Substitution-type epsilon-iron oxide magnetic particle powder, method for producing substitution-type epsilon-iron oxide magnetic particle powder, green compact, method for producing green compact, and electromagnetic wave

A method for producing a substitution-type ε-iron oxide magnetic particle powder mainly containing an ε-type iron-based oxide in which the Fe sites of ε-Fe2O3 are partially substituted by another metal element, the method comprising:

• a neutralization step of obtaining a dispersion liquid containing an iron oxyhydroxide having a substituent metal element or a mixture of an iron oxyhydroxide and a hydroxide of a substituent metal element using an acidic aqueous solution containing a trivalent iron ion and an ion of a metal that partially substitutes the Fe sites as a raw material solution by adding an alkali to the raw material solution so as to neutralize the solution to a pH of 8.0 or higher and 10.0 or lower;
• a silicon compound addition step of adding a silicon compound having a hydrolyzable group to the dispersion liquid containing the iron oxyhydroxide having a substituent metal element or the mixture of the iron oxyhydroxide and the hydroxide of a substituent metal element;
• and
• an aging step of coating the iron oxyhydroxide having a substituent metal element or the mixture of the iron oxyhydroxide and the hydroxide of a substituent metal element with a chemical reaction product of the silicon compound by holding the dispersion liquid containing the iron oxyhydroxide having a substituent metal element or the mixture of the iron oxyhydroxide and the hydroxide of a substituent metal element, and the silicon compound at a pH of 8.0 or higher and 10.0 or lower, wherein
• the addition of the silicon compound having a hydrolyzable group is started when the pH of the dispersion liquid in the neutralization step has reached 2.0 or higher and 7.0 or lower,
• when the number of moles of the silicon compound to be added to the dispersion liquid with a pH of 2.0 or higher and 7.0 or lower is represented by S1, the number of moles of Fe ions contained in the raw material solution is represented by F, and the total number of moles of substituent metal element ions therein is represented by M, S1/(F+M) is 0.01 or more and 10.0 or less, and
• when the total number of moles of the silicon compound added is represented by S2, S2/(F+M) is 0.50 or more and 10.0 or less.