Strontium adding effects in Pr_0.65Ca_0.35MnO₃

Abstract
The manganese compounds with a perovskite structure are a hot topic in the Materials Science due to the high variation of the electrical resistivity under a magnetic field called colossal magnetoresistance (CMR). This effect is maximum near the Curie temperature (Tc) when the materials become ferromagnetic (FM). Nevertheless, the double exchange interaction, that produces this FM state, competes with other interactions (as the antiferromagnetic (AFM) superexchange and structural distortions). When these last effects are more important the manganite evolves to an insulator, AFM and in some cases with charge order localization (CO) of Mn³⁺ and Mn⁴⁺. We study the solid solution Pr_0.65Sr_xCa_0.35-xMnO₃ with x between x=0 and x=0.20 prepared by decomposition of metal nitrates route. Our magnetic and transport measurements show how the CO is destroyed while we add Sr, changing from semiconducting behavior (x=0) to FM metallic (x=0.20). SEM photographs show that all samples have 1-5 micrometers grain size. No frequency dependence (33 Hz-33KHz) was observed in x=0 sample, indicating that the grain size do not affect the dielectric properties.