HEXAGONAL FERRITE MAGNETIC POWDER, METHOD FOR PRODUCING THE SAME, MAGNETIC POWDER FOR MAGNETIC RECORDING MEDIUM, AND MAGNETIC RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a hexagonal ferrite magnetic powder permitting ultrahigh-density recording by a glass crystallization method.SOLUTION: The method for producing a hexagonal ferrite magnetic powder comprises: melting in a melting tank a starting material mixture comprising a glass-forming component and a hexagonal ferrite-forming component; discharging a melt from the melting tank and supplying it between a pair of rotating milling rollers positioned beneath the melting tank; discharging an amorphous material from a space between the rollers by roll-quenching the melt that has been supplied between the milling rollers; subjecting the amorphous material to heat treatment to cause hexagonal ferrite magnetic particles to precipitate; and collecting the hexagonal ferrite magnetic particles precipitated from a substance obtained by the heat treatment, wherein at least an outermost layer portion of the milling rollers is comprised of a material with a Young's modulus of equal to or higher than 500 GPa and Rockwell hardness of equal to or higher than 85.0 HRA, the outermost layer portion has a thickness of equal to or greater than 5 mm and the milling rollers have surface roughness of equal to or less than 0.5 μm.