Agence Nationale De Valorisation De La Recherche (anvar)

Theophile Plante

Paul Hagenmuller

Gerard Demazeau

Michel Pouchard

Patrick Maestro

Process for making a novel ferromagnetic chromium dioxide and rhodium dioxide material in the form of a solid solution Cr.sub.1-x Rh.sub.x O.sub.2 where x is a number between 0 and 0.5. It essentially comprises oxidation, under suitable conditions of temperature and pressure, of hydrated or anhydrous Cr.sub.2 O.sub.3 or of a precursor of Cr.sub.2 O.sub.3, in the presence of (1) an appropriate amount of a compound of rhodium III able to give RhO.sub.2 under reaction conditions and (2) of an oxidizing agent consisting of an oxygenated compound free from metallic cations other than chromium and having, under the reaction conditions, a partial oxygen pressure at least equal to that corresponding, under the same conditions of temperature and pressure, to the equilibria Cr.sub.2 O.sub.3 +1/2O.sub.2 .revreaction.2CrO.sub.2 and Rh.sub.2 O.sub.3 +1/2O.sub.2 .revreaction.2RhO.sub.2 as well as eventually (3) of dilution water and/or of at least an additional doping agent acting as buffer in the reaction medium and/or a conventional modifying agent. The invention is useful for the manufacture of a ferromagnetic material possessing improved magnetic characteristics.

Novel ferromagnetic chromium dioxide and rhodium dioxide material and

Chromium dioxide CrO.sub.2 is prepared by oxidizing hydrated trivalent chromium oxide Cr.sub.2 O.sub.3, xH.sub.2 O, where x is at least 1, at a temperature of at least 350.degree. C and under pressures of at least 2 kilobars. The reaction is carried out in an oxidizing medium, which is a solid or an aqueous liquid solution, essentially constituted by a compound of the formula HXOy, zH.sub.2 O, wherein X represents an atom of chlorine or iodine, y is a positive integer less than or equal to 4, and z is a number which is a function of the dilution of said compound in the solution or a function of the crystallization water in the case of a solid oxidizing agent. The product is useful in any device requiring a compound which is ferromagnetic at a temperature less than 116.degree. C and notably in magnetic tapes.

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Pessac, France

Theophile Plante