Preparation And Properties Of Pb（Zr,Ti）O₃ Film-on-CoFe₂O₄ Ceramic Magnetoeletric Composites

Multiferroic magnetoelectric（ME） materials not only exhibit ferroelectric or/and ferromagnetic ordering, but also some new coupling effects such as manetoelectric effect, and thus show significant potential applications in sensors, new magnetoelectric storage and capacitance-inductance intergration devices, etc. Among them, ME composites have been attracting considerable attention for their excellent ME effect at room temperature. The present work in this dissertation focuses on the fabrications of ME composites composed of the ferroelectric Pb（Zr,Ti）O₃（PZT） and the ferromagnetic CoFe₂O₄（CFO）, and the characterization of magnetic-field-induced polarization of the ME composite with different compositions and orientations.The Pb(Zr_xTi_1-x)O₃（x=0.2, 0.4, 0.52, 0.6 and 0.8） thin films were fabricated on the polished CFO ceramic substrate at low temperature by sol-gel method. This pseudo 2-2 type ME composite system can avoid the co-sintering distortions, diffusions or reactions at the interface of two phases during the conventional high temperature co-sintering. The ME properties of the different content PZT film/CFO ceramic system were characterized and show that: the ME composite displays obvious ME coupling effect, and its ME coupling coefficient(α_E31) dependence on the applied dc magnetic field is consistent with the CFO piezomagnetic coupling coefficient（dλ/dH） dependence on the applied dc magnetic field, demonstrating that the coupling mechanism between CFO and PZT phases is the strain（stress） mediated ‘magnetic-mechanical-electric’ coupling. The maximum value of room temperature in-plan ME coupling coefficient with x=0.2⁰.8 are 26.7,33.3,54.5,35.8 and 28.1 mV/cm·Oe, respectively. The PZT film with a Zr/Ti ratio close to morphotropic phase boundary（MPB） displays best properties. The introduction of PbO seed layer facilitates the [100] orientation of Pb(Zr_0.52Ti_0.48)O₃ films. The enhancement of [100] PZT and the reduction of [111] PZT not only improve piezoelectric property, but also largely enhance the ME coupling effect. The maximun ME coupling coefficient reaches up to 80.5 mV/cm·Oe in the PZT/PbO/CFO system, which is 1.8 times of that in PZT/CFO system.