| Ferromagnetic materials, ferroelectric materials, ferroelastic materials and multiferroic materials, which have several ferroic properties at the same phase, are all belonged to ferroic materials. This is a kind of important advanced functional materials. In this article, ferroic materials are choosed as the study object. Firstly, Ferroelectric materials, ferromagnetic materials and multiferroic materials were introduced, respectively, the main type of magnetoelectric composites and research progress of magnetoelectric composite thin films were discussed. Then, preparation and properties characterization method of ferroelectric thin films and multiferroic magnetoelectric composite thin films were introduced. The major reaseach content and experiment results can be summarised as follows:1. Polarization fatigue behaviors in Bi3.5Nd0.5Ti3O12ferroelectric thin filmsThe evolution of the fatigue behaviors in Bi3.5Nd0.5Ti3O12(BNT) ferroelectric thin films deposited on Pt(111)/Ti/SiO2/Si(100) substrates by chemical solution deposition (CSD) method effected by amplitude, frequency and profile of the driving electric field were reported. It is found that the switching with lower frequency and higher amplitude of the external voltages resulted in higher fatigue rates and only bipolar waveform type voltage can result in fatigue, whereas a unipolar voltage cannot. An empirical function with N/f is proposed in the frequency-dependence of polarization fatigue, where N is the number of switching cycles and f is the frequency of driving. It is indicated that injected charges from electrodes into films, the trapped charges, and suppression of the seeds of opposite domain nucleation are the main mechanism of fatigue in ferroelectric BNT thin films.2. Influence of pyrolysis temperature on ferroelectric properties ofLa and Mn co-doped BiFeO3thin filmsBi0.9La0.1Fe0.95Mn0.05O3(BLFMO) ferroelectric thin films were fabricated on Pt/Ti/SiO2/Si/substrates by the sol-gelprocess at different pyrolysis temperatures. The mass loss of BLFMO powder was investigated by thermo gravimetry analyser (TGA), and the polycrystalline structure and smooth surface of BLFMO thin films were characterized by X-ray diffraction (XRD) and atomicforce microscopy (AFM), respectively. The remnant polarization (Pr) of the BLFMO films pyrolyzed at420°C is21.2μC/cm2at thecoercive field (Ec) of99kV/cm and the leakage current density is7.1×10-3A/cm2, which indicates that the BLFMO thin filmsdisplay relatively good ferroelectric property at this temperature.3. Fabrication and magnetoelectric properies characterization of La0.6Ca0.4MnO3-Bi3.4Nd0.6Ti3O12composite thin filmsMagnetoelectric (ME) xLa0.6Ca0.4MnO3-(1-x)Bi3.4Nd0.6Ti3O12composite thin films with x=0.3,0.4, and0.5were fabricated on Pt/Ti/SiO2/Si(100) substrates by a chemical solution deposition method. The well-defined ferroelectric loops are observed. The Pr values are11.2,12.8, and13.9μC/cm2under the condition of about350kV/cm electric field for the composite films with x=0.3,0.4, and0.5. The composite films exhibit typical magnetic hysteresis loops, as well as remnant magnetizations. ME effect which is dependent on Hbias is observed. The results show that the films exhibit both good ferroelectric and magnetic properties, as well as a ME effect.4. Deposition sequence effect on magnetoelectric Bi3.25Nd0.75Ti3O12-La0.6Ca0.4MnO3composite thin filmsMagnetoelectric (ME) Bi3.25Nd0.75Ti3O12-La0.6Ca0.4MnO3(BNT-LCMO) composite thin films were deposited on Pt/Ti/SiO2/Si(100) substrates by a simple SOL-GEL method and spin-coating process with two different deposition sequences: BNT/LCMO/Pt/Ti/SiO2/Si (BLP) and LCMO/BNT/Pt/Ti/SiO2/Si(LBP). Our results show the composite thin films exhibit both good ferroelectric and magnetic properties, as well as a ME effect. BLP thin films have larger maximum ME voltage coefficient values than LBP structured thin films. The deposition sequence has a notable effect on the ferroelectric and magnetic properties and ME coupling behavior of the bi-layer thin films.5. Fabrication and properies characterization of magnetoelectric (Bi, La)4Ti3O12-CoFe2O4composite thin filmsMagnetoelectric xBi3.25La0.75Ti3O12-(1-x)CoFe2O4composite thin films with x=0.5,0.6, and0.7were deposited on Pt/Ti/SiO2/Si(100) substrates by a simple SOL-GEL method and spin-coating process. Well-defined ferroelectric loops are observed. The Pr values of the composite films with x=0.5,0.6, and 0.7are8.89,11.97, and13.78μC/cm2respectively, under about350kV/cm electric field. The composite films exhibit typical magnetic hysteresis loops, as well as remnant magnetizations. Magnetoelectric effect which is dependent on Hbias is observed. The composite films exhibit both good ferroelectric and magnetic properties at room temperature, as well as a magnetoelectric effect. |
PDF Full Text Request