Self-assembled multiferroic epitaxial BiFeO3–CoFe2O4 nanocomposite thin films grown by RF magnetron sputtering

Abstract

Self-assembled nanocomposites consisting of ferrimagnetic CoFe₂O₄ and ferroelectric BiFeO₃ were grown on Nb-doped SrTiO₃ (001) or SrTiO₃-buffered Si (001) substrates using radio frequency magnetron sputtering. Spinel CoFe₂O₄ formed as epitaxial pillars within a perovskite BiFeO₃ matrix, similar to nanocomposites grown by pulsed laser deposition. CoFe₂O₄ and BiFeO₃ grew with a cube-on-cube epitaxy on Nb-doped SrTiO₃, with partial relaxation of the in-plane strain of BiFeO₃. The sputter-grown nanocomposites showed an out-of-plane magnetic easy axis as a result of both the shape anisotropy of the pillars and the magnetoelastic anisotropy of CoFe₂O₄, but the latter was dominant. The BiFeO₃ matrix exhibited ferroelectric domains, and the removal of BiFeO₃ led to the reduction of magnetic anisotropy by the strain relaxation of CoFe₂O₄. For potential application in devices, the nanocomposites were integrated on buffered silicon substrates. Templating of the CoFe₂O₄ nanopillars was achieved by substrate patterning. These techniques facilitate the incorporation of multiferroic nanocomposites into memory and other devices.