Date of Graduation

Fall 2017

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Robert Mayanovic

Abstract

The synthesis along with the structural and magnetic properties of manganese (Mn) and cobalt (Co) -incorporated nickel oxide (NiO) inverted core-shell nanoparticles (CSNs) were investigated. The primary objective of this study was to determine the effect of substitution of nickel (Ni) by transition metal ions (Mn2+/Co2+) in affecting the magnetic properties of the resultant CSNs. The core of the CSNs is comprised of NiO and the shell constitutes a Nix(Mn/Co)1-xO phase. The synthesis of the CSNs was accomplished in two steps: first, NiO nanoparticles were synthesized using a thermal decomposition method. In the second step, our hydrothermal nanophase epitaxy method was used to create the core-shell structure. Rietveld refinement of X-ray diffraction (XRD) data show rock salt structure throughout in the Mn/Co incorporated CSNs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show a combination of pseudo-spherical and faceted shapes of CSNs whereas energy dispersive spectroscopy (EDS) indicates transition metal incorporation in the CSNs. The high-resolution (HR) TEM images confirmed the formation of distinct core and shell regions. Magnetic characterization shows that the Mn- and Co-substituted nickel oxide-based CSNs possess an inverted magnetic structure, with an antiferromagnetic core and a ferro- or ferrimagnetic shell. The coercivity and exchange bias properties are of larger magnitude in Mn-incorporated than in Co-incorporated CSNs.

Keywords

core-shell nanoparticles, magnetic, exchange bias, hysteresis, coercivity

Subject Categories

Nanoscience and Nanotechnology | Other Materials Science and Engineering

Copyright

© Samiul Hasan

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