Microstructure of the potentially multiferroic Fe/BaTiO₃ epitaxial interface

Abstract

The Fe/BaTiO₃ thin-film layered structure is a prototype of charge-mediated composite multiferroics, which is a promising but challenging route to achieve a sizable magnetoelectric effect. The real structure of the interface between the ferromagnetic Fe and ferroelectric BaTiO₃ layers is crucial. In this paper, epitaxial Fe layers were successfully grown on top of BaTiO₃ layers by carefully controlling the pulsed laser deposition and magnetron sputtering procedures. A detailed study of interfacial structure and defects at the Fe/BaTiO₃ interface was carried out by transmission electron microscopy (TEM). Electron diffraction patterns and diffraction contrast images reveal a definite epitaxial relationship between Fe and BaTiO₃ (001) films and a semi-coherent interface with nearly periodic interfacial dislocations. Based on high-resolution TEM images from both [010] and [110] direction observations, the interfacial dislocations were found to be partial with Burgers vectors and line directions of ⟨010⟩. By employing high-resolution Z-contrast imaging, the positions of individual atoms columns were resolved. The formation mechanism of interfacial dislocations was proposed in terms of geometrical models of the interface structure. On the basis of the remaining strain analysis in each layer, the effects of both BaTiO₃ thickness and the SrTiO₃ substrates on the density of the interface defects were discussed.

Keywords:

• multilayer thin films
• epitaxial growth
• interface structure
• high-resolution electron microscopy
• composite multiferroics

Acknowledgements

This work was supported by the National Basic Research Program of China (2009CB623705 and 2010CB631206), and the National Natural Science Foundation of China (No. 50871115 and No. 51171190).