Structural properties of Co/Au superlattices investigated by high-resolution transmission electron microscopy

Abstract

Ion-beam-sputtered and electron-beam-evaporated Co/Au multilayers have been investigated with high-resolution transmission electron microscopy. The multilayers are found to exhibit a strong {111} texture and to contain Co predominantly in the cubic (fcc) phase. Misfit dislocations were directly observed and found to be located near the Co/Au interfaces. Structural features correlate with the magnetic anisotropy. Large crystalline units (vertical columns with ∼50 nm diameter reaching throughout the superlattice) are composed of small regions, a few nanometers in size (nanocrystallites), which are tilted towards each other by a few degrees. The microstructure of the large units remains unchanged for all investigated samples. The average size of the nanocrystallites and their mutual tilting angle vary systematically and are obviously correlated to the magnetic anisotropy. A high-crystalline quality (large nanocrystallites and small tilt angles) increases the value of the magnetic anisotropy constant Keffu. This behavior is unique for the presently investigated Co/Au multilayers independent of the fabrication technique. Moreover, these magnetostructural correlations may as well be valid for other magnetic/nonmagnetic metal superlattices.