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The effect of Al substitution on charge ordered Pr0.5Ca0.5MnO3: structure, magnetism and transport

We report on the effect of Mn site substitution of Al on the structural, magnetic and transport properties of charge ordered Pr0.5Ca0.5MnO3. This substitution introduces non-magnetic impurities in the Mn–O–Mn network, causes the Mn3+/Mn4+ ratio to deviate away from unity and is seen to predominantly replace Mn4+ without introducing any appreciable change in the structure. The strength of charge ordering is suppressed with increasing Al doping, as is seen from AC susceptibility, the magnetocaloric effect and DC resistivity. The observation of traces of charge ordering over an extended range of impurity doping of 10%, besides being indicative of the robust nature of charge ordering in Pr0.5Ca0.5MnO3, also underscores the relatively insignificant effect that Al substitution has on the lattice distortions and the importance of non-magnetic substitutions. For all the samples, the conductivity in the temperature range above the charge ordering transition is observed to be due to the adiabatic hopping of small polarons, whereas below the charge ordering transition, Mott’s variable range hopping mechanism is seen to be valid.