Growth mechanism and magnetism of CoFe2O4 thin films; Role of the substrate

• CoFe2O4 films show epitaxial growth despite a large variation in lattice matching with substrates.
• The relaxed films only show strain under the critical thickness close to the interface when presence.
• Films are relaxed by epitaxial islands formation and growth defects with increasing thickness.
• Epitaxial CoFe2O4 shows different growth mechanisms and large variation of magnetic properties.

In bulk composite materials, interfaces between adjacent materials can be neglected when evaluating the individual functional properties on the macroscopic scale. However, in nanostructured materials, what is described as an interfacial region can be a significant amount of the total volume of the composite. These interfaces are difficult to analyse by conventional TEM and XRD. Here we describe how a combination of material and property analyses provides evidence of microstructural arrangement on apparently epitaxial film interfaces on different substrates. CoFe2O4 films were grown on SrTiO3, LaAlO3, BaTiO3 and MgO single crystal substrates, all cut in 0 0 1 direction. Our analyses explain the importance of chemical stability of the interface, crystallographic matching between the magnetic film and the dielectric growth template and the different growth mechanisms. The microstructural features in films with thicknesses between 13 and 100 nm were identified. The large variation in the magnetic properties of the films demonstrates the importance of the interfacial chemistry on the final functional properties.