The influence of disorder on the appearance of Griffiths phase and magnetoresistive properties in (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 oxides

Abstract

Abstract The effect of quenched disorder on the magnetic and transport properties of (La 1− x Nd x ) 2/3 (Ca 1− y Sr y ) 1/3 MnO 3 polycrystalline samples with ( J 1 ( x =0, y =0); J 2 ( x =0.05, y =0.04); J 3 ( x =0.25, y =0.20); J 4 ( x =0.3, y =0.24); J 5 ( 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 χ − 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 σ 2 . In the low-temperature ferromagnetic metallic region, the ρ data follow an empirical relation, ρ F M = ρ 0 + ρ 2 T 2 + ρ 4.5 T 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 ρ 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 σ 2 . It is very interesting to note that the MR at room temperature is enhanced, which is encouraging for potential applications.