| abstract |
The invention relates to needle-shaped, cobalt-modified iron oxides, consisting of a core of an iron oxide of the formula FeO x with values for X of 1.33 to 1.5 and one, based on the total amount of the material, a total of 0.4 to 12% by weight. % Of cobalt and up to 5% by weight of iron (II) ions containing ferrite shell, which are characterized in particular with regard to the coercive field strength by improved aging resistance, and a process for their preparation. |