Magnetoresistance behaviour of La0.7Sr0.3MnO3 /NiO composites

(La0.7Sr0.3MnO3)1−x/ (NiO)x ( x ∼ 0 , 0.05, 0.10, 0.15 and 0.20) composites were prepared via a solid state reaction process. Detailed studies of magnetic and magnetotransport properties of the composite samples have been performed. X-ray diffraction and scanning electron microscopy observations reveal that there is no evidence of reaction between the La0.7Sr0.3MnO3 (LSMO) and NiO grains. It has been observed that the incorporation of NiO phase into the La0.7Sr0.3MnO3 matrix lowers the metal–insulator transition temperature ( T p ) . Magnetic measurement reveals that the ferromagnetic order of LSMO is weakened by addition of NiO. An enhancement in magnetoresistance (MR) is observed at low temperature, below 120 K, for the composites with x = 0.05 , x = 0.10 and x = 0.15 and at high temperature (near room temperature) for all the composites at applied magnetic field H ∼ 3 kOe. In the present work, it is suggested that the large MR at low temperature (below 120 K) is low field magnetoresistance (LFMR) caused by spin polarized tunneling, whereas at around room temperature it is high field magnetoresistance (HFMR) caused by magnetic disordering.