Preparation And Magnetoelectric Characteristics Of PZT5/NiFe₂O₄Magnetoelectric Composites

Magnetoelectric coupling effects (ME effects) is referred to the materials which could be electrically polarized in the magnetic fields or be magnetized in the electrical field, which is called as a ferroelectricity and ferromagnetism coupling effects. The materials which behave as the magnetoelectric coupling effects are called magnetoelectric materials which show high potential for technological applications. Compared to single phase system, magnetoelectric composites have much abundant properties. By now, there are many important research results which focused on the preparation of magnetoelectric composites and the ME effects. Based on the former work, we carried out the research with PZT5/NiFe2O4magnetoelectric composites, which mainly includes the following four parts:(1) PZT5and NiFe2O4were selected as the ferroelectric phase and ferromagnetic phase respectively. By traditional solid state sintering method, according to special mole ratios (x=0.1,0.2,0.1,0.2and0.5),0-3type (1-x)PZT5/xNiFe2O4magnetoelectric composites were prepared. XRD analysis showed that two phases in0-3composites were mixed mechanically, which made clearly that obvious chemical reactions in the sintering process did not take place. With the increase of ferromagnetic phase, peaks of NiFe2O4phase were more obvious. The dielectric spectra, electric hysteresis loops and magnetic hysteresis loops analysis showed that ferroelectric properties and dielectric properties of the composites increased with the increase of ferroelectric content, while the ferromagnetic properties decrease.(2) Through different magnetic fields and driving voltages,0-3type PZT5/NFO composites showed magneto-dielectric effects. Plus magnetic fields made capacitances and resistances bigger at low frequencies. The magnetoelectric effects came from the resistance increasing of NiFe2O4under magnetic fields. Whereas increasing driving voltage made resistances smaller at low frequencies with obscure changing of capacitance which was originated with the combined actions of the turning of electric dipoles on the surface of the composites and the oxygen vacancies.(3) According to the different thickness ratios (tPZT5:tNFO:tPZT5=0.5:1:0.5,1:1:1,1.5:1:1.5and2:1:2), sandwich structure PZT5/NiFe2O4/PZT5magnetoelectric composites (hereinafter referred to as P/N/P) were prepared. By electric hysteresis loops, magnetic hysteresis loops and dielectric spectra analysis, P/N/P composites with thickness ratio of2:1:2were found to have the best ferroelectric and ferromagnetic properties, which had the biggest saturation polarization (Ps) and remnant polarization (Pr) of2.36μC/cm2and1.47μC/cm2, respectively; saturation magnetization (Ms), remnant magnetization (Mr) and coercivity field (Hc) of6emu/g,1.4emu/g and95.7Oe, respectively.(4) By the analysis of dielectric spectra of the polarized sandwich structure P/N/P magnetoelectric composites, it was found that the applied electric fields and magnetic fields could regulate the resonant frequencies of the composites. By the constitutive equations of the piezoelectric and magnetostrictive materials, we got the relationships of the elastic modulus between the P/N/P magnetoelectric composites and the resonant frequencies. As a result, the resonant frequency regulation of applied magnetic fields was due to the elastic modulus change of NiFe2O4caused by the magnetic fields. The resonant frequency regulation of applied electric fields was due to the inverse piezoelectric effects of PZT5. The stress transmitted from PZT5to NiFe2O4, and then influenced the elastic modulus changing of NiFe2O4.