Method for producing hexagonal ferrites

A method of forming hexagonal ferrite particles having a size below 0.3 .mu.m comprising

• dissolving soluble salts of the metal components of the ferrite in water,
• precipitating said components with a base,
• separating off and washing the precipitate,
• dispersing the washed precipitate in an aqueous solution of boric acid or borax,
• drying the resulting dispersion to form a solid material of agglomerated particles comprising a homogeneous mixture of the cations of the formula I
• M.sup.2+ [Fe.sub.(12-2x/3-py/3) (Me.sup.2+).sub.x (Ma.sup.p+).sub.y ].sub.m [(M.sup.2+).sub.z B].sub.n I
• where
• M=Ba, Sr, Pb
• Me=Co, Zn, Ni, Mn, Cu
• Ma=Ti, Zr, Hf, Ge, V, Nb, In
• p=3, 4, 5
• x=0-3
• y=0-3
• z=0.2-3
• m=0.7-1.5
• n=0.04-10
• and at least one anion comprising at least one thermally decomposable anion,
• sintering the solid material at from 400.degree. to 900.degree. C. to form said ferrite dispersed in a glassy borate matrix,
• dissolving the glassy matrix with a weak acid, and separating off the ferite particles.