Probing the effects of pH and sintering temperature on the structure and magnetic properties of La0.833Ag0.167MnO3

This work highlights the effects of pH and sintering temperature modifications on the structural, magnetic and magneto-transport properties of La_0.833Ag₀.₁₆₇MnO₃, prepared by sol-gel route. The structural studies revealed that all the pH varied samples crystallized in R-3c space group. Minor impurity phases of Ag and Mn₃O₄ were detected in the XRD patterns of the samples synthesized at lower pH. Phase quantification by Rietveld refinement revealed that the concentration of impurity phases showed an inverse relation to pH. The existence of impurity phase is effectively elucidated, using the concept of chelating property of citric acid. FESEM analysis indicated that pH variation had no significant effect on the particle size; however, the grain size is gravely affected by sintering temperature. Magnetic studies showed that pH variation have negligible effect and all the samples exhibited ferromagnetic nature, with T_C = 297 ± 2 K. Transport studies revealed that the material resistivity is strongly modified by variations in both pH and sintering temperature. Double metal insulator transition (MIT) peak, which is an inherent feature on the transport curve, becomes increasingly discernible with the enhancement in pH. All the pH varied samples exhibited very high magnetoresistance proprty, irrespective of Ag and Mn₃O₄ impurity phases. The present study emphasize that phase purity of La_0.833Ag₀.₁₆₇MnO₃ is strongly dependent on pH of the precursor. The study showed that for single phase well crystallized sample, pH > 10 and sintering temperature 1273 K is ideal. The magnetotransport property of the samples in the low temperature regime is comprehended on the basis of spin polarized tunneling model, while in the high temperature regime, percolation model is employed.

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