Process for production of magnetic thin film, magnetic thin film, and magnetic material

A process for production of a magnetic thin film, the process comprising:

• producing a mixed solution by mixing a raw-material solution to which calcium ions as a shape control agent are added in the amount of equal to or smaller than 8 wt % with a neutralizer solution to which a neutralizer is added such that a precipitation reaction of ferric-hydroxide-based compound particles progresses in the mixed solution;
• producing silica-coated ferric-hydroxide-based compound particles by adding silane compounds to the mixed solution;
• producing thermally processed powders by separating the silica-coated ferric-hydroxide-based compound particles from the mixed solution and calcining the silica-coated ferric-hydroxide-based compound particles;
• producing magnetic particles by adding the thermally processed powders to an aqueous solution such that silica coating the thermally processed powders is completely eliminated, the magnetic particles being formed of epsilon-type iron-oxide-based compounds, having insulation properties, and serving as a permanent magnet, each magnetic particle being in a rod-like shape having a long-axis size equal to or longer than 100 nm and an aspect ratio equal to or higher than 3.1 and providing a magnetic domain wall therein;
• producing a magnetic material slurry having a ratio of an average particle diameter of the magnetic particles by a dynamic light scattering method to an observed average particle diameter of the magnetic particles by an observation through a transmission electron microscope equal to or less than five by purifying the aqueous solution, in which the magnetic particles are dispersed, with a pH adjustment and a solid content concentration adjustment without a dry process;
• producing a coating liquid having a solution viscosity in a range from 170 cP to 1000 cP by mixing a polymer consisting of polyvinyl-alcohol aqueous solution or PEG aqueous solution with the magnetic material slurry;
• coating a film-formation target with the coating liquid;
• and
• curing the coating liquid coating the film-formation target while applying an external magnetic field with a predetermined intensity to the coating liquid and forming a magnetic thin film, wherein the external magnetic field is continuously applied during a time period until the coating liquid is dried and cured, and wherein
• a ratio of residual magnetization Mr relative to saturated magnetization Ms of the magnetic thin film is equal to or greater than 0.78.