| Multiferroic materials are materials which ferroelectric coexists with ferromagnetic, and exhibit magnetoelectric coupling effect between them. Magnetoelectric effect provides more research directions for the development of new types of microelectronic devices, particularly in the field of information storage devices. Scientists have always paid high attention to the research of multiferroic materials. Rare earths manganese oxides(RMn2O5) belong to single-phase multiferroic materials. The interactions between the magnetic moments of Mn3+, Mn4+ and rare earth ions make it show complex magnetic properties. Currently, as to the preparation study of RMn2O5, there still needs further study to obtain the nanosized materials as well as controllable synthesis of size and morphology. Hydrothermal method is being widely used in the preparation of inorganic material powders because of its simple process, controllable synthesis and good dispersibility. On the basis of hydrothermal method, there are many parameters can be controlled to obtain ideal nanosized material powders.In this paper, we added organic additives into the reaction precursor solution in order to improve hydrothermal synthesis. RMn2O5(R = Yb, Tb, Tm, Sm) nanosized materials were synthesized, besides, the morphology and size of the products were controlled by changing the reaction parameters. The products were further investigated by the measurements of XRD, SEM, TEM, IR, Raman and SQUID. We studied and discussed the relationship between morphology, size and magnetic properties.(1) Yb Mn2O5 nanorods were obtained by CTAB-assited hydrothermal synthesis, and the increasing amount of CTAB can shorten the length of nanorods. Urchin-like Yb Mn2O5 microspheres were successfully synthesized by a EDTA-assisted hydrothermal mehod. EDTA prompted the fromation of nanoparticles and aggregated together themselves, then the oriented growth of nanoparticles on the surface of the aggregates induced to the formation of urchin-like microspheres. Yb Mn2O5 showed weak ferromagnetic at low temperatures, which was ascribed to the incompensate spin magnetic moments on the surface. For urchin-like microspheres, the divagation between FC and ZFC curves at 8 K was observed, which was related to Yb3+ magnetic ordering. As the size of nanorods increases, the temperature of divagation ralated to Mn ions magnetic moments decreases. The coercivity and exchange bias field increases first and then decreases.(2) Tb Mn2O5 with good crystallinity were synthesized by different surfactant-assisted hydrothermal methods. Upon a certain amount of different surfactant, pure products were synthesized by hydrothermal method. Through the experiment of the amount of arabic gum, we found that the effect of the amount on controllable synthesis was obvious. Magnetic properties indicated Tb Mn2O5 showed weak ferromagnetic, which was explained by uncompensated spins on the surface. The ferromagnetic transition temperature was 40 K. The divagation between FC and ZFC curves at 5 K or 6.5 K was related to Tb3+ magnetic ordering, and the temperature increased with the increasing of the size. The coercivity decreases as the size of nanorods decreases.(3) The different morphology and size of RMn2O5(R = Sm, Tm) nanosized powders were synthesized by simple and arabic gum-assisted hydrothermal method. Arabic gum was conducive to the growth of rare earth manganese oxides nanorods, and prompted the formation of complex Sm Mn2O5 morphology. Smaller Sm Mn2O5 nanorods were prepared by a hydrothermal method with adding PEG-4000. For different rare earth manganese oxides, the control of additives on morphology and size of products was not all the same. Magnetic measurements indicated that Sm Mn2O5 presented weak ferromagnetic at low temperatures, Sm3+ spin magnetic moment became ordered arrangement at 4 K. |
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