Abstract
Polycrystalline La(0.70)Sr(0.30)Mn(1-y)FeyO(3) (0.05 <= y <= 0.07) samples are prepared by the co-precipitation method and have been studied. The substitution of Mn3+ by Fe3+ reduces the number of available hopping sites for the Mn e(g)(up arrow) electron and suppresses the double exchange (DE), resulting in the reduction of the metal-semiconductor transition temperature (T-P) and the flux density saturation (B-s). Low-temperature resistivity (rho) data (below T-P) well fit with the relation rho(T) = rho(0)+rho T-2(2), indicating the importance of grain/domain boundary effects and electron-electron scattering processes in the conduction of these materials. On the other hand, at high temperature (T-P < T < theta(D)/2) conductivity data satisfy the variable range hopping (VRH) model. For T > theta(D)/2 the small polaron hopping model is more appropriate than the VRH model. (C) 2008 Elsevier B.V. All rights reserved.