Charge and magnetic order suppression by Mn site doping in layered and three-dimensional manganites

A systematic study of the doping of the Mn sites by various elements (Mg2+, Fe3+, Al3+, Sn4+, Ti4+) in three charge ordered manganites -La0.5Sr1.5MnO4, LaSr2Mn2O7 and Pr0.5Ca0.5MnO3- has been performed. An abrupt disappearance of the charge ordered state is observed, for low level of dopant (similar to 1-2%) whatever its nature. The change of slope associated to the charge ordering on resistivity curves as well as the coupled antiferromagnetic transition on susceptibility curves indeed tend to disappear. However, whereas magnetoresistance properties are not significantly modified in the case of the layered manganites La0.5Sr1.5MnO4 and LaSr2Mn2O7, huge magnetoresistance is induced in the case of the three-dimensional (3B) manganite Pr0.5Ca0.5MnO3. These strong modifications of the transport properties are discussed in the light of the magnetic properties. (C) 1998 Elsevier Science B.V. All rights reserved.