Structural, Transport and Magnetic Properties of Iron and Magnesium Oxide Thin Films.
The structural, electrical and magnetic properties of Fe and MgO thin films are investigated. The Fe films are fabricated using molecular beam epitaxy (MBE) on MgO(001) and MgO films on Fe(001). They are characterized by surface structural probes including reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD). They also are studied by the surface magneto-optic Kerr effect (SMOKE) and other magnetic probes. Computational simulations of the XPD are explored as well. The initial growth mode of Fe films on MgO is not layer-by-layer, while MgO films grow in flat, epitaxial layers on Fe. An XPD study of the MgO substrate shows that the arrangement and type of atoms surrounding the electron emitters are the most important factors in XPD intensity determinations. It also is concluded that multiple scattering attenuation is more pronounced along the atomic chains with a larger interatomic spacing. Electrical transport measurements of the Fe films show a crossover from a two dimensional disordered regime to a three-dimensional metallic one as a function of temperature. The parameters extracted from the transport data are consistent with previous studies and are well explained by standard transport theory in disordered materials. SMOKE experiments show that no ferromagnetic signal is detectable below 4 ML thickness of Fe. The inability to detect long-range ferromagnetic order in the thin limit is attributed to the effect of growth morphology. Superparamagnetic behavior is investigated in 10-ML Fe films grown at 700 K. Magnetization data taken at 300 K was fitted to a Langevin function to yield an average particle diameter of ~ 70 A. The time dependent remanent magnetization shows non-exponential decay caused either by the distribution in particle size or by interactions among particles. Uniaxial in-plane magnetic anisotropy is observed in 10-ML Fe films grown on MgO(001) at room temperature via oblique-incidence MBE. The anisotropy correlates with a pronounced asymmetry observed in XPD polar scans. Both quantities are believed to be caused by a directed surface roughness morphology that develops due to the novel deposition process.
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- Physics: Condensed Matter; Engineering: Materials Science