Abstract. Hexagonal Co-containing Z-; Y- and M-type ferrites are used as soft magnetic materials for multilayer inductors for operating frequencies up to 3 GHz. Co2Z-type Ba3Co2Fe24O41, iron excess Ba3Co2-yFe24+yO41 (0 y 0.8) and Ba3Co2-CuxFe24O41 (0 x 1.0) ferrites have their stability intervals between 1260-1350°C. The permeability of a ferrite with y = 0.6 sintered at 1300°C is µ = 30 throughout the MHz. Addition of Bi2O3 shifts the maximum shrinkage down to 950°C. Their permeability is µ = 5 because of partial decomposition of the Co2Z phase. Y-type ferrite Ba2Co1.2-xZnxCu0.8Fe12O22 (x = 1.2) sintered at 1100°C shows a permeability of µ = 20. Sintering at 900°C reduces the permeability to µ = 10. M-type BaCo1.2Ti1.2Fe9.6O19 ferrites sintered at 970°C display a permeability of µ = 35.