Prerequisites for high-quality magnetic tunnel junctions: XPS and NMR study of Co/Al bilayers

Aluminum films with thicknesses ranging from 1 nm to 12 nm have been sputte red on 20 nm thick Co layers. The properties of the Co/Al bilayers were stu died by X-ray photoemission spectroscopy (XPS) and spin-echo nuclear magnet ic resonance (NMR). Both methods show independently that a 1 nm Al film cov ers the Co surface completely. XPS and NMR also showed that layers thicker than 1 nm Al are not oxidized completely in ambient air. Similarities to an d deviations from niobium with Al overlayers (Nb/Al) are described. Prerequ isites for the fabrication of tunneling magnetoresistance devices based on Co or NiFe ferromagnets and an aluminum oxide barrier are discussed.