Date of Graduation

Summer 2017

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Robert Mayanovic

Keywords

Hydothermal nanophase epitaxy, alpha chromium oxide, core shell nanoparticles, room temperature ferri-magnetism, magnetic nano particles, exchange bias, coercivity, HR-TEM, XPS, two step synthesis route, hydrothermal treatment

Subject Categories

Other Materials Science and Engineering

Abstract

The structural and magnetic properties of copper (Cu) and aluminum (Al) -incorporated chromium oxide (α-Cr2O3, i.e., chromia) inverted core-shell nanoparticles (CSNs) were investigated. The objectives of this study were to determine the role of the substituting (for chromium, Cr) element and of Cu concentration on governing the magnetic properties of the CSNs. For synthesis of the CSNs, α-Cr2O3 nanoparticles were first grown using microwave assisted synthesis whereupon a hydrothermal nanophase epitaxy (HNE) method was used to incorporate Cu or Al in the chromia-based shell of the nanoparticles. The morphology, structure and size characteristics of the CSNs were determined using transmission emission microscopy (TEM) and x-ray diffraction (XRD). Rietveld refinement of the XRD data confirms continuation of corundum type structure throughout both core and shell. The high resolution (HR) TEM images confirmed the formation of distinct core and shell regions. The analysis of HR XPS (High resolution X-ray photoelectron spectroscopy) data confirmed the oxidation states of Cr, Cu and Al to be 3+, 2+ and 3+ respectively. Magnetic characterization shows that the Cu- and Al-substituted chromia-based CSNs of comparable concentration exhibit AFM-FM/FiM and predominantly AFM magnetic properties, respectively. The exchange bias properties were found to be optimized at a concentration of 3.92 atomic percentages (at%) in relation to lower and higher at% Cu substitution in the chromia-based CSNs.

Copyright

© Tamzid Ibn Minhaj

Available for download on Friday, May 31, 2019

Open Access

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