Enhanced electrical/magneto-transport properties in La0.68Nd0.04Ca0.28MnO3/Agx composites under a low magnetic field

High temperature coefficient of resistivity (TCR) and magnetoresistance (MR) have been long-pursuing goals for perovskite manganites to be used in infrared detectors and magnetic sensors, etc. Here, a series of La0.68Nd0.04Ca0.28MnO3/Agx composites were prepared by sol–gel method combined with solid-state reaction. The crystal structure, surface morphology, chemical composition, element valence, and electrical transport characterizations of the samples are systematically studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray photoemission spectroscopy (XPS), and four-probe method. XRD spectra reveal that all composites crystallized in orthorhombic perovskite structure. SEM displays that the addition of Ag makes the grain boundary more obvious as compared with the sample without Ag. The EDS results show that specimens contain La, Nd, Ca, Mn, O, and Ag elements without any impurity. The content of Ag visibly affected the ratio of Mn4+/(Mn3+ + Mn4+) in XPS spectra. With the addition of Ag, the TCR and MR of the composites have been significantly improved. To be specific, the sample with x = 0.1 demonstrates high TCR (41.79% K−1) and MR (87.44%) at 1 T magnetic field, and the former can reach up to 46.59% K−1 in the absence of a magnetic field.