Epitaxial growth and characterization of multifunctional heterostructures: Integrating ferromagnets, ferroelectrics, insulators and III-V semiconductors

The integration of ferromagnetic metals and alloys with metal oxides and vice versa can be of importance for the formation of multifunctional material heterostructure and can lead to novel device applications. This research examines the effect of epitaxial growth condition on the structural, morphological, chemical and magnetic properties of the ferromagnetic films of Fe and Co2MnGe on metal oxides surfaces of (Sr,Ba)TiO3, and MgO (001).; The substrate temperature during the molecular beam epitaxy growth of Fe and Co2MnGe films on SrTiO3 and BaTiO3/SrTiO 3 (001) surfaces and Co2MnGe films on MgO (001) affects the extent of 3-D island growth mode. The enhancement of magnetic coercivity with higher growth temperatures was correlated to the domain wall pinning at the island edges.; Co2MnGe grows in a new relaxed tetragonal phase at low growth temperatures and in the expected cubic structure at higher growth temperatures. The low temperature tetragonal phase, in contrast with the high temperature cubic phase, has induced perpendicular magnetocrystalline anisotropy. The crystal quality and atomic ordering in the Co2MnGe films improve with higher growth temperatures. The atomic disorder was found to introduce in-plane magnetic anisotropy. Co2MnGe was found to be thermally stable to higher temperatures on MgO (600°C) as compared to 350°C on SrTiO3 and 450°C on BaTiO3. A two-step growth mode not only improved the crystallinity, atomic ordering and surface roughness of the Co2MnGe films but also helped avoid interfacial reactions with the substrates.; The epitaxial ME heterostructure in the reverse form, BaTiO3/Fe/GaAs (001) was achieved by using a 20ML-thick diffusion barrier layer of Sc 0.3Er0.7As in between Fe and GaAs substrates; and a 700A-thick oxidation barrier layer of MgO between BaTiO3 and Fe.; The epitaxial Fe/BaTiO3 (001) heterostructure was investigated for the lattice coupling. The magnetization and magnetic anisotropy of Fe were dynamically changed by the structural changes in the underlying BaTiO 3 lattice. It was observed that the induced change in magnetization scales with the Fe film thickness and extrapolates to the zero value for the zero film thickness showing the stronger influence of the volume strain rather that the interface electronic effects.