| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系 === 102 === The aim of this work was to fabricate an all-oxide spin valve using multiferroic BiFeO3 as the antiferromagnetic pinning layer. The proposed architecture was Zn0.7Ni0.3Fe2O4/ LaNiO3/ Zn0.7Ni0.3Fe2O4/ BiFeO3/ LaNiO3/ SrTiO3. We have grown such a multilayered heterostructure epitaxially by the RF magnetron sputtering. X-ray diffraction showed that the films were indeed biaxially aligned with reasonable in-plane and out-of-plane textures, under the growth conditions optimised for achieving good ferroelectric and magnetic properties. Some key physical and material issues for building up such a novel device were addressed, in particular the heteroepitaxy-induced strain effects on the electrical and magnetic properties of each layer and the establishment of exchange bias between BiFeO3 and Zn0.7Ni0.3Fe2O4. The strains caused a significant increase in the coercivity but a decrease in the saturation magnetization of the ferrimagnet used. The all-oxide architecture allowed the spin valve to be field-annealed from a temperature above the Neel point of BFO (380 OC), after which a clear exchange bias was observed. Magnetoresistance was also achieved in such all-oxide spin valves, which was switchable magnetically in a similar way as the conventional metallic spin valves.
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