Giant magnetoresistance and magnetic coupling in cobalt/copper superlattices investigated by the magneto-optical Kerr effect.

摘要

The giant magnetoresistance (GMR) effect arising from the oscillatory interlayer exchange coupling across non-magnetic spacer layers in a wide variety of ferromagnetic transition metal multilayers (superlattices) has attracted strong attention from both the fundamental and application viewpoint since its discovery. GMR and magnetic coupling in Co/Cu superlattices grown in a dual-beam electron evaporation chamber have been investigated by using the combined three-axis magneto-optical Kerr effect (MOKE), magnetotransport measurements, X-Ray Diffraction, Rutherford Backscattering (RBS), Transmission Electron Microscope (TEM), and domain observation with STEM Electron Holography.; A series of pure Co thin films and multilayers (Co(t{dollar}sb{lcub}rm Co{rcub}{dollar})/Cu(t{dollar}sb{lcub}rm Cu{rcub}{dollar})) {dollar}sb{lcub}rm n{rcub}{dollar} (n is bilayer number) have been evaporated on Si(100) oriented crystals, Corning cover glass slides, and holey carbon film covered grids at room temperature. X-ray diffraction and TEM measurements indicate that the pure Co thin films have polycrystalline structure composed of crystallites ranging from 2-5 nm with fcc (111) and hcp {dollar}{lcub}1010{rcub}{dollar} and {dollar}{lcub}0002{rcub}{dollar} orientations. Hysteresis loop measurements from MOKE and domain observations with STEM holography show all films, including the thinnest film (2 nm) are ferromagnetic with in-plane anisotropy. Films between 4 nm and 50 nm have in-plane four-fold anisotropy. The anisotropy magnetoresistance (AMR) of the films increases with thickness with a maximum value 1.5% at the thickness of 50 nm, then decreases towards the bulk value 0.5%. The information obtained in the pure Co films is useful in studying GMR Co/Cu superlattices.; Large Angle X-ray Scattering (LAXS) data and TEM images indicate that the series of (Co(1.5nm)/Cu(t{dollar}sb{lcub}rm Cu{rcub}{dollar})) {dollar}sb{lcub}rm n{rcub}{dollar} ({dollar}rm 6