The magnetic powder for a radio wave absorber is a powder of a hexagonal ferrite having a composition represented by Formula 1, a region B is present on the particle surface of the powder, and Expression 2: 0.3≤content of A atom in region B/content of Al atom in region B≤23.0 and Expression 3: 1.2≤total of content of A atom and content of Al atom in region B/total of content of A atom and content of Al atom in entire powder≤2.5 are satisfied. The region B is a region that is observed as a bright region having a long side diameter of 0.1 μm to 0.6 μm in an image subjected to binarization processing. A represents one or more kinds of atoms (A atom) selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 0.10≤x≤5.00.

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

Aluminium-containing iron oxide pigments of the formula Fe.sub.2-xAl.sub.xO.sub.3 with x values from 0.01 to 0.25, characterized in that they possess an a* value of 30.5 to 32.5 CIELAB units and a b* value of 25.5 to 30.5 CIELAB units, measured in each case as full shade in the alkyd resin according to DIN EN ISO 787-25:2007.

A method for producing a solid composition according to the present disclosure includes producing an oxide to be converted into a first functional ceramic by reacting with an oxoacid compound, and mixing the oxide, the oxoacid compound, and a second functional ceramic that is different from the first functional ceramic. The oxoacid compound preferably contains at least one of a nitrate ion and a sulfate ion as an oxoanion.

An iron oxide powder which has an aluminum content of from 10 mol % to 80 mol % (inclusive), and which is composed of porous structures that have a diameter of from 0.3 μm to 2 μm (inclusive).

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.

A radio wave absorber includes a base member, and a radio wave absorption film formed on the base member. The radio wave absorption film includes at least MTC-substituted ε-Fe.sub.2O.sub.3 and black titanium oxide. The MTC-substituted ε-Fe.sub.2O.sub.3 is a crystal belonging to the same space group as an ε-Fe.sub.2O.sub.3 crystal and expressed by ε-M.sub.xTi.sub.yCo.sub.yFe.sub.2−2y−xO.sub.3 where M is at least one element selected from the group consisting of Ga, In, Al, and Rh, 0<x<1, and 0<y<1.

The powder of the magnetoplumbite-type hexagonal ferrite is an aggregate of particles of a compound represented by Formula (1), and, in a particle size distribution based on number measured by a laser diffraction scattering method, in a case where a mode value is defined as a mode diameter, a diameter at a cumulative percentage of 10% is defined as D10 and a diameter at a cumulative percentage of 90% is defined as D90, the mode diameter is equal to or greater than 5 μm and less than 10 μm and an expression of (D90−D10)/mode diameter≤3.0 is satisfied. 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 powder mixture of a magnetoplumbite-type hexagonal ferrite is a mixture of powders of two or more kinds of compounds represented by Formula (1), the two or more kinds of compounds represented by Formula (1) are two or more kinds of compounds having different values of x in Formula (1), and are a powder mixture satisfying a relationship of x.sub.max-x.sub.min23 0.2, in a case where a maximum value of x is defined as x.sub.max and a minimum value of x is defined as x.sub.min, in two or more kinds of compounds having different values of x in Formula (1), 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)

Aluminium-containing iron oxide pigments of the formula Fe.sub.2-xAl.sub.xO.sub.3 with x values from 0.01 to 0.25, characterized in that they possess an a* value of 30.5 to 32.5 CIELAB units and a b* value of 25.5 to 30.5 CIELAB units, measured in each case as full shade in the alkyd resin according to DIN EN ISO 787-25: 2007.

Magnetic powder includes: at least one epsilon-phase iron oxide-based compound selected from the group consisting of -Fe.sub.2O.sub.3 and a compound represented by Formula (1); and a surface treatment layer including a silane compound on at least a part of a surface. The magnetic powder has an average particle diameter of 8 nm to 20 nm. The content ratio of carbon atoms of the silane compound included in the surface treatment layer to iron atoms of the at least one epsilon-phase iron oxide-based compound selected from the group consisting of -Fe.sub.2O.sub.3 and the compound represented by Formula (1) is 0.05% to 0.5% in terms of the number of atoms. A manufacturing method thereof and applications thereof are also provided. In Formula (1), A represents at least one metal element other than Fe and a represents a number that satisfies a relationship of 0<a<2.
-A.sub.aFe.sub.2-aO.sub.3(1)