Abstract: A raw material solution containing trivalent iron ions, or trivalent iron ions and ions of a metal element that partially substitutes Fe sites, and an alkaline aqueous solution for neutralizing the raw material solution are added to a reaction system to adjust the pH of the reaction system from 1.0 to 3.0 or lower. Hydroxycarboxylic acid is added to the obtained reaction solution and the pH of the reaction system is then neutralized from 7.0 to 10.0 or lower. The obtained precipitate of a substituent metal element-containing iron oxyhydroxide is coated with silicon oxide, followed by heating so as to form particles of ?-iron oxide in which Fe sites are partially substituted by other metal elements, and then, a slurry containing the particles is classified. The iron-based oxide magnetic powder has a particle shape close to a perfect sphere and is suitable for use in a magnetic recording medium.

Abstract: A method for making an iron-based oxide magnetic powder includes adding raw material solution containing trivalent iron ions, or trivalent iron ions and ions of a metal element that partially substitutes Fe sites, and an alkaline aqueous solution for neutralizing the raw material solution to a reaction system to adjust the pH of the reaction system to 1.0 or higher and 3.0 or lower. Hydroxycarboxylic acid is added to the obtained reaction solution and thereafter the pH of the reaction system is neutralized to 7.0 or higher and 10.0 or lower. The obtained precipitate of a substituent metal element-containing iron oxyhydroxide is coated with silicon oxide and then heated, whereby an iron-based oxide magnetic powder is obtained with a reduced content of fine and coarse particles, a particle shape close to a perfect sphere, and particles of ?-iron oxide in which Fe sites are partially substituted by other metal elements.

Abstract: An object of the present invention is to provide a magnetic powder having a narrow particle size distribution of epsilon-type iron oxide particles, and another object is to provide magnetic powder suitable for magnetic recording medium by improving particle size distribution, and provide epsilon-type iron oxide magnetic particles and related technologies in which a number average particle diameter of major diameters (D50) is 10 to 20 nm, a 90% cumulative particle diameter (D90) is 30 nm or less, and a geometric standard deviation (?g) of major diameters is 1.45 or less, which are obtained by TEM observation.

Abstract: An object of the present invention is to provide a magnetic powder having a narrow particle size distribution of epsilon-type iron oxide particles, and another object is to provide magnetic powder suitable for magnetic recording medium by improving particle size distribution, and provide epsilon-type iron oxide magnetic particles and related technologies in which a number average particle diameter of major diameters (D50) is 10 to 20 nm, a 90% cumulative particle diameter (D90) is 30 nm or less, and a geometric standard deviation (?g) of major diameters is 1.45 or less, which are obtained by TEM observation.