Influence of residual stress on magnetoelectric coupling of bilayered CoFe2O4/PMN–PT thin films

Multiferroic CoFe2O4/0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (CFO/PMN–PT) bilayered thin films with different CFO layer thicknesses were prepared on Pt/Ti/SiO2/Si substrates using the sol–gel technique. The bottom PMN–PT layer exhibited a highly (111) preferred orientation as conformed by a bidimensional (2D) planar X-ray diffractometer (XRD2). The influence of the thickness on the ferroelectric, dielectric, ferromagnetic, and magnetoelectric (ME) properties of the CFO/PMN–PT bilayered thin films was investigated. The residual stress of the top CFO layer films was characterized by means of grazing incidence X-ray diffraction. The ME signal is strongly dependent on the residual stress status of the CFO layer, which provides direct evidence for a stress-induced ME coupling mechanism in the multiferroic bilayered thin films. The maximal ME coupling coefficient of the bilayered thin films reaches up to about 65.2 mV cm−1Oe−1, which was higher than that reported previously.