Three-dimensional heteroepitaxy in self-assembled BaTiO3–CoFe2O4 nanostructures

Abstract

Self-assembled ${\mathrm{BaTiO}}_3–{\mathrm{CoFe}}_2{\mathrm{O}}_4$ complex oxide nanostructures have been synthesized by pulsed laser deposition. A single ceramic target with a molar ratio of $0.62{\mathrm{BaTiO}}_3–0.38{\mathrm{CoFe}}_2{\mathrm{O}}_4$ was used. Spinel ${\mathrm{CoFe}}_2{\mathrm{O}}_4$ and perovskite ${\mathrm{BaTiO}}_3$ phases spontaneously separated during heteroepitaxial growth on a single-crystal ${\mathrm{SrTiO}}_3\left(001\right)$ substrate. The nanostructures are epitaxial in-plane as well as out-of-plane, with ${\mathrm{CoFe}}_2{\mathrm{O}}_4$ nanopillar arrays embedded in a ${\mathrm{BaTiO}}_3$ matrix. The ${\mathrm{CoFe}}_2{\mathrm{O}}_4$ nanopillars have uniform size and spacing and nearly circular cross section. As the substrate temperature increases from 750 to $950°\mathrm{C}$ , the average diameter of the pillars increases from $\sim 9$ to $\sim 70\mathrm{nm}$ .