Structural and multiferroic properties of epitaxial γ-Fe₂O₃–BiFeO₃/Bi_3.25La_0.75Ti₃O₁₂composite bi-layers

Abstract

Multiferroic properties of γ-Fe 2 O 3-BiFeO 3 /Bi 3.25 La 0.75 Ti 3 O 12 epitaxial composite bi-layers grown on SrRuO 3 /SrTiO 3 (1 1 1) are compared with the properties of single phase BiFeO 3 and Bi 3.25 La 0.75 Ti 3 O 12 thin films. The composite bi-layers show well-saturated hysteresis loops with a low coercive field, a high fatigue resistance and high saturation magnetization. The insulating Bi 3.25 La 0.75 Ti 3 O 12 underlayer reduces significantly both the leakage current and the coercive field of the heterostructure (200 kV cm −1) at the expense of a lower polarization (20 µC cm −2), while the epitaxial γ-Fe 2 O 3 secondary phase that develops within the relaxed epitaxial BiFeO 3 matrix allowed for a high saturation magnetization.

Piezoresponse force microscopy and magnetic force microscopy characterization of γ-Fe2O3–BiFeO3 nanocomposite/Bi3.25La0.75Ti3O12 multiferroic bilayers

“…Excellent macroscopic ferroelectric properties in terms of polarization hysteresis have been obtained [7] and were confirmed at the nanoscale by PFM measurements (Fig. 2) which showed regions exhibiting a strong PFM contrast, surrounded by regions without a response.…”

“…The detailed deposition parameters as well as the structural and ferroelectric properties at the macroscopic scale have been reported earlier [7]. The thicknesses of both g-Fe 2 O 3 -BiFeO 3 and Bi 3.25 La 0.75 Ti 3 O 12 layers were about 200 nm.…”

“…Further, the measured value of saturation magnetization M s is lower than the bulk value of the g-Fe 2 O 3 ($420 emu cm À3 [12]). Since all phases are epitaxial within the heterostructure [7], we partially ascribe this to elastic constraints exerted on the magnetic phase (g- Surprisingly, the observed in-plane and out-of-plane magnetic behaviors of these films are significantly different in terms of the value of their saturation magnetization. There are two possible scenarios which may affect the observed value of the magnetization saturation in our films.…”

“…[7], we compare the in-plane and out-of-plane macroscopic hysteresis loops of the g-Fe 2 O 3 -BiFeO 3 composite layer. As shown in Fig.…”

“…By choosing a Bi 3.25 La 0.75 Ti 3 O 12 (BLT) epitaxial insulating buffer layer, we have enhanced the various ferroelectric properties, such as resistance to ferroelectric fatigue and reduction of the ferroelectric coercivity of BFO-based nanocomposite thin film heterostructures [7]. Furthermore, we have also increased the value of the saturation magnetization of our films by controlling the concentration of magnetic g-Fe 2 O 3 in the BFO matrix.…”