There is provided a radio wave absorber including a powder of a hexagonal ferrite; and a binder, in which the radio wave absorber has a squareness ratio in a range of 0.40 to 0.60.

There is provided a radio wave absorber including a magnetic powder and a binder, in which a volume filling rate of the magnetic powder in the radio wave absorber is 35% by volume or less, a transmission attenuation amount is 8.0 dB or more, and a reflection attenuation amount is 8.0 dB or more.

There is provided a radio wave absorber including a magnetic powder and a binder, in which a volume filling rate of the magnetic powder in the radio wave absorber is 35% by volume or less, and a volume filling rate of a carbon component in the radio wave absorber is 0% by volume or more and 2.0% by volume or less.

A magnetoplumbite-type hexagonal ferrite powder containing a powder of a magnetoplumbite-type hexagonal ferrite represented by Formula (1) and a powder of a compound represented by Formula (2), in which a magnetic field strength Hα, which corresponds to 90% of a magnetization quantity obtained in a case where an external magnetic field of 50 kOe is applied, satisfies 19 kOe≤Hα≤28 kOe, a radio wave absorber, and a method of controlling resonance frequency of a magnetoplumbite-type hexagonal ferrite powder are provided. In Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5≤x≤8.0. In Formula (2), A.sup.a represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb.

AFe.sub.(12-x)Al.sub.xO.sub.19  Formula (1)

A.sup.aAl.sub.2O.sub.4  Formula (2)

There is provided a radio wave absorbing composition containing a magnetic powder and a binder. There is also provided a radio wave absorber containing a magnetic powder and a binder. The magnetic powder is a powder of a substitution-type hexagonal ferrite subjected to surface treatment with a surface treatment agent, and the binder is a polyamide.

There is provided a radio wave absorbing composition containing a magnetic powder and a binder. There is also provided a radio wave absorber containing a magnetic powder and a binder. The magnetic powder is a powder of a substitution-type hexagonal ferrite subjected to surface treatment with a surface treatment agent, the surface treatment agent is a silicon-based compound, and the binder is an olefin-based resin.

There are provided a magnetoplumbite-type hexagonal crystal ferrite magnetic powder which can be suitably used as the material of a radio wave absorber having an excellent radio wave absorbing power in the 76 GHz band, and a method for producing the same. In a method for producing a magnetoplumbite-type hexagonal crystal ferrite magnetic powder, the method comprising the steps of: mixing powders of the raw materials of a magnetoplumbite-type hexagonal crystal ferrite magnetic powder, which is expressed by a compositional formula of AFe.sub.(12-x)Al.sub.xO.sub.19 (A is at least one selected from the group consisting of Sr, Ba, Ca and Pb, x=1.0 to 2.2), to obtain a mixture; granulating and molding the mixture to obtain molded bodies; firing the molded bodies to obtain fired bodies; and pulverizing the fired bodies, there are prepared a plurality of firing containers (firing scabbards 10), each of which has an opening of the upper face thereof and a notch (10a) formed in the upper portion of the side face thereof so as to be communicated with the outside thereof, each of the firing containers being filled with the molded bodies, and the firing containers being stacked in a plurality of stages so as to close the opening of the top face of the lower firing container, to fire the molded bodies in a firing furnace (20).

To provide magnetoplumbite-type hexagonal ferrite particles represented by Formula (1) and having a single crystal phase, and the application. In Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5≤x≤8.0.
AFe.sub.(12−x)Al.sub.xO.sub.19  Formula (1)

A method for producing a solid composition according to the present disclosure is a method for producing a solid composition that is used for forming a functional ceramic having a first crystal phase. The method for producing a solid composition includes: producing an oxide composed of a second crystal phase different from the first crystal phase; and mixing the oxide and an oxo acid compound.

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.