Magnetic and chemical superstructures in Gd2PdSi3 studied using synchrotron radiation

$R_{2}$PdSi$_{3}$ compounds have stimulate a recent interest due to the coexistence of long-range antiferromagnetic order and spin-glass like behavior. We present x{\-}ray resonant magnetic scattering studies on a Gd$_{2}$PdSi$_{3}$ single crystal at temperatures between 8~K and 30~K performed on the MUCAT beamline, APS, Argonne. Charge satellite reflections were observed with the propagation vectors (1/2~0~1/8) and (1/2~0~1/3). The corresponding chemical superstructure can be described by an ordered distribution of the Pd and Si ions on the B site in the hexagonal AlB$_{2}$ derived structure. Below $T_{N}$~=~23~K antiferromagnetic satellite reflections appear. The propagation vector is incommensurate with temperature dependent values between (0.14~0~0) and (0.13~0~0). This emphasizes the dominance of the RKKY interaction in Gd$_{2}$PdSi$_{3}$ in comparison to the strong influence of crystal electric field effects in the other $R_{2}$PdSi$_{3}$ compounds.