Abstract
The present research focused on the fabrication of sandwiched nanostructure of pseudo-spin valve via the atomic layer deposition process. The structures of the three layer thin films included Si(100)/FM1/Au/FM2. The FM1 and FM2 were nano-thin films of ferrimagnetic iron oxide and we fixed the thicknesses of the FM1 and Au thin films but varied the thickness of the FM2 iron oxide thin film. Since iron oxide thin films prepared at low temperatures via the atomic layer deposition process were amorphous, the structure was heat treated with hydrogen gas (H2) in reduced pressure environment, to reduce the amorphous iron oxide to crystalline Fe3O4. The resulting structures were then studied for the relevant magnetic characteristics subject to variations in thickness of FM2 and application of the reductive heat treatment process. The surface morphology of the oxide thin films was observed and characterized with SEM and AFM. Amorphous iron oxide thin films were transformed into ferrimagnetic Fe3O4 crystal films via reductive heat treatment in hydrogen atmosphere. The crystalline structures of the reduced thin films were confirmed with XRD and XPS. For magnetic measurements, hysteresis curves and magneto-resistances were measured with the vibrating sample magnetometer (VSM) and 4-point probe in an applied magnetic field, respectively. From the results of SEM and AFM, the surface roughness of the iron oxide thin films increased significantly due to growth and aggregation of Fe3O4 crystals after the reductive heat treatment. And from the results of XRD and XPS, the amorphous iron oxide was successfully reduced to Fe3O4 crystals with the reductive heat treatment. Before the reductive heat treatment, the iron oxide films were amorphous, the corresponding net magnetization was equal to zero and no hysteresis was observed. But after the reductive heat treatment, the iron oxide was transformed into Fe3O4 crystals and showed hysteresis phenomena. As to the magneto-resistance, the pseudo-spin valve structures before and after the reductive heat treatment both showed magneto-resistances. And with increasing of deposition cycle numbers of the second layer iron oxide, magneto-resistance values all have the tendency of increase.