Cu top layer diffusion was used to reduce the exchange coupling of FePt magnetic grains since diffusion along grain boundaries is easier than bulk diffusion. After the deposition of 2 and 4 rim Cu layer on FePt film at 350 degrees C the slope of the out-of-plane M-H loops decreased and the out-of-plane coercivity increased from 3158 Oe to 6050 Oe, suggesting the exchange coupling decreases. The magnetisation reversal mechanism changed from the domain wall motion to the rotation mode with the deposition of Cu top layers. Moment decay measurements based on the Sharrock formula were made to evaluate the thermal stability factor KuV*/k(B)T and the magnetic switching volume V*.V* was reduced by increased Cu top layer which further confirmed the reduction of exchange coupling. (c) 2005 Elsevier B.V. All rights reserved.