A ferrite sintered magnet 100 comprises M-type ferrite crystal grains 4 having a hexagonal structure, two-crystal grain boundaries 6a formed between two of the M-type ferrite crystal grains 4, and multiple-crystal grain boundaries 6b surrounded by three or more of the M-type ferrite crystal grains 4. This ferrite sintered magnet 100 contains at least Fe, Ca, B, and Si, and contains B in an amount of 0.005 to 0.9 mass % in terms of B.sub.2O.sub.3, the two-crystal grain boundaries 6a and the multiple-crystal grain boundaries 6b contain Si and Ca, and in a cross-section parallel to a c-axis of the ferrite sintered magnet, when the number of multiple-crystal grain boundaries 6b having a maximum length of 0.49 to 5 μm per cross-sectional area of 76 μm.sup.2 is N, N is 7 or less.

A grain-oriented M-type hexagonal ferrite has the formula MeFe.sub.12O.sub.19, and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or a cone anisotropy, in the hexagonal crystallographic structure wherein Me is Sr.sup.+, Ba.sup.2+ or Pb.sup.2+, and wherein greater than 30%, preferably greater than 80%, of c-axes of the ferrite grains are aligned perpendicular to the c-plane.

Disclosed herein are embodiments of composite hexagonal ferrite materials formed from a combination of Y phase and Z phase hexagonal ferrite materials. Advantageously, embodiments of the material can have a high resonant frequency as well as a high permeability. In some embodiments, the materials can be useful for magnetodielectric antennas.

A ferrite sintered magnet comprising an M type Sr ferrite having a hexagonal structure as a main phase, wherein the ferrite sintered magnet does not substantially comprise a rare earth element and Co, a content of B is 0.005 to 0.9% by mass in terms of B.sub.2O.sub.3, and a content of Zn is 0.01 to 1.2% by mass in terms of ZnO.

Provided is a red mud-based composite calcium ferrite and a preparation method and use thereof. The preparation method of the red mud-based composite calcium ferrite includes the following steps: mixing red mud and a calcium source, and roasting an obtained mixture in an oxygen-containing atmosphere to obtain the red mud-based composite calcium ferrite; where the calcium source is selected from the group consisting of lime and calcium carbonate. In the present disclosure, the composite calcium ferrite is prepared using a solid waste red mud, with a greatly reduced cost of raw materials; on the other hand, compared with traditional calcium ferrite, the composite calcium ferrite mainly has phase structures of CaFe.sub.2O.sub.4, Ca.sub.2FeAlO.sub.5, and Ca.sub.2Fe.sub.2O.sub.5. Therefore, the composite calcium ferrite has a lower melting point, a higher lime dissolution efficiency, and better fluxing and dephosphorization effects during primary smelting and refining of molten steel, and has broad prospects for use in industry.

A ferrite sintered magnet 100 comprises M-type ferrite crystal grains 4 and multiple-crystal grain boundaries 6b surrounded by three or more of the M-type ferrite crystal grains 4. The ferrite sintered magnet 100 contains at least Fe, Ca, B, and Si, and contains 0.005 to 0.9 mass % of B in terms of B.sub.2O.sub.3. The multiple-crystal grain boundaries 6b contain Si and Ca, and in a case where the molar ratio of Ca to Si in the multiple-crystal grain boundaries 6b is represented by (Ca/Si).sub.G, the following formula is satisfied.
0.1<(Ca/Si).sub.G<0.9

Provided is a ferrite sintered magnet including: magnetoplumbite type ferrite crystal grains; and a two-grain boundary interposed between the ferrite crystal grains. The two-grain boundary contains Ca and La, and an atomic ratio Ca/La at the two-grain boundary is 0.3 to 3.0.

There is provided a ferrite powder for bonded magnets capable of producing ferrite bonded magnets with high BH.sub.max, excellent in MFR when converted to a compound, with high p-iHc, wherein an average particle size of particles obtained by a dry laser diffraction measurement is 5 μm or less, a specific surface area is 1.90 m.sup.2/g or more and less than 3.00 m.sup.2/g, a compression density is 3.40 g/cm.sup.3 or more and less than 3.73 g/cm.sup.3, and a compressed molding has a coercive force of 2800 Oe or more and less than 3250 Oe.

A polycrystalline fused product based on brownmillerite, includes, for more than 95% of its weight, of the elements Ca, Sr, Fe, O, M and M′, the contents of the elements being defined by the formula X.sub.yM.sub.zFe.sub.tM′.sub.uO.sub.2.5, wherein the atomic indices are such that 0.76≤y≤1.10, z≤0.21, 0.48≤t≤1.15 and u≤0.52, 0.95≤y+z≤1.10, and 0.95≤t+u≤1.10, X being Ca or Sr or a mixture of Ca and Sr, M being an element chosen from the group formed by La, Ba and mixtures thereof, M′ being an element chosen from the group formed by Ti, Cu, Gd, Mn, Al, Sc, Ga, Mg, Ni, Zn, Pr, In, Co, and mixtures thereof, the sum of the atomic indices of Ti and Cu being less than or equal to 0.1.

A ferrite sintered magnet contains a main phase formed of ferrite having a hexagonal magnetoplumbite type crystalline structure; a first subphase containing La, Ca, and Fe, in which an atomic ratio of La is higher than that of the main phase, and the atomic ratio of La is higher than an atomic ratio of Ca; and a second subphase containing La, Ca, Si, B, and Fe, in which an atomic ratio of Ca is higher than an atomic ratio of La, an atomic ratio of B is higher than an atomic ratio of Fe, and the atomic ratio of Fe is lower than that of the main phase. An area ratio of the second subphase on a cross-sectional surface of the ferrite sintered magnet is greater than or equal to 1%.