Abstract
The effect of quenched disorder on the magnetic and transport properties of (La1-xNdx)(2/3)(Ca1-ySry)(1/3)MnO3 polycrystalline samples with (J1(x=0, y=0); J2(x=0.05,y=0.04); J3 (x=0.25,y=0.20); J4(x=0.3,y=0.24); J5(x=0.98,y=0.8) is analyzed within the context of percolative transport and the existence of the Griffiths phase. Our results demonstrate that moderate-small chemical disorder affects the inverse dc susceptibility x(-1)(T) at higher temperature revealing the presence of the Griffiths phase above the Curie temperature. We attribute the observed anomalous paramagnetic behavior to the magnetic heterogeneity caused by the segregation of short-range ferromagnetic clusters within the paramagnetic matrix. The electrical properties show the presence of a metal-insulator transition at T-MI which decreases with increasing disorder sigma(2). In the low-temperature ferromagnetic metallic region, the p data follow an empirical relation, rho(FM) = rho(0) + rho T-2(2) + rho T-4.5(4.5) reflecting that the conductive mechanism mainly arises from electron-electron, electron-phonon and electron-magnon scattering changed versus disorder effect. In the high-temperature paramagnetic insulating region, the rho data for all samples follow the adiabatic small-polaron-hopping model. To understand the dependence of disorder with transport mechanism, we used the phenomenological equation for conductivity under a percolation approach, which is dependent on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Also we demonstrate that magnetoresistance (MR) increase with increasing disorder sigma(2). It is very interesting to note that the MR at room temperature is enhanced, which is encouraging for potential applications. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.