Patent ID: 8840802

Claim:
A method of manufacturing hexagonal ferrite magnetic powder, which comprises: preparing a melt by melting a starting material mixture comprising a hexagonal ferrite-forming component and a glass-forming component and rapidly cooling the melt to obtain a solidified product, heating the solidified product to precipitate hexagonal ferrite magnetic particles and crystallized glass components in the solidified product, subjecting the solidified product to an acid treatment following the heating to remove the glass components by dissolution, wet processing the hexagonal ferrite magnetic particles obtained following the acid treatment in a water-based solvent to prepare an aqueous magnetic liquid satisfying relation (1) relative to an isoelectric point of the hexagonal ferrite magnetic particles: pH0−pH*≧2.5 (1) where in relation (1), pH0 denotes the isoelectric point of the hexagonal ferrite magnetic particles and pH* denotes a pH of the aqueous magnetic liquid, which is a value of equal to or greater than 2.0, adding a surface-modifying agent comprising an alkyl group and a functional group that becomes an anionic group in the aqueous magnetic liquid to the aqueous magnetic liquid to subject the hexagonal ferrite magnetic particles to a surface-modifying treatment, and removing the water-based solvent following the surface-modifying treatment to obtain hexagonal ferrite magnetic particles, wherein the starting material mixture comprises 1.0 to 10.0 mole percent of Al, based on Al 2 O 3 conversion, relative to a total of the starting material mixture based on oxide conversion, and the wet processing is conducted in a cleaning process with a water-based solvent.