(la <sub> 0.83 </ Sub> Of Mno <sub>, Of Sr <sub> 0.17 </ Sub> 3 </ Sub>) <sub> 1-x </ Sub> (ito) <sub> X </ Sub > Giant Magnetoresistance Effect Of The Composite System

Perovskite-type La_0.83Sr_0.17MnO₃ (LSMO) powder samples were synthesized by the sol-gel method. The composites (La_0.83Sr_0.17MnO₃)_1-x(ITO)_x [ITO = (In₂O₃)_0.95(SnO₂)_0.05] were fabricated by mechanically mixing LSMO and ITO powders through the ultrasonic vibration method. The mixture was pressed into small strips and then sintered at 1250 °C for 10 h.The structure of the samples was represented by x-ray diffraction (XRD). The XRD spectra of the composites display two different sets of lines, which can be indexed by pure LSMO and ITO, respectively. The morphology was observed through scanning electronic microscopy (SEM). It is found that LSMO grains embed in ITO network. The XRD and SEM indicated that no observable chemical reaction occurs between LSMO and ITO. Detailed studies of magnetic and transport properties for composites have been performed. The magnetization was measured by a vibrating sample magnetometer. There is a obvious discrepancy in the M versus T curve for different samples. The possible cause for the difference could be the doping effect of In ions into A sites of LSMO.Measurements of the resistance and the magnetoresistance were performed by using a standard four-probe technique and an applied field. A giant positive magnetoresistance (PMR) has been observed above T_c for samples with x around 0.40. Especially for(La_0.83Sr_0.17MnO₃)_0.6(ITO)_0.4, the magnetoresistive ratio (MR = (ρ_H - p₀)/ p₀, where ?_H and ?₀are the resistivity under a magnetic field and zero field, respectively) for PMR can reach 39.3% under a magnetic field H = 224kA/m. Meanwhile, the negative magnetoresistance (NMR) related to spin-dependent interfacial tunneling is observed below T_c and the MR can reach -15% under a same field H = 224kA/m. It is much larger than that observed in pure La-Sr-Mn-0 granule. Theoretical analysis suggests that the magnetic-field-induced broadening of the p-n barrier between both kinds of grains and the suitable density of the p-n heterostructures should be responsible for the PMR behavior.