Epitaxial pillar–matrix nanocomposite thin films of Bi–Ti–Fe–O and CoFe2O4 grown on SrTiO3 (110)

Abstract

Controlling nanostructures and crystallographic orientations in epitaxial nanocomposite thin films are important for tuning their physical properties. Here, we present epitaxial nanocomposite thin films of (110) oriented CoFe2O4 (CFO) and (1110) oriented Bi5Ti3FeO15 (BTFO15) grown on SrTiO3 (110) substrates with a vertically aligned pillar–matrix type structure. The size and density of CFO pillars embedded in the BTFO matrix were controlled by the growth temperature and CFO concentration. Moreover, BTFO takes intergrowth phases with the general formula of Bi4Ti3O12 • nBiFeO3 (n = 1–∼1.5) depending on the growth temperature. Scanning probe analysis on the ferroelectric properties of BTFO15–CFO nanocomposite thin films suggested that the BTFO has a switchable out-of-plane polarization component originating from the tilted orientation of its a–b plane polarization. For high CFO pillar density, however, a non-negligible number of conductive paths which might be formed at the pillar–matrix interface are likely to prevent the polarization reversal.