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

Journal Article · Thu May 07 00:00:00 EDT 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4919418· OSTI ID:22402991

Chatterjee, Soumi ^[1]; Maiti, Ramaprasad ^[1]; Saha, Shyamal Kumar; Chakravorty, Dipankar ^[2]

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1. MLS Professor's Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata 700032 (India)
2. Department of Materials Science, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata 700032 (India)

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 a 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.

• OSTI ID: 22402991
• Journal Information: Journal of Applied Physics, Vol. 117, Issue 17; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

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