Growth, magnetic, and transport properties of magnetic superlattices.

Three series of epitaxial magnetic superlattices are grown on GaAs substrates: cobalt-gold, cobalt-copper, and cobalt-chromium. The interrelationship between crystal microstructure, magnetic, and magnetotransport properties is explored with reflection high-energy electron diffraction (RHEED), magnetometry, Hall effect, and magnetoresistance. Perpendicular anisotropy is observed in the cobalt-gold and cobalt-copper superlattices with cobalt thickness less than 18A and 9A, respectively. This anisotropy is found to significantly enhance magnetoresistance at cryogenic temperatures. A calculation of the magnetoelastic anisotropy due to epitaxial strain is presented, and when added to the magnetocrystalline and shape anisotropies, quantitatively accounts for the experimental data. In the cobalt-chromium superlattices a structural transition in the chromium layers from close-packed to body centered cubic in the Kurdjumov-Sachs and Nishiyama-Wasserman orientations is observed in real-time with a charge coupled device RHEED detection system.