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Abstract:
Strong correlations between the electronic, structural and magnetic
properties have been found during the study of doped double perovskites
Sr2Fe1-xMxReO6 (0 <= x <= 1, M = Zn, Cr). The interplay between the van
Hove singularity and the Fermi level plays a crucial role for the
magnetic properties. Cr doping of the parent compound Sr2FeReO6 leads to
a non-monotonic behaviour of the saturation magnetization and an
enhancement for doping levels up to 10%. The Curie temperatures
monotonically increase from 401 to 616 K. In contrast, Zn doping leads
to a continuous decrease in the saturation magnetization and the Curie
temperatures. Superimposed on the electronic effects is the structural
influence which can be explained by size effects modelled by the
tolerance factor t. For Cr doping levels higher than 40% we observed a
tetragonal-cubic transformation. For Zn doped samples the tetragonal
distortion linearly increases with the increasing Zn content. The
valence state of iron strongly influencing the structure was determined
by Mossbauer spectroscopy to be +2.7.
