| We have investigated spin-dependent transport in magnetic tunnel junctions based on ferromagnetic oxides. Three types of junctions were fabricated from thin trilayer films that were grown on different substrates using both new and conventional growth techniques. Typical colossal magnetoresistance (CMR) oxide, La0.67Sr0.33MnO3 and 4d-based ferromagnetic oxide, SrRuO3 were explored as electrode materials. Magnetotransport on the junction systems was systematically conducted by varying device size and configuration, temperature, bias voltage, and direction of applied field. The transport properties were compared with previous reports and analyzed in parallel with microscopy study.; Off-axis sputtering, a relatively new method for the oxide growth enabled smoother surfaces and more uniform barrier interfaces in manganite homo-trilayers. We obtained highly symmetric and well-defined magnetoresistive behaviors for the manganite junctions. Large MR was achieved in a small magnetic field of about 80 Oe. For the first time in oxide junction systems, scaling has been finely done over junction areas and barrier thicknesses. Surprisingly, MR was sustained to near room temperature, representing the highest temperature ever reported in the manganite junction systems.; Ruthenate-incorporating junctions were tried for the first time. We found a small MR of 2.7% for a ruthenate homo-junction through a Tesla-range field scan. We also obtained an inverse MR of −16% for a manganite-ruthenate hetero-junction, corresponding to the negative spin polarization of −9% at EF for SrRuO3. The observation is the manifestation of the existence of a negatively polarized material at the Fermi level, and also a proof of the general applicability of Julliere model. However, the ruthenate-involving junctions showed worse barrier interface uniformity and potential interfacial compound formation. Therefore, poor area and barrier thickness scalings and heavy bias dependence of magnetotransport resulted from the junctions, particularly, ruthenate homo-junctions. These results on oxide-based junctions indicate that the interface uniformity is a critical factor for determining junction performance. |
