Epitaxial pillar-matrix nanocomposite thin films of Bi-Ti-Fe-O and CoFe_2O_4 grown on SrTiO_3 (110)

摘要

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 CoFe_2O_4 (CFO) and (1110) oriented Bi_5Ti_3FeO_(15) (BTFO15) grown on SrTiO_3 (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 Bi_4Ti_3O_(12) • nBiFeO_3 (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 it’s 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.