CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2018/019104 filed May 17, 2018, claiming priority based on Japanese Patent Application No. 2017-102245 filed May 24, 2017 and Japanese Patent Application No. 2018-052106 filed Mar. 20, 2018.

FIELD OF THE INVENTION

The present invention relates to a sintered ferrite magnet.

BACKGROUND OF THE INVENTION

Sintered ferrite magnets are extremely chemically stable with excellent cost performance because their main starting material is inexpensive iron oxide, though their maximum energy products are only 1/10 of those of sintered rare earth magnets (for example, sintered NdFeB magnets). Accordingly, their global production is still largest among magnet materials.

Among various applications such as motors, speakers, etc., in which sintered ferrite magnets are used, motors for automobiles, home electric appliances, etc. strongly demand high-performance materials. Because of recent situations in which rare earth materials have been becoming more expensive and suffering more risks of procurement, investigation has been made to use sintered ferrite magnets in industrial motors, motors for driving electric vehicles (EVs, HVs, PHVs, etc.), power generators, etc., in which only sintered rare earth magnets have been used so far.

Typical sintered ferrite magnets are Sr ferrites having a magnetoplumbite structure, whose basic composition is expressed by SrFe12O19. With sintered Sr—La—Co ferrite magnets obtained by substituting part of Sr2+by La3+and part of Fe3+by Co2+in SrFe12O19put into practical use in a latter part of 1990, the magnetic properties of ferrite magnets were drastically improved. In 2007, sintered Ca—La—Co ferrite magnets having further improved magnetic properties were put into practical use. However, to be used in the above applications, sintered Ca—La—Co ferrite magnets need to have higher performance, and improvement in residual magnetic flux densities (hereinafter referred to “Br”) is desired to increase the power of motors in particular applications (for example, motors for home electric appliances).

It is known that Bris improved by substituting part of Co by Zn in sintered Sr—La—Co ferrite magnets (JP 11-154604 A, etc.).

However, the substitution of part of Co by Zn in sintered Sr—La—Co ferrite magnets has not been practically conducted, because it improves Brlittle, while drastically decreasing coercivity (hereinafter referred to as “HcJ”).

OBJECT OF THE INVENTION

Accordingly, an object of the present invention is to provide a sintered ferrite magnet having high Brwith little decrease in HcJ.

SUMMARY OF THE INVENTION

The inventors have found that in the general formula of Ca1-xLaxFe2n-y-zCoyZnzexpressing the atomic ratios of metal elements of Ca, La, Fe, Co and Zn in Japanese Patent Application No. 2017-102245, meeting the following requirements of x, y, z, and n [2n is a molar ratio represented by 2n=(Fe+Co+Zn)/(Ca+La)] provides a sintered ferrite magnet having high Brwith little decrease in HcJ:

0.4≤x≤0.6,

0<y≤0.35,

0<z≤0.35,

0.2≤(y+z)≤0.4, and

3≤n≤6.

As a result of further investigation, the inventors have found that a new composition range partially overlapping the composition range of Japanese Patent Application No. 2017-102245 provides magnetic properties equal to or higher than those obtained by the composition range of Japanese Patent Application No. 2017-102245, proposing the present invention. Incidentally, sintered ferrite magnets described below are illustrative examples of the present invention, and the present invention is not restricted to the composition represented by the above general formula.

Thus, the sintered ferrite magnet of the present invention is represented by the general formula of Ca1-xLaxFe2n-y-zCoyZnzexpressing the atomic ratios of metal elements of Ca, La, Fe, Co and Zn, wherein x, y, z, and n [2n is a molar ratio expressed by 2n=(Fe+Co+Zn)/(Ca+La)] meet

0.4<x<0.75,

0.15≤y<0.4,

0.11≤z<0.4,

0.26≤(y+z)<0.65, and

3≤n≤6.

The above y and z preferably meet 0.15≤y≤0.35, and 0.15≤z≤0.35.

The above x preferably meets 0.475≤x≤0.7.

The above y and z preferably meet 0.26≤(y+z)≤0.6.

The sintered ferrite magnet of the present invention preferably contains 1.8% or less by mass of SiO2.

In the above general formula, part of La may be substituted by at least one of rare earth elements excluding La.

In the above general formula, 50% or less by mol of La may be substituted by at least one of rare earth elements excluding La.

Effects of the Invention

The present invention can provide a sintered ferrite magnet having high Brwith little decrease in HcJ.

