Date of Graduation

Fall 2020

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Robert Mayanovic

Keywords

heterostructure, magnetic, exchange bias, anisotropy, coercivity, hysteresis

Subject Categories

Nanoscience and Nanotechnology | Other Materials Science and Engineering

Abstract

A combination of thermal decomposition and surfactant-assisted synthesis route was utilized to synthesize novel CoO/MnFe2O4 heterostructured nanoparticles. Four samples of varying CoO core size were synthesized with variable extent of overgrowth phase. XRD, XPS, SEM and TEM data show evidence of MnFe2O4 spinel phase overgrowth on CoO rock-salt structured nanoparticles. XPS and magnetic data reveal partial oxidation and formation of Co3O4 phase on 7 nm and 19 nm size CoO-based nanoparticles. The remaining samples having 22 nm and 34 nm dimensions show a higher percentage of FiM materials overgrowth on the nanoparticle surface and no Co3O4 phase formation. The variation in core size, extent of MnFe2O4 overgrowth and Co3O4 formation significantly impacts the magnetic properties and exchange bias interactions of the heterostructured nanoparticles. The largest exchange bias of 6.2 KOe was measured from the 7 nm sized sample whereas largest coercivity of 3.26 KOe was measured from the 19 nm sized sample, at 5 K. Interface crystallinity, surface effect, uncompensated spins play a crucial role to achieve better exchange bias. The exchange bias showed sensitivity to core size and relative percentage of AFM and FiM materials. This effort in the synthesis technique of heterostructure core-shell system as well as understanding the large exchange bias effect may lead to the potential use of heterostructured nanoparticles in magnetic devices and biomedical applications.

Copyright

© Mohammad Tauhidul Islam

Available for download on Friday, December 01, 2023

Open Access

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