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Title: Enhancement of electrical conductivity in CoO-SiO{sub 2} nanoglasses and large magnetodielectric effect in ZnO-nanoglass composites

Nanoglasses of compositions xCoO·(100-x)SiO{sub 2} (mol. %) with x having values 10, 15, and 20, respectively, were grown within the nanopores of a pellet comprising of ZnO nanoparticles by soaking the latter in a suitable sol followed by necessary heat treatment. Both Co{sup 2+} and Co{sup 3+} ions were present and confirmed by X-ray photoelectron spectroscopy, the fraction of Co{sup 2+} species being ∼ 0.70. Small polaron hopping conduction was found to be present in the nanoglasses. The activation energy in the latter was observed to be smaller (range of 0.32–0.44 eV) than that in the corresponding bulk glass (0.70–0.77 eV). This was caused by the higher free volume in the nanoglass as compared to that of the bulk glass. This was confirmed by the extracted values of intersite separation between cobalt ions, which were higher in the nanoglass. Weak ferromagnetism was exhibited by the nanocomposites. This was ascribed to super exchange interaction between spin moments associated with Co{sup 2+} and Co{sup 3+} ions, respectively, leading to an antiferromagnetic spin alignment. The nanocomposites showed magnetodielectric effect with the magnetodielectric parameter having values in the range of 5.5% to 10%. The experimental data were fitted to equations derived from Catalan's model by invoking amore » negative and a positive magnetoresistance for nanoglasses of compositions having x = 20 and x = 10, respectively. A weak spin-orbit coupling and wave function shrinkage in a magnetic field for strongly localized states, respectively, are believed to cause such behaviour in the nanoglass systems concerned. Direct magnetoresistance measurements were carried out on the nanocomposites containing nanoglasses having 10CoO and 20CoO, respectively. The trend of results obtained indeed confirmed the presence of positive and negative magnetoresistance in the two nanoglasses, respectively. The materials would be suitable for magnetic sensor applications.« less
Authors:
 [1] ;  [2] ;  [1] ; ;  [3]
  1. MLS Professor's Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata 700032 (India)
  2. (India)
  3. Department of Materials Science, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata 700032 (India)
Publication Date:
OSTI Identifier:
22402991
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 17; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ACTIVATION ENERGY; ANTIFERROMAGNETISM; COBALT IONS; COBALT OXIDES; COMPARATIVE EVALUATIONS; EV RANGE; EXCHANGE INTERACTIONS; FERROMAGNETISM; HEAT TREATMENTS; L-S COUPLING; MAGNETIC FIELDS; MAGNETORESISTANCE; NANOCOMPOSITES; NANOPARTICLES; SILICON OXIDES; X-RAY PHOTOELECTRON SPECTROSCOPY; ZINC OXIDES