BaTiO 3 –CoFe 2 O 4 –BaTiO 3 trilayer composite thin films prepared by chemical solution deposition (original) (raw)

We investigated in this paper a novel bilayer composite obtained by sol-gel and spin coating of the ferroelectric 0.92Na 0.5 Bi 0.5 TiO 3-0.08BaTiO 3 (abbreviated as BNT-BT 0.08) and ferromagnetic CoFe 2 O 4 phases, for miniature low-frequency magnetic sensors and piezoelectric sensors. This heterostructure, deposited on Si-Pt substrate (Si-Pt/CoFe 2 O 4 /BNT-BT 0.08), was characterized using selected method such as: X-ray diffraction, dielectric spectroscopy, piezoelectric force microscopy, SQUID magnetometry, atomic force microscopy/magnetic force microscopy, and advanced methods of transmission electron microscopy. CoFe 2 O 4 /BNT-BT 0.08 ferromagnetic-piezoelectric thin films show good magnetization, dielectric constant and piezoelectric response. The results of analyses and measurements reveal that this heterostructure can have applications in high-performance magnetoelectric devices at room temperature. In recent years, the manufacture of composite materials from components with different macroscopic properties was studied extensively 1-5. These composites have applications in electronic devices with novel distinct functionalities 6-8. Oxide heterostructure thin films with electric and magnetic properties were prepared by various techniques, such as: sol-gel 9 , pulsed laser deposition 10 , rf sputtering 11 , tape-casting method 12 , etc. There are several reports on composites with electrical, ferroelectric and ferromagnetic behaviors, for example: ferroelectric-ferromagnetic composites (BiFeO 3-CoFe 2 O 4 13 , nickel ferrite-PZT and manganite-PZT 8 , CoFe 2 O 4-BaTiO 3 14) and ferromagnetic-piezoelectric oxide heterostructures (La 0.7 Sr 0.3 MnO 3-PbZr 0.2 Ti 0.8 O 3 15 , CoFe 2 O 4-PZT 10). There are few reports on lead free ferroelectric (Na 0.5 Bi 0.5 TiO 3)-magnetostrictive (CoFe 2 O 4) particulate composites 16-19 but bilayer ferrite-piezoelectric composites of CoFe 2 O 4 and BNT-BT 0.08 have not been reported so far a heterostructure composed of a piezoelectric and a magnetic one. In this work we have created a heterostructure thin film composed from piezoelectric and magnetic materials. We have investigated the composite thin film Si-Pt/CoFe 2 O 4 /BNT-BT 0.08 in which BNT-BT 0.08 and cobalt ferrite (CoFe 2 O 4) films were deposited in two subsequent steps on Si-Pt buffer, by sol-gel and spin-coating techniques. Cobalt ferrite was chosen because is an important component for multiferroic heterostructure thin films or composites due to its high coercivity, moderate magnetization and highest magnetostriction coefficient 20. (Bi 0.5 Na 0.5)TiO 3 (BNT) doped with BaTiO 3 (BT) is selected as ferroelectric layer because BNT-BT 0.08 is considered a good candidate to replace the lead-based piezoelectric materials 21,22. It has been shown previously that the (1-x)BNT-xBT (BNT-BT x) solid solution has in the compositional domain x = 0.06-0.10 a nearly morphotropic phase boundary (MPB) 23,24 where rhombohedral Bi 0.5 Na 0.5 TiO 3 and tetragonal BaTiO 3 phases coexist. Compared