Thin films of orthorhombic TbMnO3, as well as other orthorhombic manganites, epitaxially grown on cubic SrTiO3 substrates display an induced magnetic moment that is absent in the bulk (antiferromagnetic) counterpart. Here we show that there is a clea
r correlation between the domain microstructure and the induced magnetic moment in TbMnO3 films on SrTiO3. In addition, the distinct dependence of the magnetization with the film thickness is not consistent with domain magnetism and indicates that the domain walls, rather than the domains, are the origin of the net magnetic moment. Since the orientation of the domain walls can be designed by the film-substrate relationship and its density can be tuned with the film thickness, these results represent a significant step forward towards the design of devices based on domain wall functionality.
TbMnO$_{3}$ films have been grown under compressive strain on (001)-oriented SrTiO$_{3}$ crystals. They have an orthorhombic structure and display the (001) orientation. With increasing thickness, the structure evolves from a more symmetric (tetragon
al) to a less symmetric (bulk-like orthorhombic) structure, while keeping constant the in-plane compression thereby leaving the out-of-plane lattice spacing unchanged. The domain microstructure of the films is also revealed, showing an increasing number of orthorhombic domains as the thickness is decreased: we directly observe ferroelastic domains as narrow as 4nm. The high density of domain walls may explain the induced ferromagnetism observed in the films, while both the decreased anisotropy and the small size of the domains could account for the absence of a ferroelectric spin spiral phase.
