The effect of NiO doping on the structure, magnetic and magnetotransport properties of La_(0.8)Sr_(0.2)MnO_3 composite

摘要

The effect of NiO doping on the structure, magnetic and magnetotransport properties of La_(0.8)Sr_(0.2)MnO_3 (LSMO)/xNiO has been investigated. These studies show that some part of the NiO goes into the perovskite lattice substituting Mn in LSMO and remainder segregates as a separate phase at the grain boundaries and grain surfaces. The presence of NiO at the grain boundaries increases the disordered states at the surface of the grains and therefore the low temperature resistivity increases very quickly by the increase of NiO doping level. Results also show that the NiO doping has an effect on a LFMR. The value of MR increases for low doping level of 0 < = x < = 3 and decreases at high doping level of x > = 5. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increasing of LFMR at x < = 3, while reduction of LFMR at x > = 5 originates from substitution of Ni~(2+) for the Mn~(3+) ions introduces the magnetic dilution into the samples.