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Nanostructured strain-coupled multiferroic composite thin films, combining magnetostrictive and piezoelectric phases, have attracted wide interest due to their strong magnetoelectric (ME) effect. Their stress-mediated coupling arises from the interfacial mechanical interaction between the two phases, which links their elastic, electric and magnetic fields and enables the mutual detection and control of magnetic and electric signals. Single-phase magnetoelectrics remain impractical for most devices, as their ordering temperatures lie below room temperature, whereas composite systems offer larger ME responses and a far wider choice of active phases. Applications span information storage, actuators, antennas and lower power electronics, and, importantly, magnetic field sensing. However, the dynamical magnetic-electric properties of nanoscopic bilayer systems and their application in magnetic field sensing remains poorly explored.
Pulsed laser deposition allows epitaxial oxide heterostructures to be grown with nanometric thickness control and was used in this work to prepare lead-free bilayer nanocomposite films combining BCZT ((1−x)(Ba0.7Ca0.3)TiO3–x[Ba(Zr0.2Ti0.8)O3]) and CoFe2O4 on SrTiO3 (100) substrates. BCZT is a ferroelectric with a piezoelectric coefficient reaching 496 pC/N in bulk ceramic samples, comparable to state-of-the-art PZT ceramics, while CoFe2O4 is an inverse spinel ferrite with high magnetostriction and magnetocrystalline anisotropy, making them good
candidates for strain-mediated ME coupling. Both stacking orders were grown, with either the ferroelectric or the ferrite deposited first, so that the influence of the growth sequence on the interface could be isolated.
The structural, morphological, dielectric and ferroelectric properties of the bilayers were characterized. X-ray diffraction shows that BCZT grows epitaxially on SrTiO3 but becomes polycrystalline when deposited onto CoFe2O4. The two stacking orders sustain interfacial strain of opposite sign, tensile when BCZT is grown onto the STO substrate and compressive when deposited on CFO respectively. Impedance spectroscopy resolves two thermally activated relaxation processes together with a pronounced thermal hysteresis, while P–E measurements confirm the polar responses. Electrical behaviour depends strongly on the stacking order. The films with BCZT deposited first show much higher capacitanceand well defined P-Hysteresis loops, as compared to the reverse configuration. This points to an important role of interfacial strain engineering in controlling the electrostatic boundary conditions in the multiferroic thin films.
| Which topic best fits your talk? | Condensed Matter Physics and Nanomaterials |
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| Affiliations | University of Minho |