8-9th August, 2008 School of Materials Science & Nanotechnology,Jadavpur University
Effect of nanometric grain size on electronic– and magneto-transport properties of Nd0.7-xGdxSr0.3MnO3 (x = 0, 0.1, 0.2 and 0.3)
S. Kundu and T. K. Nath*
Department of Physics and Meteorology
Indian Institute of Technology Kharagpur
Kharagpur 721302, INDIA
* Email: tnath@phy.iitkgp.ernet.in
The compounds with general formula R (1-x) AxMnO3 (R=La, Nd, Pr etc. A= Ca or Sr ) are known to the physicists since last few decades because of their colossal magneto-resistive (CMR) property, complicated electronic structure, phase separation and many other unusual electronic and magnetic behaviors which are outcome of the correlation between lattice, charge, spin and orbital degrees of freedom existing in such rare earth manganites. One member of this doped manganites family Nd0.7Sr0.3MnO3 with intermediate bandwidth shows ferromagnetism and CMR property around this particular level of doping. In this present investigation we have taken the system Nd0.7-xGdxSr0.3MnO3 (x=0, 0.1, 0.2, 0.3) formed by substituting Nd by Gd which has much smaller ionic radius than Nd and very high magnetic moment. The samples have been synthesized by chemical “pyrophoric” reaction route. The as-prepared samples have been sintered at high temperature (1150 OC) to produce the bulk series of samples whereas the same have been sintered at low temperature (750 OC) to get the samples with nanometer size grains. We have confirmed the single phase of the samples by their XRD micrographs. The grain size of the nanometric samples has been estimated to be 26 nm by using Debye Scherer formula. The HRTEM and FESEM images of the samples also confirm the nanometric size of the grains. We have performed the resistivity and ac susceptibility measurement of the samples down to 78 K. Both the values of TP (metal - insulator transition temperature) and TC (ferromagnetic to paramagnetic transition temperature) for these nanometric samples are found to be less than that obtained in their bulk counterparts. We have also found that both TP and TC gradually decrease with increasing substitution of Gd in the nanometric as well as in the bulk samples. The high resolution magneto-resistance (MR) measurements of all the samples have been carried out in the low field (< 5000 Oe) region. We have used theoretical model to analyze our MR vs. H data at several temperatures down to 77 K. The contribution from spin polarized tunneling MR and the intrinsic MR have been separated out for detail investigations of the low field magneto-resistance (LFMR) of those samples.
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