Oxide magnetic material

1. An oxide magnetic material including, as a main phase, a ferrite having a hexagonal M-type magnetoplumbite structure, the material comprising:

A, which is at least one element that is selected from the group consisting of Sr, Ba, Pb and Ca;

R, which is at least one element that is selected from the group consisting of Y (yttrium), the rare earth elements and Bi;

Fe; and

B (boron),

wherein the constituents A, R, Fe and B of the oxide magnetic material satisfy the inequalities of:

7.04 at %≦A≦8.68 at %;

0.07 at %≦R≦0.44 at %;

90.4 at %≦Fe≦92.5 at %; and

0.015 at %≦B≦0.87 at %

with respect to the sum of the elements A, R, Fe and B; and

wherein the material is represented by the general formula:

(1−x)AO.(x/2)R 2 O 3 .n(Fe 2 O 3 ).y(B 2 O 3 )

where 0.01≦x≦0.05, 0.001≦y≦0.05, and 5.2≦n≦6.2.

2. A ferrite magnet powder including the oxide magnetic material of claim 1 .

3. A sintered magnet, which is made of the ferrite magnet powder of claim 2 and which includes CaO, SiO 2 , CoO, Cr 2 O 3 , Al 2 O 3 , SrO and BaO at the percentages of:

0.3 wt % to 1.5 wt % (CaO),

0.2 wt % to 1.0 wt % (SiO 2 ),

0 wt % to 0.4 wt % (CoO),

0 wt % to 5.0 wt % (Cr 2 O 3 ),

0 wt % to 5.0 wt % (Al 2 O 3 ),

0 wt % to 3.0 wt % (SrO), and

0 wt % to 3.0 wt% (BaO), respectively.

4. A method of making a ferrite calcined body, the method comprising the steps of:

preparing a material powder mixture by mixing:

a material powder of at least one compound that is selected from the group consisting of SrCO 3 , BaCO 3 , PbO and CaCO 3 ;

a material powder of at least one oxide that is selected from the group consisting of an oxide of Y, oxides of the rare earth elements and Bi 2 O 3 ; a material powder of Fe 2 O 3 (iron oxide); and

a material powder of B 2 O 3 or H 3 BO 3 ; and

calcining the material powder mixture at a temperature of 1,100° C. to 1,300° C., thereby forming a ferrite calcined body having a composition represented by the general formula:

 (1−x)AO.(x/2)R 2 O 3 .n(Fe 2 O 3 ).y(B 2 O 3 )

where A is at least one element selected from the group consisting of Sr, Ba, Pb and Ca; R is at least one element selected from the group consisting of the rare earth elements, including Y, and Bi; 0.01≦x≦0.05; 0.001≦y≦0.05; and 5.2≦n≦6.2.

5. The method of claim 4 , further comprising the step of preparing the material powder of Fe 2 O 3 (Iron oxide) having a particle size of 0.5 μm to 0.8 μm when the size is measured by an air permeability method.

6. A method of making a magnet powder, the method comprising the steps of:

preparing a calcined body mixed powder by adding 0.3 wt % to 1.5 wt % of CaCO 3 , 0.2 wt % to 1.0 wt % of SiO 2 , 0 wt % to 0.4 wt % of CoO, 0 wt % to 0.4 wt % of cobalt hydroxide, 0 wt % to 5.0 wt % of Cr 2 O 3 , 0 wt % to 5.0 wt % of Al 2 O 3 , 0 wt % to 3.0 wt % of SrCO 3 and 0 wt % to 3.0 wt % of BaCO 3 to the calcined body that has been made by the method of claim 4 ; and

pulverizing the calcined body mixed powder to obtain a ferrite pulverized powder having a mean particle size of 0.5 μm to 1.5 μm when the size is measured by an air permeability method.

7. The method of claim 6 , further comprising the step of obtaining the ferrite pulverized powder having a mean particle size of 0.8 μm to 1.3 μm when the size is measured by the air permeability method.

8. A method of producing a sintered magnet, the method comprising the steps of:

preparing a material powder mixture by mixing:

a material powder of at least one compound that is selected from the group consisting of SrCO 3 , BaCO 3 , PbO and CaCO 3 ;

a material powder of at least one oxide that is selected from the group consisting of an oxide of Y, oxides of the rare earth elements and Bi 2 O 3 ;

a material powder of Fe 2 O 3 (iron oxide); and

a material powder of B 2 O 3 or H 3 BO 3 ; and

calcinlng the material powder mixture at a temperature of 1,100° C. to 1.300° C., thereby forming a ferrite calcined body having a composition represented by the general formula:

(1−x)AO.(x/2)R 2 O 3 .n(Fe 2 O 3 ).y(B 2 O 3 )

where A is at least one element selected from the group consisting of Sr, Ba, Pb and Ca; R is at least one element selected from the group consisting of the rare earth elements, including Y, and Bi; 0.01≦x≦0.05; 0.001≦y≦0.05; and 5.2≦n≦6.2;

preparing a calcined body mixed powder by adding 0.3 wt % to 1.5 wt % of CaCO 3 , 0.2 wt % to 1.0 wt % of SIO 2 , 0 wt % to 4.0 wt % of CoO, 0 wt % to 0.4 wt % of cobalt hydroxide, 0 wt % to 5.0 wt % of Cr 2 O 3 , 0 wt % to 5.0 wt % of Al 2 O 3 , 0 wt % to 3.0 wt % of SrCO 3 and 0 wt % to 3.0 wt % of BaCO 3 to the ferrite calcined body;

pulverizing the calcined body mixed powder in an aqueous solvent, thereby obtaining a slurry of a ferrite pulverized powder having a mean particle size of 0.5 μm to 1.5 μm when the size is measured by an air permeability method; and

condensing, mulling, compacting and sintering the slurry, where the slurry is compacted with or without a magnetic field applied thereto.

9. The method of claim 8 , wherein the step of pulverizing or the step of mulling includes the step of adding a dispersant at a solid matter ratio of 0.1 wt % to 2.0 wt %.

10. The method of claim 8 , wherein the step of sintering is carried out at a temperature of 1,230° C. or more.

11. A sintered magnet produced by the method of claim 8 .

12. A sintered magnet that is produced by the method of claim 8 and that has a density of 5.02 Mg/m 3 or more.

13. A sintered magnet that is produced by the method of claim 8 and that has a loop squareness of 95% or more.

14. A rotating machine comprising the sintered magnet of claim 3 .