Permanent magnet

Details Permanent magnet Permanent magnet

2000-12-28

2002-11-05

Sheehan, John (Department: 1742)

Metal treatment

Stock

Magnetic

C148S301000

Reexamination Certificate

active

06475302

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a permanent magnet, particularly, to a permanent magnet excellent in saturation magnetization and coercive force and having improved temperature characteristics of the coercive force.
A Sm—Co magnet, a Nd—Fe—B magnet, etc. are known as a high performance permanent magnet. These conventional permanent magnets are widely used in various motors such as VCM and a spindle motor, a measuring instrument, a loud speaker, MRI for medical treatment, and in key parts in various electrical appliances.
Each of these conventional permanent magnets contains a large amount of Fe or Co and a small amount of a rare earth element. Fe or Co contributes to the increase in the saturation magnetic flux density. On the other hand, the rare earth element brings about a very large magnetic anisotropy derived from the behavior of 4 f electrons in the crystalline field so as to contribute to the increase in the coercive force and, thus, realize good magnetic characteristics.
In recent years, demands for miniaturization of various electrical appliances and for energy saving are on a sharp increase. In this connection, further improvement in the maximum energy product [(BH)max] and in the temperature characteristics are required for the permanent magnet used as a material of a key part of these electrical appliances.
Under the circumstances, new magnet materials are being studied from various angles. For example, Japanese Patent Disclosure (Kokai) No. 60-144909 and Japanese Patent Disclosure No. 60-254707 disclose a permanent magnet represented by a general formula R
1−&agr;−&bgr;−&ggr;
Fe
&agr;
M
&bgr;
X
&ggr;
, where R is at least one rare earth element (including Y); M is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W; X is at least one element selected from the group consisting of B, C, N, Si and P; and &agr;, &bgr;, &ggr; fall within the ranges of: 0.6≦&agr;≦0.85; 0.01≦&bgr;≦0.1; &ggr;<0.15; and a method of manufacturing the particular permanent magnet.
On the other hand, Japanese Patent Disclosure No. 64-67902 and Japanese Patent Disclosure No. 5-226123 propose a magnetic material having a ThMn12 type crystal structure represented by R-Ti-Fe (R representing a rare earth element) and R1-R2-Si-M-T (R1 representing Zr or Hf; R2 representing a rare earth element; M representing C, N or P; and T representing Fe or Co).
Further, a magnetic material prepared by introducing N or C into an intermetallic compound based on Sm
2
Fe
17
exhibits an elevated Curie temperature and an improved magnetic anisotropy and, thus, attracts attentions as a novel magnetic material. However, this magnetic material leaves room for further improvement in the thermal stability. Specifically, this magnetic material is decomposed into a rare earth nitride or carbide and Fe at temperatures around 500° C., making it difficult to realize a sintered magnet. Also, further improvement in the magnetic characteristics is required. Particularly required are a high saturation magnetization and a high coercive force.
As described above, it is of high importance to develop a permanent magnet exhibiting a higher coercive force and a higher saturation magnetization (higher residual magnetization) in accordance with miniaturization and high efficiency of the electrical appliance and electronic equipment. Particularly, it is required to achieve a high coercive force and a high saturation magnetization (high residual magnetization) under the environmental temperature of using such an electrical appliance and electronic equipment.
It should be noted that an NbFeB magnet is poor in the temperature characteristics of the coercive force and, thus, the temperature range within which the magnet is used is limited. On the other hand, the sintered magnetic material or sintered magnet disclosed in, for example, Japanese Patent Disclosure No. 60-144906, which certainly exhibits a high coercive force of about 10 kOe, exhibits a relatively low residual magnetic flux density of about 12 kG and, thus, fails to exhibit sufficient characteristics of a magnet.
The SmFe alloy system in which TbCu7 phase can be obtained remains to be no more than utilization of what is obtained by the method of creating a so-called “non-equilibrium phase” such as the liquid rapid cooling method or the mechanical alloying method. Therefore, where an element such as N or C is introduced into the position between lattices, the thermal stability was not sufficient, though it may be possible to obtain relatively excellent magnetic characteristics.
On the other hand, the magnetic material having a ThMn12 type crystal structure, which is known to the art, includes materials of three element system such as SmFe
10
Si
2
, SmFe
10
Mo
2
, SmFe
10
V
2
, SmFe
10
Cr
2
, SmFe
10
W
2
and SmFe
11
Ti
1
. Each of these materials has a small coercive force and has not yet been put to a practical use as a permanent magnet.
In the alloy systems described above, a nonmagnetic element is substituted in a large amount in order to stabilize the ThMn12 phase, leading to a low saturation magnetization. Also, since a microstructure of (ferromagnetic phase+nonmagnetic phase) as in the NbFeB magnet is not formed, a sufficient coercive force is not obtained.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a permanent magnet excellent in saturation magnetization and coercive force and having improved temperature characteristics of the coercive force.
According to a first aspect of the present invention, there is provided a permanent magnet which comprises an alloy containing a hard magnetic phase having a ThMn12 type tetragonal structure and a nonmagnetic phase.
According to a second aspect of the present invention, there is provided a permanent magnet which comprises an alloy containing a hard magnetic phase having a ThMn12 type tetragonal structure and a nonmagnetic phase, wherein the alloy is represented by a general formula given below:
[R
1-a
(M1)
a
][T
1-b-c
(M2)
b
(M3)
c
]
d
x
&agr;
where R is at least one rare earth element (including Y); M1 is at least one element selected from the group consisting of Zr and Hf; T is at least one element selected from the group consisting of Fe, Co and Ni; M2 is at least one element selected from the group consisting of Cu, Bi, Sn, Mg, In and Pb; M3 is at least one element selected from the group consisting of Al, Ga, Ge, Zn, B, P and S; X is at least one element selected from the group consisting of Si, Ti, V, Cr, Mn, Nb, Mo, Ta and W; and the atomic ratios of a, b, c, d and &agr; fall within the ranges of: 0≦a≦0.6; 0.01≦b≦0.20; 0≦c≦0.05; 6≦d≦11; and 0.5≦&agr;≦2.0.
According to a third aspect of the present invention, there is provided a permanent magnet which comprises an alloy containing a hard magnetic phase having a ThMn12 type tetragonal structure and a nonmagnetic phase, wherein the alloy is represented by a general formula given below:
[R
1-a
(M1)
a
][T
1-b-c
(M2)
b
(M3)
c
]
d
x
&agr;
A
&bgr;
where R is at least one rare earth element (including Y); M1 is at least one element selected from the group consisting of Zr and Hf; T is at least one element selected from the group consisting of Fe, Co and Ni; M2 is at least one element selected from the group consisting of Cu, Bi, Sn, Mg, In and Pb; M3 is at least one element selected from the group consisting of Al, Ga, Ge, Zn, B, P and S; X is at least one element selected from the group consisting of Si, Ti, V, Cr, Mn, Nb, Mo, Ta and W; A is at least one element selected from the group consisting of N, C and H; and the atomic ratios of a, b, c, d and &agr; fall within the ranges of: 0≦a≦0.6; 0.01≦b≦0.20; 0≦c≦0.05; 6≦d≦11; 0.5≦&agr;≦2.0; and 0<&bgr;<≦2.0.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by

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