DOPING EFFECTS ARISING FROM FE AND GE FOR MN IN LA0.7CA0.3MNO3

Structural, magnetic, and transport properties of polycrystalline La0. 7Ca0.3Mn1-xFexO3 and La0.7Ca0.3Mn1-xGexO3 are experimentally studied. Single-phase samples are obtained in the range x = 0 - 0.12 for Fe, an d x = 0 - 0.06 for Ge. There are no appreciable structure changes due to the introduction of Fe and Ge. The Mn-site doping favors a reduced magnetic/resistive transition, at rates of similar to 22 K for 1% Fe a nd similar to 28 K for 1% Ge, and an elevated resistivity. No metal-in sulator transition occurs when the content of Fe exceeds similar to 0. 1. The enhanced doping effects in La0.7Ca0.3Mn1-xFexO3 can be ascribed to the reduced hole concentration noting that the presence of Fe and Ge influence the contents of mobile e(g) electrons and holes in the co mpounds, respectively. Equivalence of the effects from Fe and Ge dopin g, respectively, to those due to e(g) electron and hole trapping and t he relation between Mn- and O-site doping are discussed. (C) 1998 Amer ican Institute of Physics. [S0003-6951(98)01446-6].