US Patent 7144626 Magnetic iron oxide particles and magnetic toner using the same

There are provided magnetic iron oxide particles having an average particle diameter (Dp50) of primary particles of 0.05 to 0.3 μm, an average particle diameter (Da50) of secondary particles of 0.055 to 0.9 μm, and a ratio of the average particle diameter (Da50) of the secondary particles to the average particle diameter (Dp50) of the secondary particles (Da50/Dp50) of 1.1 to 3.0, as well as a magnetic toner containing the magnetic iron oxide particles. The magnetic iron oxide particles of the present invention are in the form of small agglomerated particles and exhibit an excellent dispersibility, and the magnetic toner using the magnetic iron oxide particles is excellent in electrification stability.