Abstract: An activated magnetite catalyst is formed of activated iron oxide or iron particles with solid crystal lattice, from which oxygen is partly removed. When the activated mgnetite catalyst is prepared, oxygen is partly removed from solid crystal lattice of particles of Fe.sub.3 O.sub.4, Fe.sub.3 O.sub.4+x obtained by partly or entirely oxidizing Fe.sub.3 O.sub.4 or gamma-Fe.sub.2 O.sub.3. The catalyst is useful to decompose gaseous oxides.

Abstract: A magnetic powder treated with a coating agent, wherein the surface of the magnetic powder is coated with an alternating copolymer comprising a polyoxyethylene allyl methyl diether and maleic anhydride. An aqueous coating material containing the magnetic powder and a magnetic recording medium prepared by use of the magnetic powder. The magnetic powder of the present invention has a good dispersibility. The aqueous coating material containing the magnetic powder allows for coating under a simple and safe environment. Also the magnetic recording medium prepared by the use of magnetic powder exhibits excellent magnetic characteristics.

Abstract: Disclosed is a method for forming a ferrite film comprising, flowing downward or spraying an aqueous oxidizing agent solution on a substrate in a deoxidized atmosphere and simultaneously supplying an aqueous deoxidized solution containing at least ferrous ions, to effect a ferrite crystallization reaction on the substrate. This ferrite film is used for magnetic recording media, photomagnetic recording media, magnetic heads, etc.

Abstract: Disclosed is a conjugate comprising a magnetic material and a physiologically active substance bound to each other through a polyethylene glycol derivative, and a conjugate comprising a magnetic material and a polyethylene glycol derivative bound to each other. According to the present invention, a bioreactor enabling application to or recovery of physiologically active substances under liquid state by utilizing the magnetic properties is provided.

Abstract: A process for forming a ferrite film, which is characterized in that in an aqueous solution containing at least ferrous ions as metal ions, ferrous hydroxide ions FeOH.sup.+, or FeOH.sup.+ and other metal hydroxide ions, are uniformly adsorbed on the surface of a solid by an interfacial reaction at an interfacial boundary between the solid and the aqueous solution; and the adsorbed FeOH.sup.+ is oxidized to FeOH.sup.2+, whereupon FeOH.sup.2+ and metal hydroxide ions in the aqueous solution undergo a ferrite crystallization reaction to precipitate a ferrite layer on the surface of the solid.