Mg doping of LaSrFe manganite: Magnetic and electric study

The temperature dependence of magnetic susceptibility χ (Τ), 78<Τ(Κ)<295, and electrical resistivity ρ (T), 1059.634) decreases to a minimum for sample x=0.6. Highest resistivity (ρ) and ac susceptibility (χ) are observed for x=0.6. Metal- semiconductor transition temperature Tρ decreases gradually with Mg doping, in contrast to ferromagnetic-paramagnetic Curie temperature Tc which shows weak dependence on Mg doping level. Low temperature resistivity showed upturn in the temperature range 28-37 K. At high temperatures, variable range hopping conduction predominates with density of states N(Ef) ~3×1019−6×1019 (eV−1 cm−3). Low temperature resistivity follows ferrometallic nano-particle relation: ρ=ρo +ρ1T2 +ρ2T4.5. AC susceptibility of x=0.0 and 0.6 fit well to Curie law, samples x=0.2, 0.4, 0.8 and 1.0 are better described in the framework of Neel ferrimagnetism. Transport and magnetic susceptibility results are interpreted in terms of core-shell model where ferromagnetic core interacts anti-ferro-magnetically with ferromagnetic shell.