Effect of Mn-Site Doping with Nickel on the Electric and Magnetic Properties of Sm0.55Sr0.45MnO3 Manganites

We present the effect of Ni-ions doping on the magnetoresistance and magnetic properties of Sm0.55Sr0.45Mn1−xNixO3 in the temperature range 4.2–300 K and the magnetic field range 0–90 kOe, for 0<x<10 %. The Ni-ion doping significantly reduces the metal-ferromagnetic to insulating-paramagnetic transition temperature (TC). The Sm0.55Sr0.45Mn1−xNixO3 undergoes a transition from low-temperature ferromagnetic metallic state to high-temperature paramagnetic insulating-like state. Magnetic susceptibility measurements for samples with various Ni-concentrations showed a reduction in the paramagnetic transition temperature with increasing Ni-concentration. Moreover, the sharp peak in the susceptibility shown by the Ni-free samples has disappeared completely. The susceptibility becomes more round at 10 % Ni, while for lower Ni-concentration it becomes flat, indicating almost pure ferromagnetic behavior. Magnetization isotherms measurements have also been performed for Ni-ions samples doped with up to 10 %. With increasing Ni-doping, the irreversibility region in both M vs. T and M vs. H curves have decreased considerably, almost vanishing at 5 % Ni. For 5 % Ni and above, the FC and ZFC states basically coincide on top of each other, no spin-glass-like transition has been seen.