  L10 (CuAu(I)-type) ordered FePd as well as FePt and CoPt, due to their high
magnetic anisotropy, are candidate materials for future ultra-high density
magnetic recording. Atomic diffusion governs the structural relaxation and
associated changes in the physical and magnetic properties in these alloys.
Such processes involve diffusion paths of a few angstroms. In developing modern
storage devices it is indispensable to understand these processes. Neutron
reflectometry (NR) and Synchrotron M\"ossbauer Reflectometry (SMR) are suitable
non destructive methods to study self-diffusion in a chemically homogenous
isotope multilayer with diffusion lengths of the order of a few angstroms. From
the diffusion parameters obtained from NR and SMR evaluation we determined
activation energies (Q) and preexponent factors (D0) for the distinct
environment in the FePd samples. We obtained the highest activation energy
(1.82\pm0.38 eV)and lowest preexponential factor((5.76\pm0.35)*10-14 m2/s) for
the ordered L10 as oppose to the iron rich regions were the activation energy
(1.48\pm0.26 \pmV) found to be lowest and the preexponential factor the highest
((1.01\pm0.61)*10-13 m2/s).
