Layer engineering for the optimization of multiferroic properties in complex bismuth ferrite-based heterostructures grown on polycrystalline FTO

This study investigates the influence of stacking architecture on the film growth and multiferroic properties of BiFeO 3 -based heterostructures grown on fluorine-doped tin oxide (FTO) substrates. Using radio-frequency magnetron sputtering, two heterostructures combining Bi 0.85 Pr 0.15 Fe 0.97 Mn 0.03 O 3 (E) and Bi 0.60 Ba 0.25 Pr 0.15 Fe 0.945 Ni 0.025 Mn 0.03 O 3 (M) were deposited: a continuous bilayer, S1 (E180/M30), and a multilayer architecture, S2 [3(E60/M10)], while maintaining the same total deposition time of 210 min. Cross-sectional electron microscopy revealed architecture-dependent differences in film growth, with average thicknesses of 184.9 ± 9.2 nm for S1 and 113.4 ± 3.8 nm for S2. X-ray diffraction analysis indicated contributions from rhombohedral ( R3c ) and orthorhombic ( Pbam ) structures in both heterostructures. PFM measurements showed butterfly-like loops and phase changes close to 180° in both architectures, supporting a predominantly ferroelectric/electromechanical local response. S1 exhibited the larger electromechanical response, with a displacement variation of approximately 1.12 nm and a broader butterfly loop, whereas S2 maintained a well-defined response despite its lower thickness and multilayer configuration. In contrast, S2 exhibited a volume-normalized magnetization amplitude of 18.30 emu/cm 3 , substantially higher than that of S1 (3.92 emu/cm 3 ), although with lower coercivity (92.3 Oe compared with 295.8 Oe for S1). These findings highlight that, beyond chemical composition, layer engineering on low-cost polycrystalline substrates like FTO is a strategic route to tuning the functional balance between electromechanical and magnetic responses in thin-film heterostructures.