Nanoscale PAPER Cite this: DOI: 10.1039/c8nr06041j Received 26th July 2018, Accepted 11th October 2018 DOI: 10.1039/c8nr06041j rsc.li/nanoscale Effect of substrate orientation on local magnetoelectric coupling in bi-layered multiferroic thin films† M. Naveed-Ul-Haq, * a Samira Webers,‡ b Harsh Trivedi, ‡ a Soma Salamon, b Heiko Wende, b Muhammad Usman, c Arif Mumtaz, d Vladimir V. Shvartsman a and Doru C. Lupascu a In this study we explore the prospect of strain-mediated magnetoelectric coupling in CoFe 2 O 4 –BaTiO 3 bi-layers as a function of different interfacial boundary conditions. Pulsed laser deposition fabricated thin films on Nb:SrTiO 3 (100) and Nb:SrTiO 3 (111) single crystal substrates were characterized in terms of their peculiarities related to the structure–property relationship. Despite the homogeneous phase formation in both films, transmission electron microscopy showed that the bi-layers on Nb:SrTiO 3 (100) exhibit a higher number of crystallographic defects when compared to the films on Nb:SrTiO 3 (111). This signifies an intrin- sic relationship of the defects and the substrate orientation. To analyze the consequences of these defects on the overall magnetoelectric coupling of the bi-layered films, piezoresponse force microscopy was performed in situ with an applied magnetic field. The local magnetic field dependence of the piezo- response was obtained using principal component analysis. A detailed analysis of this dependence led to a conclusion that the bi-layers on Nb:SrTiO 3 (111) exhibit better strain-transfer characteristics between the magnetic and the piezoelectric layer than those which were deposited on Nb:SrTiO 3 (100). These strain transfer characteristics correlate well with the interface quality and the defect concentration. This study suggests that in terms of overall magnetoelectric coupling, the Nb:SrTiO 3 (111) grown bi-layers are expected to outperform their Nb:SrTiO 3 (100) grown counterparts. Introduction Multiferroics are fascinating due to their ability to combine multiple ferroic orders such as ferroelectric, ferromagnetic, and ferroelastic in one phase or material system. These materials have attracted immense attention due to their most interesting property of coupling between different ferroic order parameters. 1 In particular, the magnetoelectric (ME) effect allows the control of polarization (magnetization) by an exter- nal magnetic (electric) field. There has been an enormous amount of research dedicated toward the understanding of the physics behind the ME coupling and the technological appli- cations of the ME effect. 1,2 Multiferroics can be divided into two broad categories, intrinsic ones where both magnetic and electric orders are intertwined in the same phase, and composites consisting of magnetic and dielectric phases connected in a certain con- figuration. In the latter, magnetoelectricity appears due to coupling at the interfaces. Single phase multiferroics show a low ME coupling usually only at cryogenic temperatures. 3 At the same time, composite multiferroics manifest ME coupling that is several orders of magnitude stronger, and do so at room temperature. Among the various coupling mechanisms, the most popular one is stress–strain transfer at the interface between a piezoelectric and a magnetostrictive phase. The direct magnetoelectric effect in multiferroic hetero- structures is valuable from a device perspective, because it permits transformation between a magnetic signal and an electric voltage without any source-currents or any need for cooling. Magnetic field sensors designed on the basis of the direct ME effect are expected to be compact and economical, 4 with high sensitivity 5–7 and a broad operational temperature bandwidth. 8 In multiferroic magnetoelectric composites inter- † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c8nr06041j ‡ These authors contributed equally to the article. a Institute for Materials Science and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitätsstraße 15, 45141 Essen, Germany. E-mail: naveed.ul-haq@uni-due.de b Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany c Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China d Department of Physics, Quaid-i-Azam University, Islamabad, Pakistan This journal is © The Royal Society of Chemistry 2018 Nanoscale Published on 11 October 2018. Downloaded by Universitaet Duisburg Essen on 11/2/2018 6:14:30 PM. View Article Online View Journal