Abstract: The method is: a preparation step in which a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, and a pH adjusting agent are prepared as starting materials; a crystallization step in which a reaction liquid that includes the starting materials and water is prepared, and a crystallized powder that includes the magnetic metals is made to crystallize in the reaction liquid by a reduction reaction; and a recovery step in which the crystallized powder is recovered from the reaction liquid. The magnetic metal source includes a water-soluble iron salt and a water-soluble nickel salt, the nucleating agent is a water-soluble salt of a metal that is more noble than nickel, and the complexing agent is at least one type of substance selected from the group consisting of a hydroxy carboxylic acid, a salt of a hydroxy carboxylic acid, and a derivative of a hydroxy carboxylic acid.