Flux-Closure Domains in PbTiO3/SrTiO3 Multilayers Mediated without Tensile Strain

Ferroelectric flux-closure domains are promising for carrying information with ultrahigh-density capacities. Particularly, epitaxial tensile strains from external substrates are believed to be important for the formation of these flux-closure domains, but they may limit corresponding applications as high-density memory units. Herein, via pulsed laser deposition method, PbTiO3/SrTiO3 multilayered films are deposited on the cubic (001)-oriented SrTiO3 substrate, which is barely a misfit strain with a PbTiO3 film. The interaction between 90 degrees domains and insulation boundaries in PbTiO3 layers forms the three different flux-closure domains in the multilayered film structure without tensile strain. The complex flux-closure domain structure is investigated by advanced transmission electron microscopy, which is determined to be the width of the a1(1) and a1(2) domains, and the width of the a domains is subject to the thickness of the bottom PbTiO3 layer. Because the bottom PbTiO3 film thickness is proportional to the width and distance between the a1(1) and a1(2) domains, we can easily obtain various flux-closure domain configurations by varying the bottom and top PbTiO3 film thickness ratios. Furthermore, the creation of the flux-closure domain in PbTiO3 films is corroborated by the phenomenological theory. This finding allows us to manipulate domains in order to create and construct novel nanoscale ferroelectric devices with exotic properties.