Phase Diagram of BiFeO 3 /LaFeO 3 Superlattices: Antiferroelectric-Like State Stability Arising from Strain Effects and Symmetry Mismatch at Heterointerfaces

Abstract : Artificial (BiFeO3)0.5Λ /(LaFeO3)0.5Λ superlattices (SLs) have been grown by pulsed laser deposition. The periodicity Λ was varied from 150 Å to 25 Å and the relative ratio between BFO and LFO is kept constant in each period. X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy investigations indicate antiferroelectric-like structures for large periodicity (Λ≥76 Å) while Pnma LaFeO3-like structures are observed for small periodicity Λ≤50 Å. Room temperature Magnetic measurements were obtained by vibrating sample magnetometry and suggest antiferromagnetic ordering with weak ferromagnetism. Temperature dependent x-ray diffraction studies show an important shift 2 of paraelectric-antiferroelectric phase transition scaling with BFO thickness. Strain and size effects explain this behavior and discussion is also made of the possible role of the oxygen octahedral rotation/tilt degree of freedom.