulverized in a wet attrltor,
followed by drying and rectification of granules, and baked
in the air at 1,250°C for 3 hours, to obtain a calcined
material in the form of granules.
To the resulting calcined material, SiO2 = 0.6% by
weight, CaCO3 = 1.4% by weight, lanthanum carbonate
(La2(CO3)3.8H20), cobalt oxide (CoO), and calcium gluconate
(0.9% by weight) were added on the pulverization by a dry
vibration mill. At this time, the La/Co ratio was changed
by changing the addition amount of La. Iron oxide (Fe203)
was added on the pulverization by a ball mill. Separately,
as the calcined material (referred to as mother material in
the Table), those of the addition amounts of lanthanum
carbonate (La2(CO3)3.8H2O) and cobalt oxide (CoO) before the
calcination x = 0 or 0.1 were prepared. The compositions
of the samples and the results of analysis of the
pulverized materials are shown in Table 7.



The resulting samples were baked at 1,200°C, 1,220°C
and 1,240°C, and measured for magnetic characteristics.
The results obtained are shown in Figure 15. In all the
samples, a relatively high HcJ and Hk values were obtained
in the case of the La-rich composition (La/Co = 1.14 to
1.23). As a comparison was made at the optimum point of
La/Co, in the case of the addition of x = 0.1 after the
calcination to the mother material of x = 0.1, Hk had a
tendency of deteriorated, and in the case of the addition
of x = 0.2 after the calcination to the mother material of
x = 0, high sintered magnetic characteristics were obtained.
It has been known that the addition of La and Co on
pulverization (after the calcination) provides a higher Hk
than the case of the addition to the raw material (before
the calcination). In this example, the intermediate
behavior was observed between these two cases, and no
characteristic result was obtained.
While the ferrites containing Sr have been considered
in the foregoing examples, it has been confirmed that the
equivalent results have been obtained for ferrites
containing Ba.
The shape of the samples of the invention obtained in
the foregoing examples was changed from the cylindrical
form to a shape of a filed magnet of a C type motor, to
produce a sintered magnet having a shape of a C type motor.

The resulting core materials were installed in a motor to
replace the sintered magnet of the conventional material.
The motor was operated at the rated conditions, and thus
good characteristics were exhibited. The torque of the
motor was observed, and thus the torque was increased in
comparison to the motor using the conventional core
material. The same results were obtained by using a bonded
magnet.
The effect of the invention is clear from the
foregoing examples.

WE CLAIM :
1. A process for producing a hexagonal ferrite sintered magnet
comprising a primary phase of a hexagonal ferrite containing A, Co, R and
Fe, where A represents Sr, Ba or Ca, and R represents^at least one
element selected from rare earth elements'including Y, and Bi,
said process comprising adding a part or whole of constituent
elements to ferrite particles comprising a primary phase of a hexagonal
ferrite containing Sr, Ba or Ca ; molding mixture and sintering the molded
material.
2. A process for producing a hexagonal ferrite sintered magnet as
claimed in claim 1, wherein said part of the constituent elements is at
least one element selected from Co and R.
3. A process for producing a hexagonal ferrite sintered magnet as
claimed in claim 1 or 2, wherein along with a part or whole of the
constituent elements, Si and Ca are further added.

4. A process for producing a hexagonal ferrite sintered magnet as
claimed in any one of claims 1 to 3, wherein a dispersant is added while
adding a part or whole of the constituent elements.
5. A process for producing a hexagonal ferrite sintered magnet as
claimed in any one of claims 1 to 4, wherein said part or whole of the
constituent elements is added during pulverization.

6. A process for producing a hexagonal ferrite sintered magnet as claimed in
claim 4 or 5, wherein said dispersant is :
an organic compound having a hydroxyl group and a carboxyl group or a
neutralized salt thereof or a lactone thereof;
an organic compound having a hydroxy-methylcarbonyl group ;
or
an organic compound having an enol-type hydroxyl group capable of
being dissociated as an acid or a neutralized salt thereof; and
said organic compound has 3 to 20 carbon atoms, a hydroxyl group being
bonded to at least 50% of carbon atoms other than carbon atoms double-
bonded to an oxygen atom.
7. A process for producing a hexagonal ferrite sintered magnet, substantially
as herein described, particularly with reference to the foregoing examples and
the accompanying drawings.

A process for producing a hexagonal ferrite sintered magnet comprises
a primary phase of a hexagonal ferrite containing A, Co, R and Fe,
where A represents Sr, Ba or Ca, and R represents at least one
element selected from rare earth elements including Y, and Bi, said
process comprising adding a part or whole of constituent elements to
ferrite particles comprising a primary phase of a hexagonal ferrite
containing Sr, Ba or Ca ; molding mixture and sintering the molded
material.

Documents:

1689-CAL-1998-FORM-27.pdf

1689-cal-1998-granted-abstract.pdf

1689-cal-1998-granted-claims.pdf

1689-cal-1998-granted-correspondence.pdf

1689-cal-1998-granted-description (complete).pdf

1689-cal-1998-granted-drawings.pdf

1689-cal-1998-granted-examination report.pdf

1689-cal-1998-granted-form 1.pdf

1689-cal-1998-granted-form 2.pdf

1689-cal-1998-granted-form 3.pdf

1689-cal-1998-granted-form 6.pdf

1689-cal-1998-granted-pa.pdf

1689-cal-1998-granted-priority document.pdf

1689-cal-1998-granted-reply to examination report.pdf

1689-cal-1998-granted-specification.pdf

1689-cal-1998-granted-translated copy of priority document.pdf


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Patent Number 229499
Indian Patent Application Number 1689/CAL/1998
PG Journal Number 08/2009
Publication Date 20-Feb-2009
Grant Date 18-Feb-2009
Date of Filing 21-Sep-1998
Name of Patentee TDK CORPORATION
Applicant Address 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
Inventors:
# Inventor's Name Inventor's Address
1 HITOSHI TAGUCHI C/O. TDK CORPORATION, 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
2 KIYOYUKI MASUZAWA C/O. TDK CORPORATION, 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
3 YOSHIHIKO MINACHI C/O. TDK CORPORATION, 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
4 KAZUMASA IIDA C/O. TDK CORPORATION, 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
5 FUMIHIKO HIRATA C/O. TDK CORPORATION, 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
6 MITSUAKI SASAKI C/O. TDK CORPORATION, 13-1, NIHONBASHI 1-CHOME, CHUO-KU, TOKYO
PCT International Classification Number H01F 1/11
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 9-273936 1997-09-19 Japan