Suppression of charge-ordering and appearance of magnetoresistance in a spin-cluster glass manganite La0.3Ca0.7Mn 0.8Cr0.2O3

Abstract

The magnetic properties of electron-doped manganite La0.3Ca0.7MnO3and La0.3Ca0.7Mn0.8Cr0.2O3polycrystalline samples prepared by sol-gel technique have been investigated between 5 and 300K in magnetic fields ranging from 0 to 5T. The transition at 260K, attributed to charge ordering in La0.3Ca0.7MnO3, is completely suppressed in the Cr-substituted sample while the onset of a magnetic remanence followed by the appearance of a magnetic irreversibility at lower temperatures is observed in both samples. These features indicate that ferromagnetic clusters coexist with either an antiferromagnetic phase for La0.3Ca0.7MnO3or a spin-cluster glass phase for La0.3Ca0.7Mn0.8Cr0.2O3at the lowest temperatures. The exponential temperature dependence of the resistivity for the Cr-substituted sample is consistent with the small polaron hopping model for 120K<T<300K, while the data are better described by Mott's hopping mechanism for T<120K. Whereas the parent compound La0.3Ca0.7MnO3is known to show no magnetoresistance, a large negative magnetoresistance is observed in the La0.3Ca0.7Mn0.8Cr0.2O3sample below 120K. The appearance of the CMR is attributed to spin dependent hopping between spin clusters and/or between ferromagnetic domains. © 2003 Elsevier B.V. All rights reserved.