Wet process of preparing fine particles of ferrite of magnetoplumbite structure

Claim 1

A process of preparing fine particles of a ferrite having the magnetoplumbite structure, of the formula AO.sub.n (Fe.sub.2-(2x/6).sup.3+ M.sub.x/6.sup.2+ Sn.sub.x/6.sup.4+ O.sub.3) where A is Ba, Sr, and/or Pb, M is at least one of Fe, Cu, Zn, Co, Ni, Mn and Mg, n is between 4 and 6 and x is between 0.3 and 0.9 which comprises the steps of subjecting a powder of an iron oxide selected from the group consisting of γ-Fe 2 O 3 and (FeO) x ·Fe 2 O 3 , where 0<x≦1, and at least one compound of a divalent metal selected from the group consisting of chlorides, nitrates, and hydroxides of Ba, Sr and Pb to hydrothermal treatment at temperatures in the range from 80° to 360° C. in an aqueous alkali solution in the presence of an oxidizer, the atomic ratio of the total of Ba, Sr and Pb to Fe in the reaction system being in the range of from 1:8 to 1:12; and introducing tetravalent tin ions and at least one kind of divalent metal ions selected from the group consisting of Fe 2+ , Cu 2+ , Zn 2+ , Co 2+ , Ni 2+ , Mn 2+ , and Mg 2+ into the reaction system of the hydrothermal treatment such that the trivalent iron ions in the obtained ferrite having the magnetoplumbite structure are partly substituted by a combination of said divalent metal ions and tetravalent tin ions, the atomic ratio of Sn to Fe being in the range of 0.3:12 to 0.9:12 and the mole ratio of tetravalent tin ions to the total of said divalent metal ions in said reaction system being substantially 1:1.