We have performed composition depth profiles and other structural experimen
ts on Gd/Co multilayers and bilayers. Analysis of Auger depth profiles indi
cates a strongly asymmetric diffusion, especially of Co into the Gd layers.
In multilayers, it is found that Co diffuses throughout the Gd layers and
forms a Gd1-xCox amorphous alloy (x = 0.29-0.35) that is limited at nearly
the eutectic composition (x = 0.37). Therefore, if the Co layers are nomina
lly not too thin (greater than or similar to 3 nm), the multilayer mainly c
omprises an amorphous layers of composition around Gd0.7Co0.3 and layers of
pure Co. Thin Co layers (3-7 nm) present broad halos in x-ray diffraction
scans at wave vectors characteristics of pure cobalt. Thick layers (greater
than or similar to 10 nm) show crystalline peaks with a coherence size (xi
(perpendicular to)) shorter than its own layer thickness, suggesting the ex
istence of amorphous phases next to the interface. This can be explained by
the growth of pure and amorphous Co up to a thickness of 2-4 nm on the amo
rphous Gd alloy seed, but further Co deposition consists of hcp crystalline
grains. (C) 2000 American Institute of Physics. [S0021-8979(00)02505-6].