Iron-based oxide magnetic particle powder, method for producing same, coating material, and magnetic recording medium

A method for producing iron-based oxide magnetic particle powder comprising ε-Fe2O3 having an average particle diameter measured with a transmission electron microscope of 10 nm or more and 30 nm or less, a part of Fe sites of which is substituted by another metal element,

• the method comprising:
• a first neutralization step of neutralizing an aqueous solution containing a trivalent iron ion and an ion of the metal substituting a part of the Fe sites to make pH of 1.5 or more and 2.5 or less at a temperature retained at 5° C. or more and 25° C. or less;
• adding a hydroxycarboxylic acid to the aqueous solution after neutralizing, at a temperature retained at 5° C. or more and 25° C. or less;
• a second neutralization step of neutralizing the aqueous solution to make pH of 8.0 or more and 9.0 or less at a temperature retained at 5° C. or more and 25° C. or less after adding the hydroxycarboxylic acid;
• rinsing a formed precipitate of iron oxyhydroxide containing the substituting metal element formed in the second neutralization step, with water;
• coating a silicon oxide on the iron oxyhydroxide containing the substituting metal element after rinsing with water;
• and
• heating the iron oxyhydroxide containing the substituting metal element coated with the silicon oxide to provide an iron oxide containing the substituting metal element coated with the silicon oxide.

A method for producing iron-based oxide magnetic particle powder comprising ε-Fe2O3 having an average particle diameter measured with a transmission electron microscope of 10 nm or more and 30 nm or less, a part of Fe sites of which is substituted by another metal element,

• the method comprising:
• a first neutralization step of neutralizing an aqueous solution containing a trivalent iron ion and an ion of the metal substituting a part of the Fe sites to make pH of 1.5 or more and 2.5 or less at a temperature retained at 5° C. or more and 25° C. or less;
• adding a hydroxycarboxylic acid to the aqueous solution after neutralizing, at a temperature retained at 5° C. or more and 25° C. or less;
• a second neutralization step of neutralizing the aqueous solution to make pH of 8.0 or more and 9.0 or less at a temperature retained at 5° C. or more and 25° C. or less after adding the hydroxycarboxylic acid;
• rinsing a formed precipitate of iron oxyhydroxide containing the substituting metal element formed in the second neutralization step, with water;
• subjecting the iron oxyhydroxide containing the substituting metal element after rinsing with water, to a hydrothermal treatment at 120° C. or more and 180° C. or less;
• coating a silicon oxide on the iron oxyhydroxide containing the substituting metal element after subjecting to the hydrothermal treatment;
• and
• heating the iron oxyhydroxide containing the substituting metal element coated with the silicon oxide to provide an iron oxide containing the substituting metal element coated with the silicon oxide.