The present invention relates to phosphorus-containing ferromagnetic pigments comprising, in particular, from 30 to 70% by volume of a core, said core comprising essentially iron and cobalt, and from 30 to 70% of a shell, said shell comprising essentially aluminum, phosporus, silicon, oxygen, and optionally magnesium and sodium; the invention further relates to a process for preparation of said pigments, their use in magnetic recording materials and magnetic recording materials which contain such pigments.