An electron microscope study of thin ferrite films prepared by the oxidation of high purity vacuum-evaporated metal thin films

The oxidation of thin films of nickel, cobalt, iron, NiFe₂ and CoFe₂ has been investigated between 200 and 1200° C. The oxidation products for the elemental metals differ from the oxidation products observed in previous work upon bulk material. The oxidation mechanism proposed for bulk material is in general still valid in the thin film situation. Above oxidation temperatures of approximately 850° C both NiFe₂ and CoFe₂ form the respective ferrites, although in the case of nickel ferrite, traces of the -Fe₂O₃ tetragonal superstructure can still be detected at oxidation temperatures of 1200° C. Films of nickel ferrite and cobalt ferrite upon single-crystal magnesium oxide substrates, produced by oxidation of vacuum-deposited NiFe₂ and CoFe₂ thin films, have been investigated by transmission and scanning electron microscopy. It has been found that (100) nickel ferrite prepared by this technique grows epitaxially upon (100) magnesium oxide.