Rare earth based magnet
The present invention provides a rare earth based magnet in which the demagnetization rate at a high temperature can be inhibited even if the amount of heavy rare earth element(s) such as Dy and Tb is evidently decreased compared to the past or no such heavy rare earth element is used. The rare earth based magnet of the present invention is a sintered magnet which comprises R 2 T 14 B crystal grains as the major phases and the crystal boundary phases among the R 2 T 14 B crystal grains. The microstructure of the sintered body is controlled by including crystal boundary phases containing at least R, T and M in the crystal boundary phases, wherein the relative atomic ratios of R, T and M are as follows, i.e., 60 to 80% for R, 15 to 35% for T and 1 to 20% for M.
1. A rare earth based magnet, comprising,
R 2 T 14 B major phase crystal grains and crystal boundary phases, wherein, said crystal boundary phases include crystal boundary phases containing at least R, T and M with the relative atomic ratios of R, T and M in the following ranges,
R: 60 to 80%,
T: 15 to 35%, and,
M: 1 to 20%,
wherein, R represents the rare earth element, T represents at least one iron family element with Fe as essential, and M represents at least one element selected from the group consisting of Al, Ge, Si, Sn and Ga,
in said crystal boundary phases containing at least R, T and M, when the numbers of R, T and M atoms are respectively referred to as [R], [T] and [M], [R]/[M]<25 and [T]/[M]<10,
the rare earth based magnet contains Cu,
amounts of each element relative to a total mass is as follows:
R: 29.5 to 33 mass %;
B: 0.7 to 0.95 mass %;
M: 0.03 to 1.5 mass %;
Cu: 0.01 to 1.5 mass %;
Fe: balance, substantially; and
a total content of elements other than Fe occupying the balance: 5 mass % or less,
a sum of heavy rare earth elements accounts for 0.5 mass % or less based on the total mass of the rare earth based magnet, and
an absolute value of a demagnetization rate at a high temperature is inhibited to 3% or less.
2. The rare earth based magnet of claim 1 , wherein, said crystal boundary phases containing at least R, T and M are R-T-M based compounds.
3. The rare earth based magnet of claim 2 , wherein, an area ratio of the R-T-M based compound relative to a total base material ranges from a level above 0.1% to a level less than 10% at any section having about 200 main phase grains.
4. The rare earth based magnet of claim 2 , wherein, said R-T-M based compound is a crystal belonging to the cubic crystal system.
5. The rare earth based magnet of claim 2 , wherein, said R-T-M based compound is a crystal having body centered cubic lattices.
6. The rare earth based magnet of claim 2 , wherein, in said R-T-M based compound, the length of the a axis in the unit lattice is 11 to 13 Å.
7. The rare earth based magnet of claim 1 , wherein,
the rare earth based magnet contains Nd, Pr, B, C, and M, and
the numbers of Nd, Pr, B, C, and M atoms contained in the rare earth based magnet are referred to as [Nd], [Pr], [B], [C] and [M], in which
0.27<[B]/([Nd]+[Pr])<0.40 and 0.07<([M]+[C])/[B]<0.60.
8. The rare earth based magnet of claim 1 , wherein,
the rare earth based magnet contains O, C, and N, and
the numbers of O, C, and N atoms contained in the rare earth based magnet are referred to as [O], [C], and [N], in which
[O]/([C]+[N])<0.60.
9. The rare earth based magnet of claim 1 , wherein,
[R]/[M]<18.6 and [T]/[M]<6.9.
10. The rare earth based magnet of claim 1 , wherein,
the amounts of each element relative to the total mass is as follows:
R: 30.5 to 32.0 mass %;
B: 0.83 to 0.90 mass %;
M: 0.4 to 0.8 mass %;
Cu: 0.1 to 0.3 mass %;
Fe: balance, substantially; and
the total content of elements other than Fe occupying the balance: 5 mass % or less.
11. The rare earth based magnet of claim 1 , wherein,
the crystal boundary phases contain at least R, T and M with the relative atomic ratios of R, T and M in the following ranges,
R: 66.1 to 70.2%,
T: 21.5 to 26.1%, and,
M: 3.8 to 10.8%.