Synthesis And Properties Of Magnetoeletric Composites CoFe₂O₄/SrTiO₃

Magnetoeletric materials show ferromagnetism and ferroelectricity simultaneously. Due to rich physical mechanics in this field and underlying application,they attract abundant research. Magnetoeletric composite,which is usually composed with piezoelectrics/piezomagnetics or ferroelectrics/ piezomagnetics, is a focus in the research. In this paper, we use SrTiO₃,which show no piezoelectricity or ferroelectricity in any temperature,to compose with CoFe₂O₄. Induced by thermal residual stress and high electric field, SrTiO₃ is transformed to ferroelectricity. So the composite show magnetoelectric coupling effect.CoFe₂O₄/SrTiO₃(xCoFe₂O₄-(1-x)SrTiO₃ (x=0.1,0.2,0.3)) powder is synthesized by sol-gel method,and calcined without pressure in air. And the ceramics is sintered at 1100oC or 1150oC and quenched at 700oC,then it own strong thermal residual stress and small leakage. Follwed by high electric field induce,SrTiO₃ in the composite convert to ferroelectricity. The remnant polarization of 0.2CoFe₂O₄-0.8SrTiO₃ under 22.5kV/cm measure electric field is 0.0019μC/cm2. And the dielectric constant of the polarized sample is 43, just a sixth of the sample before polarization. The electric hysteresis loop measure and huge change in dielectric constant indicates the structure transition in SrTiO₃. The paper manifest this transition by XRD and Raman spectroscopy.The measurement of the xCoFe₂O₄-(1-x)SrTiO₃ ceramics'dielectric constant under different magnetic field strength(0T, 0.2T, 0.5T, 1T) show magneto -capacitive effect, which manifests magnetoelectric effect. The 0.2CoFe₂O₄ -0.8SrTiO₃ ceramics, which is sintered at 1100oC and and quenched at 700oC,show a 3.6% change of dielectric constant under 1T and 100KHz.