Magnetic Tunnel Junction Co / Cu / Co Sandwich Giant Magnetoresistance Effect

In this thesis, we investigated the fabrication method and magnetoresistance (MR) effectof ferromagnetic tunnel Junctions which consisted of Co and NiFe separated by a thin insulator,and we also studied the magnetoresistance effect of Co/Cu/Co sandwiches with Fe, Ti, Cucapping layers and Fe, Cr buffer layers at room and low temperature At the same time, magneticproperties of above samples were also measured at much lower temperature (above 5K)The Co and NiFe layers in hanel Junctions of Co-Insulator-NiFe were evaporateddirectly using a UHV electron beam evaporation, while the Insulator layer was fabricated byevaporation using Al and Al₂:O₃ as source targets followed by oxidization process in airExperiment results demonstrated that the quality of the insulator layer and thus the tunnelJunctions could be improved when the evaporated Al₂O₃ layers were oxidized at a proper highertemperature We has successfully attained Co-Insulator-NiFe tunnel Junctions which showtunneling effect, and its max MR value at room temperature is about 0.7% In addition, possiblemethods to improve the quality of the samples and to fabricate ferromagnetic tunnel Junctionsusing planar circuit processing techniques were discussed respectivelyCo/Cu/Co sandwiches with Fe, Ti and Cu capping layers were also fabricated by UHVelectron beam evaporation It has been found that the coercivity and saturation field of thesamples with Fe capping layers were obviously reduced, though the MR values of Co/Cu/Cosandwiches with Fe, Ti and Cu capping layers show no great change at room temperature Withtemperature decreasing, the capping layers strongly enhanced the MR values of Co/Cu/Cosandwich At 77K, MR values of Co/Cu/Co sandwiches with Fe, Ti, Cu capping layers were9.9%, 9.0%, and 7.7% respectively while MR value for the sample without capping layer wasonly 6.8% All the results suggested that the giant magnetoresistance in Co/Cu/Co sandwich wasstrongly influenced by capping layer and the interface between up magnetic Co layer and thecapping layerAs for the Co/Cu/Co sandwiches with Fe buffer layers, the coercivity of the samples(25.2Oe) was far smaller than that of Co/Cu/Co sandwiches with Cr buffer layer (98.3Oe), andthe sensitivity of the corresponding sandwiches was accordingly greatly enhanced to 0.3%/Oe atroom temperature We found that the MR value was the largest when the thickness of Fe bufferlayer was 7nm Compared with Co/Cu/Co sandwiches with Cr buffer layer, MR values of the Febuffered samples were much strongly influenced by temperafore The asymmetry of MR curvesof the Fe buffered samples were obviously seen at 77K Temperature dependence measurementof the magnetization of the samples showed that it may be caused by the antiferromagnetic stateof fcc Fe buffer layer at low temperature...