Calcined ferrite, and sintered ferrite magnet and its production method

1. A sintered ferrite magnet having a composition of metal elements of Ca, R, A, Fe and Co, which is represented by the general formula of Ca 1-x-y′ R x A y′ Fe 2n-z Co z , wherein R is at least one of rare earth elements indispensably including La; A is Sr; x, y′, z and n represent the atomic ratios of Ca, R, A, Fe and Co; 2n represents a molar ratio expressed by 2n=(Fe+Co)/(Ca+R+A); and x, y′, z and n meet the following conditions:

0.425≤(1− x−y ′)≤0.55,

0.15≤ x≤ 0.35,

0.05≤ y′≤ 0.40,

(1− x−y′ )> y′,

0< z≤ 0.18, and

7.5≤(2 n−z )<11.0,

wherein said sintered ferrite magnet further contains more than 0% and 1.0% or less by mass of Si as SiO 2 .

2. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio (1−x−y′) meets 0.425>(1−x−y′)≤0.50.

3. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio y′ meets 0.20≤y′≤0.40.

4. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio y′ meets 0.20≤y′≤0.35.

5. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio z meets 0≤z≤0.17.

6. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio z meets 0≤z≤0.15.

7. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio (2n−z) meets 7.5≤(2n−z)≤10.5.

8. The sintered ferrite magnet according to claim 1 , wherein said atomic ratio (2n−z) meets 7.5≤(2n−z)≤10.0.

9. The sintered ferrite magnet according to claim 1 , wherein said atomic ratios z and (2n−z) meet 0.0084≤z/(2n−z)≤0.0167.

10. A method for producing the sintered ferrite magnet recited in claim 1 , comprising the steps of

mixing raw material powders containing metal elements of Ca, R, A, Fe and Co to prepare a raw material powder mixture having a metal element composition represented by the general formula of Ca 1−x−y′ R x A y′ Fe 2n-z Co z , wherein R is at least one of rare earth elements indispensably including La; A is Sr; x, y′, z and n represent the atomic ratios of Ca, R, A, Fe and Co; 2n represents a molar ratio expressed by 2n=(Fe+Co)/(Ca+R+A); and x, y′, z and n meet the following conditions:

0.425≤(1− x−y ′)≤0.55,

0.15≤ x≤ 0.35,

0.05≤ y′≤ 0.40,

(1− x−y′ )> y′,

0< z≤ 0.18, and

9.0≤2 n−z )<11.0,

calcining the resultant raw material powder mixture,

pulverizing the resultant calcined body,

molding the resultant calcined body powder, and

sintering the resultant green body,

wherein more than 0% and 1.0% or less by mass of SiO 2 is added to 100% by mass of said calcined body or calcined body powder, after said calcining step and before said molding step.

11. The method for producing a sintered ferrite magnet according to claim 10 , wherein more than 0% and 1.5% or less by mass of CaCO 3 as CaO is further added to 100% by mass of said calcined body or calcined body powder, after said calcining step and before said molding step.

12. The method for producing a sintered ferrite magnet according to claim 10 , wherein more than 0% and 0.7% or less by mass of CaCO 3 as CaO is further added to 100% by mass of said calcined body or calcined body powder, after said calcining step and before said molding step.

13. The method for producing a sintered ferrite magnet according to claim 10 , wherein said atomic ratio (1−x−y′) meets 0.425≤(1−x−y′)≤0.50.

14. The method for producing a sintered ferrite magnet according to claim 10 , wherein said atomic ratio z meets 0<z≤0.15.

15. The method for producing a sintered ferrite magnet according to claim 10 , wherein said atomic ratios z and (2n−z) meet 0.0084≤z/(2n−z)≤0.0167.