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 Ln(0.5)Ca(0.5)MnO(3) (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 T-m([r(A)]) magnetic diagram, where [r(A)] is the A site cationic average radius, is established for the oxides Ln(0.5)Ca(0.5)Mn(1-x)Cr(x)O(3), which demonstrates that [r(A)] is not a rhedibitory parameter for the occurrence of colossal magnetoresistance (CMR) properties. The average size limit [r(A)](L) approximate to 1.19 Angstrom below which the MI transition is suppressed in the undoped CO compounds is indeed lowered to [r(A)](L) approximate to 1.14 Angstrom 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. (C) 1997 American Institute of Physics.