Critical Limitations in the Fabrication of Biferroic BiFeO₃−CoFe₂O₄ Columnar Nanocomposites Due to Bismuth Loss

Abstract

The influence of the temperature during self-assembled growth of BiFeO3−CoFe2O4 columnar nanocomposites on (001) and (111) oriented SrTiO3 substrates has been investigated aiming to control pillar size and lateral ordering. The dramatic influence of the growth temperature on the nanoobject morphology is found to be basically due to the strong monotonic reduction in the bismuth content as the deposition temperature increases. There is a very narrow (tens of degrees) optimal window of substrate temperature, in which BiFeO3 could permit a small deficit of Bi without decomposition. The enhanced ferromagnetic response of samples deposited at higher temperature signals formation of secondary ferromagnetic phases caused by BiFeO3 decomposition. Therefore, the deposition temperature is not a suitable free parameter to control the nanoobjects topology in BiFeO3 nanocomposites.

On the strain coupling across vertical interfaces of switchable BiFeO3–CoFe2O4 multiferroic nanostructures

“…8 In the case of CFO-BFO nanostructures, the only system where the reversal of magnetization by electric field at room temperature has been demonstrated, 2 only out-ofplane unit cell parameter values are reported. 9,10 In contrast, a detailed study of lattice strains was reported for BFO-Sm 2 O 3 columnar nanocomposite heteroepitaxial films on SrTiO 3 ͑001͒ ͑STO͒, 11 showed that the vertical strain of both phases was determined by the mechanical interaction between BFO and Sm 2 O 3 , rather than by the stress caused by the substrate.We have measured all strains in CFO-BFO nanostructures. CFO is in-plane relaxed but out-of-plane strained, with semicoherent CFO-BFO interfaces.…”

“…Nanocomposites with thickness in the 100-200 nm range were deposited at a rate of around 0.9 Å/s on STO substrates at temperatures in the 625-675°C range by pulsed laser deposition ͑KrF laser, 5 Hz͒ using a BFO-CFO target with molar ratio of 65:35. 10 The lattice strain was analyzed by x-ray diffractometry ͑XRD͒ with Cu K␣ radiation and by HRTEM. Some samples were etched with HCl ͑10%, 75 s͒ to selectively remove the BFO phase.…”

Long-range order of Ni2+ and Mn4+ and ferromagnetism in multiferroic (Bi0.9La0.1)2NiMnO6 thin films

“…Magnetic properties are not solely determined by the B-site order but also by the precise stoichiometry and valence state of the existing species. This is particularly relevant as the highly volatile bismuth 15 may lead to cationic defects that, in turn, may modify the electronic configuration of Ni/Mn ions or the oxygen contents.…”

In-plane strain control of the magnetic remanence and cation-charge redistribution inCoFe2O4thin film grown on a piezoelectric substrate

“…1,6 The rareness of room-temperature multiferroics 2 has then led many workers to combine ferroelectric materials with ferromagnetic phases at microscopic or nanoscopic scales, for examples, nanoparticulate composite films, [11][12][13][14] multilayered thin films, 15 and nanopillar or columnar film structures. [16][17][18][19] In these dissimilar two-phase systems, magnetoelectric ͑ME͒ coupling effects can be considered as arising from the interfacial strain-mediated coupling of piezoelectricity and magnetostriction.…”

“…20 Moreover, the processing of nanopillar or columnar structure is not simple, in general, to be readily adapted to a wide variety of multiferroic composites. 19 Here we propose a multiferroic bilayer structure in which the magnetic response is controlled by the in-plane compressive strain of the top-layer epitaxially constrained by the bottom piezoelectric substrate. Figure 1 schematically depicts a ferromagnetic-piezoelectric asymmetric bilayer structure in which a single-crystalline 0.72Pb͑Mg 1/3 Nb 2/3 ͒O 3 FIG.…”