Optical Control of Multiferroic Orderings
Yi-Chun Chen1*, Yi-De Liou1, Sheng-Zhu Ho1, Meng-Xun Xie1, Yi-Ting Hsieh1, Yu-Chen Liu1, Heng-Jui Liu2, Ying-Hao Chu3, Jan-Chi Yang1
1Department of Physics, National Cheng Kung University, Tainan, Taiwan
2Department of Materials Science and Engineering, National Chung Hsing University, Taichung, Taiwan
3Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan
* Presenter:Yi-Chun Chen, email:ycchen93@mail.ncku.edu.tw
Optical control of multiferroic properties has become an emerging research topic due to its advantages of non-contact characteristics, which has great potential in novel storage devices. However, what light provides is an alternating electromagnetic wave, so optical control seems to be unlikely to cause an ordering arrangement in a specific direction. In recent years, various interesting physical properties arising from manipulating strain-related energy terms in epitaxial films. In this study, we use local strain as a medium to achieve the optical control of multiferroic orderings. The strain distribution from local thermal expansion or phase change is induced by light, and through the manipulation of local strain distribution, a special multiferroic order can be obtained. Optical control were demonstrated in two complex oxide system, strained BiFeO3(BFO) and Pb(Zr0.2Ti0.8)O3 (PZT) epitaxial films. For strained BFO films, the stable phase transformed from rhombohedrally- to tetragonally- distorted monoclinic perovskite, which simulated the material system near the morphotropic phase boundary. A light driven flexoelectric effect allows the targeted nucleation of the ordered domains, which further enables macroscopic domain engineering. For tetragonal PZT films, the large piezoelectric response mainly originates from the switching of 90-degree c/a domains due to the strain-relief-induced reorientation. A special superdomain structure is found when the film is grown on the (110)-oriented SrTiO3 (STO). The in-plane strain from STO (110) breaks the uniaxial symmetry of the tetragonal PZT film, and with optical control of the strain energy, superdomains can be switched back to normal domains in local areas. This study provides a basic understanding of the influence of local stress on breaking multiferroic symmetry, and also gives another route to optical control of multiferroic orderings.

Keywords: multiferroics, optical control, scanning probe microscopy, ferroelectric domains