CERAMICS Electric and magnetic properties of ferromagnetic/ piezoelectric bilayered composite Marin Cernea 1, *, Bogdan Stefan Vasile 2 , Vasile Adrian Surdu 2 , Roxana Trusca 2 , Cristina Bartha 1 , Floriana Craciun 3 , and Carmen Galassi 4 1 National Institute of Materials Physics, P.O. Box MG-7, 077125 Bucharest-Magurele, Romania 2 University Politehnica of Bucharest, 060042 Bucharest, Romania 3 Istituto di Struttura della Materia-CNR (ISM-CNR), Area di Ricerca di Tor Vergata, 00133 Rome, Italy 4 CNR-ISTEC, Institute of Science and Technology for Ceramics, Via Granarolo 64, 48018 Faenza, Italy Received: 3 May 2018 Accepted: 6 July 2018 Published online: 17 July 2018 Ó Springer Science+Business Media, LLC, part of Springer Nature 2018 ABSTRACT One of the most promising ways for the realization of multi-functional materials is the integration of oxides with different properties in artificial heterostructures. In this paper, a novel piezoelectric–ferromagnetic heterostructure consisting of 0.92Na 0.5 Bi 0.5 TiO 3 –0.08BaTiO 3 (abbreviated as BNT–BT 0.08 ) and CoFe 2 O 4 layers is fabricated on Si–Pt substrate, by sol–gel method coupled with spin-coating technique. The composite thin film shows only perovskite Bi 0.5 Na 0.5 TiO 3 -like rhombohedral phase and CoFe 2 O 4 cubic phase. The thickness of CoFe 2 O 4 and BNT–BT 0.08 layers is * 280 and * 400 nm, respectively. BNT–BT 0.08 /CoFe 2 O 4 heterostructure thin film shows a saturation magnetization of 0.11 emu/g at 5 K and 0.07 emu/g at 295 K, dielectric constant of 235 at 1 kHz and tunability of 70% at 1 kHz and an electric field E = 110 kV/cm. The results reveal that the investigated hybrid piezoelectric/ferromagnetic structure shows piezoelectric behavior, good ferroelectric and ferromagnetic properties. This bilayer com- posite can be used in miniature low-frequency magnetic sensor and piezoelec- tric sensor for biomedical domain. Introduction Electronic devices with novel functionalities and applications are currently being explored [1, 2]. Recent advances in thin-film growing techniques have enabled the synthesis of oxide heterostructures where their structural, magnetic and electric proper- ties can be controlled. The main reason for increased scientific and technological importance of the composite structures is the possibility to combine two or more materials with different properties into a single heterostructure having properties belonging to each component. There are several reports on the synthesis and characterization of composites thin films with multifunctionalities such as: ferroelectric– ferromagnetic composites (BiFeO 3 –CoFe 2 O 4 [3], nickel ferrite-PZT and manganite-PZT [4], CoFe 2 O 4 – BaTiO 3 [5]), ferromagnetic–piezoelectric oxide Address correspondence to E-mail: mcernea@infim.ro; marincernea@yahoo.com https://doi.org/10.1007/s10853-018-2673-x J Mater Sci (2018) 53:14160–14171 Ceramics