Preparation of stabilized acicular ferromagnetic chromium dioxide

In a process for the preparation of stabilized acicular ferromagnetic chromium dioxide particles by reaction of oxides of trivalent and hexavalent chromium at from 200.degree. to 600.degree. C. in a high pressure reactor under from 100 to 700 bar in the presence of water with the addition of at least one modifier based on antimony, selenium, tellurium and/or iron or their compounds and subsequent reductive treatment of the surface of the resulting chromium dioxide in an aqueous suspension with the formation of a compound of trivalent chromium on the surface, the improvement which comprises:

• absorbing from 0.1 to 5.0% by weight, based on the amount of chromium dioxide, of a hydroxycarboxylic acid of 2 to 6 carbon atoms onto the surface of the chromium dioxide particles subsequent to the reductive treatment of the particles.