Annealing effect of copper on the cobalt structure in Cu/Co/Cu sandwiches

The structure of the cobalt layer in sputter-deposited Ta/Cu/Co/Cu /Ta sandwiches has been investigated before and after vacuum annealing up to 280 deg C by cross-sectional high-resolution TEM. The as-deposited sandwiches show a strong < 111 > fcc texture with, in a number of places, many hcp stacking faults distributed all over the 75A-thick Co layer. After annealing, the stacking faults present in a region approx20A thick from each Co/Cu interface rearrange, leaving behind a plain Co fcc structure. Relaxation of strain due to lattice mismatch at the Co/Cu interfaces is believed to contribute to the transformation of hcp into fcc stacking sequences during annealing below the martensitic transition temperature.