Effect of mn-site doping with nickel on the electric and magnetic properties of Sm_0.55Sr_0.45MnO₃ manganites

We present the effect of Ni-ions doping on the magnetoresistance and magnetic properties of Sm_0.55Sr_0.45 Mn_1−xNi_xO₃ 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 Sm_0.55Sr_0.45Mn_1−xNi_xO₃ 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.