Preparation And Characterization Of The Multiferrotic YMnO₃

Multiferroic materials,which show simultaneous ferroelectric and magnetic ordering,exhibit unusual physical properties.Multiferroics have high potential in opening a new field of innovative devices.The preparation and physical properties of Rare-earth manganese oxides thin film have attracted much attention in recent years.Hexagonal yttrium manganese oxide (YMnO₃),which exhibit simultaneously ferroelectric and antiferromagnetic properties, was proposed as a candidate material for nonvolatile memory devices,because it does not contain Bi and Pb.Moreover,the YMnO₃ thin films have a relatively low permittivity(ε_r=20) and a single c-axis polarization.The mainly work of the thesis are as follows.1,Hexagonal YMnO₃ films have been prepared on Si(100) substrates by chemical solution method(CSD),and the effect factors of the highly c-axis oriention films were discussed.P-E hysteresis loops of metal/ferroelectric/metal capacitors using hexagonal YMnO₃ films deposited on Si(111) substrate was measured.From the results of the measurement,it is seen that the films have well ferroelectric performance.2,The temperature-depended Raman spectrum of hexagonal YMnO₃ films and powder prepared by CSD were investigated.7 Raman peaks of YMnO₃ films were observed at room temperature.From the results of the temperature dependence of Raman spectrum,it is deduced that the YMnO₃ films have magnetic phase transition temperature at about 123 K.The origin of higher T_N of the film than that of the powder or bulk is also briefly discussed.3,The partly c-axis oriention hexagonal YMnO₃ films were deposited on 3C-SiC (111) substrate using CSD.The samples were characterized using XRD,SEM,Raman and XPS.Polarization versus electric field measurements on metal/ferroelectric/metal capacitors was obtained using a radiant precision workstation ferroelectric tester.4,The YMnO₃ nanorods were successfully prepared by a hydrothermal method. X-ray diffraction(XRD) results demonstrate that the YMnO₃ nanorods were composed of pure hexagonal YMnO₃.SEM,HRTEM and SAED techniques were used to study composition,crystallinity,morphology and size of the as prepared YMnO₃ nanorods.It can be observed that the nanorods have uniformity,smooth surface and hexagonal structure.Combining with the results of the XRD and SAED, it is suggested the YMnO₃ nanorods have been grown along<001>direction.The temperature dependent magnetization of the samples was performed.A spin glass feature was observed,which is due to the uncompensated spin of the surfaces.