Extension of colossal magnetoresistance properties to small A site cations by chromium doping in Ln0.5Ca0.5MnO3 manganites

The Mn site substitutions of charge ordered (CO) manganites Ln0.5Ca0.5MnO3 (Ln=La–Tb) have been investigated. Among the different studied doping elements, chromium is shown to be the most efficient one to induce a metal insulator (MI) transition in the CO undoped insulators. A new Tm(〈rA〉) magnetic diagram, where 〈rA〉 is the A site cationic average radius, is established for the oxides Ln0.5Ca0.5Mn1−xCrxO3, which demonstrates that 〈rA〉 is not a rhedibitory parameter for the occurrence of colossal magnetoresistance (CMR) properties. The average size limit 〈rA〉L≈1.19 Å below which the MI transition is suppressed in the undoped CO compounds is indeed lowered to 〈rA〉L≈1.14 Å in the Cr-doped materials. The electron microscopy study of these Cr doped oxides shows that this spectacular effect corresponds with the disappearance of the structural transition associated with CO.