Interdiffusion up to the eutectic composition and vitrification in Gd/Co multilayers

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].