Europium valencies in substitued EuCu2Si2 systems

Moessbauer studies of 151Eu in EuCu2-xPtxSi2, EuCu2Si2-xGex and EuxGd1-xMn2Si2 (x≤0.25) at temperatures between 90 K and 425 K have been performed. All spectra are composed of at least two subspectra, corresponding to stable Eu2+ and intermediate valent Eu. The isomer shift of the stable divalent Eu (ordered magnetically up to 400 K in Eu0.25Gd0.75Mn2Si2) is S2=-7.5 mm/sec in comparison to S2=-10.5 mm/s for stable Eu2+ in EuMn20Ge2. This shows that the Eu2+ is under heavy internal pressure in these systems. From the temperature dependence of the hyperfine interaction parameters and line intensities conclusions are derived concerning interconfigurational excitation energies, their inhomogeneous width and recoil free fraction behaviour. (orig.)