Date of Graduation

Summer 2020

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Robert Mayanovic

Keywords

Magnetic Heterostructured Nanocrystals, Hydrothermal, pH, Exchange Bias, Coercivity, Magnetic Domain, Spinel Structure, Magnetic Anisotropy, Interface, XPS

Subject Categories

Other Materials Science and Engineering

Abstract

The role of pH on the structural, morphological, and magnetic properties of hydrothermally synthesized NiO-based magnetic heterostructured nanocrystals (MHNCs) is investigated. The NiO nanocrystals were synthesized using a two-step thermal decomposition process whereas the deposition of the surrounding Mn-based phases was accomplished by hydrothermal means at pH values ranging from 2.4 to 7.0. The resulting heterostructured nanocrystals consist of inverted AFM-FiM NiO/±MnxNi1-xO/±Mn3O4 bimagnetic/trimagnetic systems. A complete characterization of the MHNCs was carried using XRD, TEM, EDS, MPMS magnetometry and XPS analysis. Structural investigations revealed predominantly faceted MHNCs ranging in size from 24-30 nm with expitaxially grown MnxNi1-xO overlayers and/or Mn3O4 decorated nanoislands. Magnetic data reveal a significant enhancement in the coercivity, exchange bias and remanent magnetization values with increasing pH values and peaking at a pH of ~5, followed by a substantial decline with further increasing pH. The XRD, TEM and magnetometry data are consistent with predominantly MnxNi1-xO shell formation at lower pH, mixed deposition of MnxNi1-xO shell and Mn3O4 islands at intermediate pH, and desposition of predominantly Mn3O4 islands at higher pH values. Finally, the XPS spectra analysis confirm Mn2+ incorporation at low pH values and an admixture of Mn2+ and Mn2+ at higher pH values in the MHNCs.

Copyright

© Abdullah Al Shafe

Available for download on Monday, August 01, 2022

Open Access

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