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Abstract:
The effect of diamagnetic dilution of the Fe sublattice on the
structural and magnetic properties of the double perovskite
Sr2Fe1-xGaxReO6 (0 < x < 0.7) has been explored by means of x-ray
structural analysis, magnetometry, Mossbauer spectroscopy, and band
structure calculations. The end member of the solid solution series,
Sr2GaReO6, was predicted to be a half-metallic ferromagnet based on ab
initio band structure calculations using the WIEN2k software package.
Because the Re-containing double perovskites, like the parent compound
Sr2FeReO6, rarely exhibit antisite disorder, the appearance of
increasing amounts of antisite disorder in Sr2Fe1-xGaxReO6 (0 < x < 0.7)
is unexpected. Although the amount of antisite disorder increases with
increasing Ga content, it also depends on the sample preparation
history. For 0 < x < 0.4 only a tetragonal, magnetically ordered phase
was detected by x-ray structural analysis as well as Mossbauer analysis.
A phase separation into a tetragonal and a cubic phase for x >= 0.4 is
detected by x-ray structural analysis accompanied by the observation of
a magnetically ordered and a paramagnetic phase in the corresponding
Mossbauer spectra. Below 20% Ga content, Ga statistically dilutes the
-Fe-O-Re-O-Fe- double-exchange pathways. Phase separation begins at 20%
Ga substitution; between 20% and 40% of Ga content, the paramagnetic
Ga-based phase does not contain any Fe. The Fe-containing, paramagnetic
cubic phases which can be detected by Mossbauer spectroscopy first
appear for x=0.4.
