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

The effect of quenched disorder on the magnetic and transport properties of (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 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−1χ−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 TMI which decreases with increasing disorder σ 2. In the low-temperature ferromagnetic metallic region, the ρ data follow an empirical relation, ρFM=ρ0+ρ22T+ρ4.5T4.5ρFM=ρ0+ρ2T2+ρ4.5T4.5 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 σ2. It is very interesting to note that the MR at room temperature is enhanced, which is encouraging for potential applications.