The measured activation energy is thus the sum of the vacancy formation energy and the Co vacancy exchange barrier. Assuming a value of 0.474 eV for the vacancy formation energy [15], we obtain a value of 0.44 eV for the Co vacancy exchange barrier. From this we conclude that the effective repulsive interaction must be somewhat smaller than what was found for Pd, as the exchange barrier tends to be closer to the diffusion barrier for a vacancy in clean Cu. To quantitatively verify the value of the interaction energy that we obtained, we now compare our experimental results with numerical calculations.