Peculiarities in the electrical and magnetic properties of cobalt perovskites Ln(1-x)M(x)CoO(3) (Ln(3+): La3+, M2+: Ca2+, Sr2+, Ba2+; Ln(3+): Nd3+, M2+: Sr2+)

We refer here to the electrical and magnetic properties of the Ln(1-x)M(x)C oO(3) systems (Ln(3+): La3+, M2+: Ca2+, Sr2+, Ba2+; Ln(3+): Nd3+, M2+: Sr2), paying special attention to those ferromagnetic compounds that display M -I transitions as temperature rises: La1-xMxCoO3 (M2+: Ca2+, Sr2+, Ba2+) in the compositional interval x=0.2-0.3, and Nd1-xSrxCoO3, with x=0.40. The m agnetotransport properties of such materials are peculiar and interesting: they show diodic behavior and large relaxation effects - these latter being specially important in the Nd compound - they display magnetoresistive eff ects specially at the M-I transition temperatures, and they age with rime. All these results are discussed on the basis of the inhomogeneous electroni c structure of these doped cobalt perovskites and taking into account the i nfluence of the lanthanide ion on their magnetic and electrical properties. (C) 1999 Elsevier Science Ltd. All rights reserved.