Magnetoresistance Effect in La1.5Sr0.5NiO4-Doped La0.7Ca0.3MnO3 Nanocomposites

Our experimental results point out that most La1.5Sr0.5NiO4 nanoparticles were distributed at the grain boundaries and on the surfaces of the La0.7Ca0.3MnO3 nanoparticles. The nanocomposite samples exhibit a ferromagnetic-paramagnetic and a metal-insulator phase transitions at TC and TMI, respectively. With increasing La1.5Sr0.5NiO4-doped content, TC value is almost unchanged while TMI value decreases from 251 K for an undoped sample to 65 K for 20 % La1.5Sr0.5NiO4-doped one. Particularly, the La1.5Sr0.5NiO4-doped samples higher than 20 % exhibit the insulating properties in the whole temperature range. Magnetoresistance effect at low field (H= 3 kOe) of all the samples is observed. In order to explore the nature of their magnetoresistance effect at low field according to temperature and magnetic field change, we analyzed carefully the obtained data based on the phenomenological model related to the spinpolarized transport of conduction electrons at grain boundaries. With this, the temperature dependences of magnetoresistances (including the intrinsic magnetoresistances and spinpolarized transport magnetoresistances) can be described well by an expression of the Curie-Weiss law-like behavior, a + b/(c + T). We also have been able to observe the percolation threshold in this system for 25 % of La1.5Sr0.5NiO4 component, and around this critical point a great increase of magnetoresistances has been detected.