Rare earth magnet
A rare earth magnet having a main phase and a sub-phase, wherein the main phase has a ThMn 12 -type crystal structure; the sub-phase contains at least any one of an Sm 5 Fe 17 -based phase, an SmCo 5 -based phase, an Sm 2 O 3 -based phase, and an Sm 7 Cu 3 -based phase; assuming that the volume of the rare earth magnet is 100%, the volume fraction of the sub-phase is from 2.3 to 9.5% and the volume fraction of an α-Fe phase is 9.0% or less; and the density of the rare earth magnet is 7.0 g/cm 3 or more.
1. A rare earth magnet comprising a main phase and a sub-phase,
wherein the main phase has a ThMn 12 -type crystal structure,
wherein the sub-phase contains at least any one of an Sm 5 Fe 17 -based phase, an SmCo 5 -based phase, an Sm 2 O 3 -based phase, and an Sm 7 Cu 3 -based phase,
wherein the volume fraction of the sub-phase is from 2.3 to 9.5% and the volume fraction of an α-Fe phase is 9.0% or less, when the volume of the rare earth magnet is 100%, and
wherein the density of the rare earth magnet is 7.0 g/cm 3 or more.
2. The rare earth magnet according to claim 1 , wherein part of Fe of the Sm 5 Fe 17 -based phase is replaced by Ti.
3. The rare earth magnet according to claim 2 , wherein the Sm 5 Fe 17 -based phase contains an Sm 5 (Fe 0.95 Ti 0.05 ) 17 phase.
4. The rare earth magnet according to claim 1 , wherein part of Co of the SmCo 5 -based phase is replaced by Cu.
5. The rare earth magnet according to claim 4 , wherein the SmCo 5 -based phase contains an Sm(Co 0.3 Cu 0.2 ) 5 phase.
6. The rare earth magnet according to claim 1 , wherein the composition of the main phase is represented by the formula:
(R 1 (1-x) R 2 x ) a (Fe (1-y) Co y ) b T c M d
(wherein
R 1 is one or more rare earth elements selected from the group consisting of Sm, Pm, Er, Tm and Yb,
R 2 is one or more elements selected from the group consisting of Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho and Lu,
T is one or more elements selected from the group consisting of Ti, V, Mo, Si, Al, Cr and W,
M is one or more elements selected from the group consisting of Cu, Ga, Ag and Au, and unavoidable impurity elements,
0≤ x≤ 0.5,
0≤ y≤ 0.8,
4.0≤ a≤ 9.0,
b= 100− a−c−d,
3.0≤ c≤ 7.0, and
0≤ d≤ 3.0).
7. The rare earth magnet according to claim 1 , wherein the Sm 5 Fe 17 -phase, the SmCo 5 -phase, the Sm 2 O 3 -phase, and the Sm 7 Cu 3 -phase contain an Sm 5 Fe 17 phase, an SmCo 5 phase, an Sm 2 O 3 phase, and an Sm 7 Cu 3 phase, respectively.
8. The rare earth magnet according to claim 7 , wherein the Sm 7 Cu 3 -based phase contains a phase having mixed therein an Sm phase and an SmCu phase in a ratio of 3:4.
9. The rare earth magnet according to claim 8 , wherein the Sm phase contains a crystal phase and an amorphous Sm phase.