| Multiferroic materials have drawn much research interest due to their rich new physics and their potential for applications as multifunctional devices. The research for this kind material mainly focused on the new material development, physical properties and the magnetoelectric coupling effect and the mechanism of multiferroic etc. In this dissertation, we will focus our work on the follow aspects:1. A new kind of lead-free multiferroic magnetoelectric composites xCoFe2O4-(1-x)[0.948(K0.5Na0.5)NbO3-0.052LiSbO3] ( xCFO/(1-x)(KNN-LS) )(x=0.15,0.3,0.4,0.5,0.65)were successfully prepared by incorporating the dispersed CoFe2O4 ferromagnetic nano particles into (K0.5Na0.5)NbO3-LiSbO3 ferroelectric micro matrix. They are 0-3 type two-phase particulate composites. The dependence of dielectric properties, DC magnetization, ME effect on CFO phase content was systemically studied. The results show that the dielectric constant decreases with increasing CFO phase content at higher frequencies while the loss tangent increase with it. As the ferrite content increases, both the d33 and resistivity of the composites decrease. The saturation magnetic moment (Ms) and remanent magnetization (Mr) increase almost linearly with the increase in ferrite content. The ME output increases initially with the increase in dc bias magnetic field and then decreases with the further increase in the field. A maximum magnetoelectric voltage coefficient of 15.01 mV·cm-1·Oe-1 was observed from the composites with 40 mol% CFO at 1kHz, which was a very high value in the nontoxic lead-free magnetoelectric composites system.2. Based on the above results, magnetoelectric ceramics 0.6(K0.5Na0.5)NbO3- LiSbO3, which has the maximum magnetoelectric voltage coefficient, was selected for study. Electric-field-induced and magnetic-field-induced effects are investigated in this ceramics at room temperature. The ceramics are found to exhibit an interesting dielectric response under the presence of a dc electric and magnetic bias field. High tunability (3.35%) of electric-field-induced dielectric response under the low dc electric field of 2 kV/cm and significant MD (3.99%) of magnetic-field-induced dielectric response were obtained at 7T. The ME effect are strongly dependent on the driving field frequency and the bias magnetic field (HBias). A large direct ME (DME) effect and converse ME (CME) effect are found in this 0-3-type structured multiferroic ceramic. Large CME coefficient in excess of 2.15×10-10 s/m is obtained at low frequency (1 kHz) and low magnetic bias field (2000 Oe).3. Nontoxic lead-free multiferroic magnetoelectric composites xNi0.98Co0.02Fe2O4/(1-x) [0.948(K0.5Na0.5)NbO3-0.052LiSbO3](xNCF-(1-x)KNN-LS) (x=0.15,0.3,0.4,0.5) were successfully prepared by incorporating the dispersed Ni0.98Co0.02Fe2O4 ferromagnetic nanoparticles into (K0.5Na0.5)NbO3-LiSbO3 ferroelectric micromatrix. The dependence of dielectric properties and DC magnetization on NCF phase content was systemically studied. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range, and the dielectric constant decreased with the increase in ferrite NCF content. The saturation magnetic moment (Ms) and remanent magnetization (Mr) increase almost linearly with the increase in ferrite content. The magnetoelectric (ME) coupling effects including direct ME (DME) effects and converse ME (CME) effects were investigated in detail at room temperature.The results show that the NCF content x significantly affects the ME output of the composites. The CME and DME behaviors are strongly dependent on the driving field frequency and the bias magnetic field (HBias). The maximum DME coefficient was observed to be 12.2mV·cm?1·Oe?1 at the low frequency of 1 kHz for the composite with 15 mol% NCF. Large CME coefficient in excess of 3.1×10-10 s/m is obtained at low frequency and low magnetic bias field, which was a very high value in the nontoxic lead-free magnetoelectric ceramics system.4. Multiferroic magnetoelectric film KNN-CFO-KNN is firstly prepared on c-axis texture NiW metallic tape by means of pulsed laser deposition (PLD). The dielectric properties, DC magnetization, ME effect were systemically studied. The low loss tangent is obtained and the ferroelectric properties is improved. The relative dielectric constant changes dramatically with dc bias electric field. At 20 kHz, high tunability (2.1%) and FOM (89.8) of electric-field-induced dielectric response are obtained under the low voltage of 0.8V. The frequency-dependent ME effect shows that there two peaks at the frequency of 800 Hz and 48 kHz.The maximum ME outputαDME in excess of 1013.9 mV? cm-1?Oe-1 is obtained at frequency 0f 48 kHz. The value is much bigger than that of particulate multiferroic composites.5. The orthorhombic Dy0.9Ni0.1MnO3 films are fabricated on the surface of SrTiO3(110)with the method of pulsed laser deposition (PLD). The ferroelectric properties, magnetization and Electric-field-induced and magnetic-field-induced dielectric response were studied. The film show ferroelectricity at room temperature and the remanent polarization is 0.49μC/cm2. The magnetic field dependence of the magnetization showed a clear hysteresis at low temperature. The sample is found to exhibit dielectric response under the presence of a dc electric and magnetic bias field. High tunability (6.4%) of electric-field-induced dielectric response is obtained at 200 kHz and significant MD (46.4%) of magnetic-field-induced dielectric response is obtained at a higher temperature of 225K and magnetic field of 5T.
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