Interfacial characteristics and magnetoresistive properties of reactively sputtered Fe-Al²O³-Co magnetic tunnel junctions

Abstract

Magnetic tunnel junctions (MTJs) comprised of two magnetic metal layers separated by a thin insulating oxide layer have been prepared by rf sputtering onto thermally oxidized (100) silicon wafers at room temperature. The magnetic layers with thickness of ~50 nm consisted of thin films of Fe and Co, and the material for the oxide barriers with thickness of ~10 nm was A1_,O₃. The barriers were prepared by rf reactive sputtering from pure metallic Al sources in mixed argon-oxygen atmospheres. Pt/Al₂O₃/Pt tunnel junctions were also prepared to characterize the reactively sputtered Al₂O₃ barriers. Auger electron spectroscopy was used in this study to characterize the interfacial structures of the junctions. A distinct nonlinear transport behavior, even at 300 K, in Pt/Al₂O₃/Pt junctions has revealed that the reactively sputtered A1₂O₃ is a good barrier material for tunnel junctions. Magnetoresistive measurements were made perpendicular to the film plane on the MTJs for in-plane applied magnetic fields and the results were discussed in connection with the interfacial structures of the MTJs.