Soledad-Flores, Olga V.

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    Tuning of structural and magnetic properties of La1−xSxMnO3
    (2018) Soledad-Flores, Olga V.; Perales-Pérez, Oscar J.; College of Arts and Sciences - Sciences; Lysenko, Sergiy; Department of Physics; Resto-Irizarry, Pedro J.
    This thesis investigated the effect of incorporation of Sr2+ and Ca2+ ions on the structural and magnetic properties of LaMnO3 (LMO) powders synthesized by sol-gel and thermal treatment method at 900°C. X-ray diffraction measurements showed diffraction patterns that belong to LMO perovskite structure for the all the samples; no impurity peaks were observed. The magnetization versus applied field measurements evidenced the antiferromagnetic nature of non-doped LMO. On the other hand, an evident ferrimagnetism was observed in all Sr-LMO samples, which was explained in terms of the types of interaction exchanges between manganese and oxygen ions in neighboring cells. The maximum magnetization of 41.6 emu/g a coercivity of 43.61 Oe were achieved for the 25% Sr-doped LMO. X-ray diffraction of Ca-LMO powders showed diffraction patterns typical of the perovskite structure. These samples exhibited paramagnetic behavior, due to the null contribution of Bohr magnetons of the Ca2+ ion. Also, the diffraction peaks characteristic of pure LMO perovskites were observed in all Sr2+/Ca2+ co-doped samples. The incorporation of Ca2+ in the structure of the perovskite caused the drop in the maximum magnetization from 41.6 emu/g to 15 emu/g. This can be explained on the basis of the null contribution of Bohr magnetons of Ca2+ ions, although the ferrimagnetic behavior was maintained due to the presence of Sr species. The incorporation of Ca+2 in the LMO cell would reduce the magnetization but also helped to decrease the Curie Temperature, as evidenced by the results obtained. A subsequent optimization on the particle size that would cause the Curie Temperature drop even more- will be required to take full advantage of the Ca incorporation effect as Curie temperature tuning factor.