Cobalt modified iron oxides: dependence of surface topography on preparation method and resulting influence on magnetic properties

Depending on which method of synthesis is adopted for the deposition of a cobalt ferrite layer on gamma -Fe₂O₃ particles, very different surface topographies of the modified particles are observed in electron micrographs. The modifying layers are either grown as smooth epitaxially crystallized films or as a coating of more or less isolated ferrite particles. In the later case, significantly lower H_c-enhancements after modification are observed. The layer is still magnetically strongly interacting with the core particle of gamma -Fe₂O₃. To explain the results, differences in magnetostatic energy as a function of surface topography are discussed.