Mössbauer study of the (Ru1-xFex)Sr2GdCu2O8-δ system and two of its possible impurities: SrRuO3 and Gd2CuO4

Abstract

Mössbauer spectra of a series of samples of the weak ferromagnetic (Ru1-xFex)Sr2GdCu2O8-δ system reveal the existence of three dissimilar sites where the Fe atoms can go into the structure. The Mössbauer parameters of the three observed quadrupole doublets, together with the relative population on each site, allow the following site assignment for the iron atoms: Fe3+ in four-fold planar coordination at Ru sites; Fe3+ in five-fold pyramidal coordination also at Ru sites and Fe2+ or Fe3+ in five-fold coordination at Cu sites. This assignment implies the formation of oxygen-vacancies at the charge reservoir (the RuO2 planes) that affect the structure and the superconducting and magnetic properties of the undoped system. Moreover, a close correlation between the oxygen content, calculated through the Mössbauer data, and the measured cell volume is established. We also report the Mössbauer spectra of two compounds (SrRu0.95Fe0.05O3 and Gd2Cu0.95Fe0.05O4) that could be formed as impurities during the synthesis of our samples.