Stabilisation of fcc cobalt layers by 0.4 nm thick manganese layers in Co/Mn superlattices

Epitaxial Co/Mn multilayers (0.75 to 6 nm Co, 0.4 nm Mn layer thickness) ha ve been grown on mica substrates covered by a (0002) Ru buffer layer. The s tructural properties of these layers have been studied using X-ray diffract ion, nuclear magnetic resonance (NMR), and high resolution transmission ele ctron microscopy (HRTEM). The Co layers, grown as face centred cubic (fcc), were found to be stabilised by the very thin Mn layers. Data obtained usin g X-ray diffraction and NMR were analysed and found to be in good agreement , while Monte-Carlo simulations were used to interpret the data and calcula te the expected diffracted intensity and NMR spectra. The HRTEM data show t hat the Mn layers give rise to a large strain contrast extending, in the gr owth direction, over a distance which exceeds the thickness of the Mn layer s. The superlattices could be described as having an fee structure containi ng randomly located stacking faults with varying densities. The results ver ify the presence of a dominant, almost perfect phase of fee stacking, and o f a faulted hcp phase, while the number of defects increases with the Co la yer thickness.