Advisor(s)

Vincent G. Harris

Contributor(s)

Vittoria Carmine, Katherine S. Ziemer

Date of Award

2008

Date Accepted

12-2008

Degree Grantor

Northeastern University

Degree Level

M.S.

Degree Name

Master of Science

Department or Academic Unit

College of Engineering. Department of Electrical and Computer Engineering.

Keywords

Engineering, Magnetic properties, Nickel ferrite films

Subject Categories

Ferromagnetism

Disciplines

Engineering

Abstract

Series of heteroepitaxy spinel ferrite thin films (NixFe3-xO4) were prepared by the alternating target laser ablation deposition (ATLAD) technique. Different from conventional pulsed laser ablation deposition (PLD), the AT-LAD technique allows different laser pulses incident upon multiple targets alternatively to grow the film in an atomic layer-by-layer fashion. In this research, targets of NiO and Fe2O3 were used to grow NixFe3-xO4 films on single crystal MgO (111) substrates. The substrate temperature and oxygen pressure were fixed at 900C and 5 mTorr, respectively. Values of x were varied by changing the number of laser pulses on NiO and Fe2O3 targets within each cycle. NixFe3-xO4 films, with spinel structure oriented along <111> direction, were characterized by CuK_alpha x-ray diffraction (XRD). The maximum lattice parameter (8.353 A) was obtained at a laser shot ratio Fe:Ni~2 which is also larger than the bulk value (8.339 A) [2]. We studied the surface and cross-section morphology using scanning electron microscope (SEM). The SEM images revealed triangle shaped grains oriented along the substrate orientation, the <111> direction. Energy dispersive x-ray analysis (EDAX) was utilized to identify the atomic ratios of Ni and Fe elements. It is revealed Fe:Ni is close to 2 when the laser pulses on NiO and Fe2O3 target were 5 and10 per ATLAD cycle, respectively. The saturation magnetization, was 4piMs, of the NiFe2O4 thin films, measured by vibrating sample magnetometer (VSM), ~4,000G, which is larger than the bulk value (~3,400G)[12]. Microwave properties were measured using a ferromagnetic resonance (FMR) spectrometer. Using the Smit & Beljar FMR equations[9], the minimum anisotropy constants, K_perp= -238700 (erg/cm^3), obtained corresponding to an atomic ratio Fe:Ni~2. The maximal FMR linewidth, deltaH=1061(Oe), was also obtained from this film. The corresponding effective gyromagnetic factor (g_eff) is 2.00, which is obtained using the plot of f as a function of Hi. We calculated the cation distribution based on EDAX determined atomic ratio (Fe:Ni) and the measured 4piMs. This information can also be confirmed by synchrotron based x-ray absorption spectra analysis. The results indicated more Ni ions on A sites in ATLAD films compared with bulk. This explains the expanded lattice parameter and the increase of 4piMs.

Document Type

Master's Thesis

Rights Holder

Huiching Chang


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