PROCESS OF MAKING THIN FERROMAGNETIC FILMS AND ELECTROLYTE THEREFOR

1,199,421. Electrolytic deposition of ferromagnetic layers. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Nov. 24, 1967 [Nov. 26, 1966], No.53596/67. Heading C7B. Thin ferromagnetic layers of ferro nickel alloy are electrolytically deposited from a bath containing a selenuim compound in addition to iron and nickel salts, the pH of the bath being maintained below 3. The selenium is preferably present in quadrivalent form, e.g. as selenium dioxide, selenous acid or sodium selenite. During deposition the surface upon which the layer is to be deposited may be exposed to a powerful homogeneous magnetic field, the lines of force extending parallel to said surface. Either the workpiece potential or the current density at the workpiece is preferably held constant, at least in stages. In the example given the bath contained nickel sulphate, ammonium ferrous sulphate, boric acid, sodium chloride, saccharine, sodium lauryl sulphate and sodium selenate, the anode was formed of platinum, nickel or nickel and iron, and the cathode upon which the film was deposited was formed by a glass wafer upon which first chromium and then gold had been vapour deposited. Alternatively the substrate may be produced by sensitizing a glass plate in a solution of tin chloride, followed by activation in a solution of palladium chloride, electroless deposition of copper, electrolytic deposition of copper and coating with a glass fibre laminated epoxy resin foil. The resulting foil was removed from the glass and the surface which had faced the glass was coated with gold, electrolytically or electrolessly, which surface then formed the deposition surface for the ferromagnetic alloy film. Polished metals or chemically or electrolytically coated plastics or glasses may be used as the substrate.