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Abstract
A detailed structural, magnetic and physics properties of La1−xMnO3±δ (LMO) nanomanganites were investigated to find out the role of cationic vacancies (La vacancy with Mn3+/Mn4+) in grain size modulation. Crystal structure and phase analysis of all samples were carried out by Rietveld refinement of high-resolution XRD and neutron diffraction data. We report here, the oxygen content in studied LMO compound decreases with increase in La vacancies in parent site and a parasitic Mn3O4 phase has been evolved in the range of 0.9 ≥ La/Mn ≥ 0.7. Para to ferro magnetic transition temperature (TC) of all nanometric samples (La/Mn < 0.9) was found at high temperature side (≥260 K) whereas, the same for bulk one (La/Mn ≥ 0.9) was around 160 K. The enhancement of TC (~70 K) with size reduction is attributed to broadening of bandwidth due to compaction of MnO6 octahedra in system unit cell. In bulk sample, a secondary cluster/spin glassy phase is found below 50 K, whereas the glassy phase has been suppressed in nanoscale. Field-dependent magneto-resistance measurements are also carried out for all samples at different temperatures to get a profound insight of magneto-transport dynamics of the present system.
Acknowledgements
This research work was supported by CSIR through award No. 09/081(1077)/2010-EMR-I. PTD is thankful to the Central Research Facility, IIT Kharagpur, UGC-DAE, Indore for various experimental facilities. We acknowledge Dr. R. Rawat and Mr. Pallab Bag for their valuable contribution in the manuscript and Sp. heat measurements. PTD also would like to thank D.K. Pradhan, University of Puerto Rico, U.S.A. for performing the XRF measurements.