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

The structure of the Co layer in sputter-deposited Ta/Cu/Co/Cu/Ta sandwiches has been investigated before and after vacuum annealing up to 280 degrees C by cross-sectional high-resolution TEM. The as-deposited sandwiches show a strong [111] fee texture with, in a number of places, many hcp stacking faults distributed all over the 75 Angstrom-thick Co layer. After annealing, the stacking faults present in a region about 20 Angstrom thick from each Co/Cu interface rearrange, leaving behind a plain Co fee structure. Relaxation of strain due to lattice mismatch at the Co/Cu interfaces is believed to contribute to the transformation of hcp into fee stacking sequences during annealing below the martensitic transition temperature.