Close-circuit domain quadruplets in BaTiO$_3$ nanorods embedded in SrTiO$_3$ film

摘要

Cylindrical BaTiO3 nanorods embedded in (100)-oriented SrTiO3 epitaxial filmin a brush-like configuration are investigated in the framework of theGinzburg-Landau-Devonshire model. It is shown that strain compatibility atBaTiO3/SrTiO3 interfaces keeps BaTiO3 nanorods in the rhombohedral phase evenat room temperature. Depolarization field at the BaTiO3/SrTiO3 interfaces isreduced by an emission of the 109-degree or 71-degree domain boundaries. Incase of nanorods of about 10-80 nm diameter, the ferroelectric domains arefound to form a quadruplet with a robust flux-closure arrangement of thein-plane components of the spontaneous polarization. The out-of-planecomponents of the polarization are either balanced or oriented up or down alongthe nanorod axis. Switching of the out-of-plane polarization with coercivefield of about $5.10^6$ V/m occurs as a collapse of a 71-degree cylindricaldomain boundary formed at the curved circumference surface of the nanorod. Theremnant domain quadruplet configuration is chiral, with the $C_4$ macroscopicsymmetry. More complex stable domain configurations with coexisting clockwiseand anticlockwise quadruplets contain interesting arrangement of stronglycurved 71-degree boundaries.