Chinchay-Espino, Héctor A.

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    Tuning of multifunctional properties of undoped and doped BiFeO3
    (2018) Chinchay-Espino, Héctor A.; Perales-Pérez, Oscar J.; College of Arts and Sciences – Sciences; Fernández, Félix; Lysenko, Sergiy; Department of Physics; Gregory Crespo, Alexandra
    This work studied the effect of the incorporation of Co2+ and Mn2+ species on the structural and magnetic properties of nanocrystalline powders of BiFeO3 (BFO) synthesized by the sol-gel and thermal treatment method at 700°C for 15, 30 and 45 mins. X-ray diffraction (XRD) measurements showed diffraction patterns that belong to the rhombohedral perovskite structure of BiFeO3 for all undoped samples. Minimum presence of impurities was obtained for samples thermally annealed for 30 minutes. The measurements of magnetic hysteresis loops indicated that undoped BFO samples exhibited antiferromagnetic ordering, with a maximum magnetization obtained at 30 minutes of annealing time. XRD measurements verified the rhombohedral perovskite structure for Co-BFO samples. However, a secondary phase of Ferrite Cobalt (CFO) was detected for 9, 10 and 15% Co; the formation of CFO inhibited the growth of the impurity phases. Magnetic hysteresis measurements evidenced a ferromagnetic behavior for all Co-BiFeO3 samples due the presence of CFO. A saturation magnetization of 4.13 emu/g and a coercivity of 1083.4 Oe were achieved at 15 % of Co. On the other hand, XRD measurements showed that the Mn-doped BFO samples exhibited a rhombohedral perovskite structure only for 3% Mn. Samples at 5% and 7% Mn reported the tetragonal structure, which was attributed to the incorporation of Mn(II) species in Bi sites. The relative amount of impurity phases increased with time owing decomposition of BFO. These paramagnetic impurity phases affected the corresponding magnetic properties. Magnetic characterization revealed a ferrimagnetic behavior in the 7% Mn-BFO powder, whereas a paramagnetic trend was observed for other compositions. The optimal doping condition was reached at 7% Mn with a ferrimagnetic order and a maximum magnetization of ~ 0.68 emu/g.