Date of Graduation

Spring 2019

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Robert Mayanovic

Keywords

core-shell nanoparticles, coercivity, exchange bias effect, oxidation state, thermal decomposition, hydrothermal epitaxy

Abstract

The doping concentration (Mn concentration) dependent magnetic properties of NiO@NixMn1-xO novel inverted core-shell magnetic nanoparticles are of great interest of this present research. Primarily, we investigated the oxidation state of Ni from size-dependent four NiO NPs samples, and then studied the variation in the magnetic properties of Mn concentration-dependent NiO@NixMn1-xO CNPs. The NiO nanoparticles were synthesized using a thermal decomposition method. The XRD data indicates that the crystal structure (rock salt) remains fixed in all NiO samples and XPS data shows the oxidation state of size-dependent NiO nanoparticles is 2+. The hydrothermal epitaxy method was used to incorporate Mn in NiO crystal. The resultant product is comprised of antiferromagnetic core (NiO) and ferro/ferrimagnetic shell (NixMn1-xO). The XRD data showed that the crystal structure is identical in both NiO NPs and NiO@NixMn1-xO CNPs and the varying concentrations of Mn have not altered the crystal structure. The XPS analysis indicates the oxidation state of both Mn and Ni is 2+ and the survey scan shows the presence of all constituent elements. The SQUID magnetometer measurements provide us both the ZFC and FC hysteresis loop and indicate the horizontal shift of the FC hysteresis loop in the negative axis of the applied magnetic field which is called exchange bias. The magnetic data shows both the coercivity and the exchange bias of concentration-dependent NiO@NixMn1-xO CNPs are maximum for 0.08 M manganese. The lower resolution TEM image shows most of the CNPs are faceted and some of them are pseudospherical. The HRTEM image gave a clear visualization of the core, shell, and interface region.

Copyright

© Md Nazmul Alam

Open Access

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