Date of Graduation

Summer 2022

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Kartik Ghosh

Abstract

In this thesis, detailed magnetic and electrical transport properties of composite thin films consisting of antiferromagnetic NiO, and ferromagnetic Ni have been studied. Highly oriented NiO thin films were grown on sapphire (0001) substrate using pulsed laser deposition with varying growth parameters such as oxygen pressure of the chamber and the substrate temperature. To obtain various percentage mixtures of Ni and NiO by means of introducing point defects (oxygen vacancies) into the NiO crystal structure, the as-grown films were annealed in forming gas (Ar:96% and H2:4%) at a fixed temperature of 600C and varying annealing time (0.5h to 6h). X-ray diffraction (XRD) data show that as-grown NiO film, which has a rock salt structure, is preferentially grown on the sapphire substrate along the (111) planes. The phase mixtures of Ni/NiO obtained by reduction annealing were confirmed by XRD, Raman spectroscopy, and scanning electron microscopy (SEM). In the XRD data, a very sharp peak at 44.4° indicates that Ni has a face-centered cubic (fcc) crystal structure. Detailed magnetic properties were investigated using a superconducting quantum interference device (SQUID) magnetometer. Temperature and field-dependent magnetization M (H, T) data show that pure NiO and Ni are antiferromagnetic and ferromagnetic, respectively. The NiO-rich samples also showed ferromagnetic behavior with a saturation magnetization of 3.8 x 10-5 emu, and coercivity of 270 Oe. Ferromagnetism (FM) has also been observed in Ni-rich samples in the ferromagnetic resonance (FMR) experiment, and the FMR linewidth increases with decreasing Ni phase in the composite thin films. Finally, density functional theory (DFT) calculation using quantum espresso was performed to understand the effect of oxygen vacancy on the electronic and magnetic properties of NiO. The behavior of the composite Ni/NiO thin films resembles a magnetic semiconductor which has a promising application in the arena of spintronic devices.

Keywords

pulsed laser deposition, epitaxy, antiferromagnetism, ferromagnetism, transport properties, ferromagnetic linewidth, density functional theory calculation

Subject Categories

Condensed Matter Physics

Copyright

© Bishwajite Karmakar

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