CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 40 (2014) 1933–1937 Effects of Mg doping on multiferroic properties of bilayered Co 1 À x Mg x Fe 2 O 4 /PMN–PT composite thin films J.M. Li a,b , G.Z. Li a , Z.H. Bai b , L.L. Wang c , M. Feng a,n , H.B. Li a,n a Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping 136000, PR China b School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, PR China c College of Science, Changchun University, Changchun 130022, PR China Received 7 July 2013; received in revised form 18 July 2013; accepted 18 July 2013 Available online 26 July 2013 Abstract Multiferroic Co 1 Àx Mg x Fe 2 O 4 /0.68Pb(Mg 1/3 Nb 2/3 )O 3 –0.32PbTiO 3 (CMFO/PMN–PT) bilayered thin films were prepared on Pt/Ti/SiO 2 /Si substrates by a simple sol–gel spin-coating technique. The effects of the Mg content on the electrical, magnetic, and magnetoelectric (ME) properties of the CMFO/PMN–PT bilayered thin films were investigated. It was found that increasing the Mg concentration could obviously improve the ME properties of the bilayered thin films. The results indicated the Mg doping provides an effective way to obtain the high ME response in the CFO/piezoelectric bilayered thin films. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sol–gel processes; B. Nanocomposites; C. Magnetic properties; Magnetoelectric coupling 1. Introduction Multiferroic materials have received considerable attention during the past decades due to their potential applications in multiple-state memories, actuators, sensors, microwave sys- tems, and spintronic devices [1–4]. These materials not only exhibit ferroelectric and magnetic orders, but also have a magnetoelectric (ME) coupling effect between the electric and magnetic polarizations, that is, a spontaneous electric polariza- tion induced by an external magnetic field or a magnetization induced by an applied electric field. In the single phase compounds, however, the electric polarization and magnetiza- tion interact weakly with each other or their ME response occurs at low temperatures for practical applications, which makes composite materials with combination of magnetic and ferroelectric phases become an alternate way to enhance the ME effect [5,6]. With much attention paid to composite multiferroic thin films in recent years due to that their phase composition and connectivity could be modified or controlled at the nanoscale, and the ME physical mechanism could be studied in nanoscale. As known that the ME response in multiferroic composite is facilitated by an elastic interaction between ferroelectric and ferromagnetic components via piezoelectric effect and magne- tostriction [3]. Thus, the high piezoelectric and magnetic sensitivities are essential to acquire a large ME signal. Cobalt ferrite CoFe 2 O 4 (CFO) is well known for its largest magnetos- triction in all the spinel ferrites along with a moderate value of saturation magnetization. However, the ME voltage coefficient was far smaller than the predicted value due to the poor ME coupling between the ferroelectric and CFO phase. This feature was attributed to the large magnetic anisotropy and coercivity of CFO which restricted the domain wall motion process [7]. Substitution of Mg for Co at the tetrahedral site in CFO was considered to reduce magnetic anisotropy and coercivity while the value of magnetostriction coefficients kept a constant [8,9]. The substitution of Mg for Co in CFO is a good choice for the magnetostrictive phase due to its higher magnetostrictive response. (1 À x)Pb(Mg 1/3 Nb 2/3 )O 3 À xPbTiO 3 (PMN–PT) with a larger piezoelectric response than Pb (Zr 0.52 Ti 0.48 )O 3 (PZT) has become a better candidate for the ferroelectric phase [10]. Accordingly, it is of considerable interest to investigate Co 1 Àx Mg x Fe 2 O 4 /0.68Pb(Mg 1/3 Nb 2/3 ) www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.07.101 n Corresponding authors. Tel.: +86 434 3292210; fax: +86 434 3292233. E-mail addresses: mingfeng@jlnu.edu.cn (M. Feng), lihaibo@jlnu.edu.cn (H.B. Li).