Anomalous variation of magnetoresistance in Nd0.67−yEuySr0.33MnO3 manganites
G. Venkataiaha, V. Prasadb and P. Venugopal Reddya, ,
aDepartment of Physics, Osmania University, Hyderabad 500 007, India bDepartment of Physics, Indian Institute of Science, Bangalore 560 012, India
Received 17 May 2006; revised 16 July 2006; accepted 27 September 2006. by E.G. Wang. Available online 20 October 2006.
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.
Keywords: A. Manganite; B. Sol–gel technique; C. Grain boundary; D. Magnetoresistance
PACS classification codes: 75.47GK; 75.47LX
Corresponding address: Department of Physics, University College of Science, Osmania University, Hyderabad 500 007, AP, India. Tel.: +91 40 27682242; fax: +91 40 27009002.