Electrical Transport and Magnetic Behaviors of La0.67Sr0.33Mn1-xBxO3 (B = Cr, Ru)

Polycrystalline samples of La0.67Sr0.33Mn1-xCrxO3 (with x=0, 0.05 and 0.1) and La0.67Sr0.33Mn1-xRuxO3 (with x = 0.05 and 0.1) were synthesized using the conventional solid state reaction route and found single phase in nature. Electrical resistivity measurements as a function of temperature in range 5 K-400 K and as a function of magnetic field up to 5 Tesla were pertbrmed using d.c. four-probe method. Magnetization data were acquired as a function of temperature in a range 10 K-400 K with an applied magnetic field of 500 Oe. When Mn is partially substituted by Cr and Ru the system displays dramatic changes in the electrical transport behavior and shows double-peaked feature in resistivity curve. Both Cr and Ru substitutions effectively reduce insulator-metal transition (T-P) and paramagnetic-ferromagnetic transition (T-C) temperatures implying that there might exist FM interaction between Mn+3 and Cr3+ as well Mn+3 and Ru+4. The largest low-temperature magnetoresistance (MR%) is attributed to grain boundary effects and difference in size disorder for Cr and Ru substituted compounds.