Anomalous variation of magnetoresistance in Nd0.67−yEuySr0.33MnO3 manganites

A systematic investigation of Eu-doped Nd-based colossal magnetoresistive manganites with compositional formula Nd0.67−yEuySr0.33MnO3(y=0–0.67) has been undertaken to understand their structural, magnetic as well as electrical behavior. These materials were prepared by the citrate gel route, and were later characterized by X-ray diffraction (XRD), AC susceptibility, electrical resistivity etc; measurements. A detailed structural characterization of the XRD data has also been undertaken, using Rietveld refinement method. From a systematic analysis of electrical resistivity versus temperature data, it has been found that the last two samples of the series ( y = 0.57 and 0.67) are found to exhibit charge order (CO) phenomenona, and that the CO state melts completely in the case of former sample ( y = 0.57 ) while it melts partially only in the case of later one ( y = 0.67 ) , even in a magnetic field of 7 T. The observed behavior has been explained qualitatively. Some of the samples of the series are found to exhibit unusually large magnetoresistance over a wide temperature range in the low temperature region, and their behavior has been explained on the basis of phase segregation and an inter-grain spin polarized tunneling effect.