STRUCTURAL, ELECTRICAL AND MAGNETIC PROPERTIES OF Pr1-xBaxMnO3(x=0.33–0.80)

Abstract

We report here the electrical resistivity, ac susceptibility, low field magneto-resistance (LFMR) and structural parameters of the Pr 1-x Ba x MnO 3(x= 0.33–0.80) system. Samples with 33% and 40% Ba -content exhibit two clear transitions in their resistivity-temperature behavior while signatures of higher temperature transition are also seen in the 50% Ba sample. The higher temperature transition (insulator-metal, Tp1), like in other CMR materials, results due to competition between the double exchange and super exchange mechanisms. The lower temperature broad hump (Tp2) in resistivity reflects the strain effect at the grain boundaries due to the ionic radii mismatch between Pr +3 and Ba +2. The low field magneto-resistance (at 0.15T) also corroborates the above results as MR peaks near Tp1 and increases further at lower temperatures, reflecting the contribution from the grain boundaries. Susceptibility measurements show the Curie transition (Tc) to be near Tp1 of the ρ-T data. Results are found to be consistent with the (NdBa) MnO 3 and (LaBa) MnO 3 systems. Resistivity data on the Pr 0.67 Sr 0.33 MnO 3 system, where the lower temperature transition at Tp2 is not seen due to the smaller ionic size difference of ( Pr +3– Sr +2) compared to ( Pr +3– Ba +2), also substantiate these results. The observed resistivity upturn at low temperatures is considered in terms of the ensuing localization of carriers due to the varying degree of ionic size mismatch in these systems.