Multiferroic behaviour of epitaxial NiFe₂O₄--BaTiO₃ heterostructures

Multiferroic NiFe₂O₄--BaTiO₃ (BTO) bilayered thin films are epitaxially grown on (001) Nb-doped SrTiO_3 (STO) substrates by pulsed-laser deposition (PLD). Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with (001)-orientation, i.e. (001)-NFO/(001)-BTO/substrate and (001)-BTO/(001)-NFO/substrate. Microstructure studies from x-ray diffraction (XRD) and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious magnetoelectric (ME) effect on coupling response.