| Popis: |
In this thesis, the potential of all-spinel oxide tunnel junctions in the field of spintronics has been investigated. In particular, the suitability of the metallic and superconducting LiTi2O4 as non-magnetic electrode in an almost defect-free CoFe2O4-based spin-filter tunnel junction has been explored. For this purpose, high-quality spinel LiTi2O4 and CoFe2O4 thin films have been deposited by pulsed laser deposition on MgAl2O4 substrates. Both films were extensively characterised in terms of structural, surface, magnetic and transport properties. The LiTi2O4 showed metallic and superconducting properties, and the CoFe2O4 had insulating and ferromagnetic properties. A careful tuning of the different growth conditions of these oxides followed in order to grow CoFe2O4/LiTi2O4 bilayers in which LiTi2O4 maintains its metallic and superconducting properties and CoFe2O4 its insulating ferromagnetic characteristics. Transport measurements at low temperature have been carried out to explore details of the tunnelling in symmetric tunnel junctions of the form LiTi2O4/CoFe2O4/LiTi2O4. The measured current–voltage characteristics of these junctions revealed clear Josephson junction behaviour due to superconductivity of the LiTi2O4 electrodes. This conclusive evidence of the tunnel nature of these junctions proves that LiTi2O4 can be used as bottom electrode in all-spinel oxide tunnel junctions. |
