Investigations Of Multiferroicity In Manganites Dy(Mn_1-xFe_x)O₃

Multiferroics refers to a new type of multifunctional materials, which possesses two or more ferroics such as ferroelectric, ferromagnetic and ferroelastic(only in some materials). Multiferroics has the vast application potentials in spintronics and high density information storages, due to combine the advantage of ferroelectric and ferromagnetic materials, respectively. The representative multiferroics DyMnO3 is investigated in the article. We systematacially study the effects on crystal structure, magnetic, ferroelectric, and dielectric properties of the rare-earth manganites by doping, adjusting temperature and modulating the external magnetic field. The article mainly contains contents as follows:(1) The DyMn1-xFexO3 polycrystalline ceramic samples were successfully synthesized by conventional solid-state reaction. Meanwhile, the processes for preparation material and testing technology on this article are recommended briefly.(2) The crystal structure of the DyMn1-xFexO3 polycrystalline ceramic samples and its magnetic properties in the steady magnetic field are detailly researched. First, Rietveld profile refinement on the XRD date using the GASA program shows that polycrystalline ceramic samples are condensed along the b axis and stretched along the c axis by Fe doping. Secondly, the independent Dy3+ spin order is significantly suppressed by partial Fe-substitution of Mn ions. In addition, this is a new discovery in our article that the ZFC/FC curve about DyMn0.90Fe0.10O3 has a remarkable bifurcation at T ~ 30 K and it has about 800 Oe coercivity and 1.7emu/g remanent magnetization.(3) The pulsed high magnetic field and the measuring technique on magnetization are illuminated in detail. Particularly, the fabricating mechanism of signal coils, compensation coils and the confirming conversion factor of magnetic field coils are systematically introduced on the measuring rod. Then, the magnetic properties of the DyMn1-xFex O3 polycrystalline ceramic samples are researched in the pulsed high magnetic field. We firstly confirm the samples without new phase transition under the high magnetic field. Moreover, the magnetization about DyMn1-xFexO3 is not saturated even 0 ~ 50 T, due to the obvious spin of frustrion about samples.(4) The ferroelectric and dielectric physical properties of the DyMn1-xFexO3 polycrystalline ceramic samples are systematically investigated. Low temperature ferroelectric and phase transition temperature of TN ~ 40 K, TC ~ 19 K, TDy ~ 10 K about DyMnO3 are confirmed. For multiferroics DyMnO3, electric polarization is significantly enhanced by proper magnetic field and Fe-doping. It is indicated that the DyMn1-xFex O3 samples have a strong magnetoelectric coupling effect. Furthermore, researches show that the magnetic field is advantageous to the dielectric properties of the samples. However, the modulating ability about the sample of dielectric properties is getting weak with the increasing of Fe ions doping.