Effect of the internal pressure and the anti-site disorder on the structure and magnetic properties of ALaFeTiO ₆ (A=Ca, Sr, Ba) double perovskite oxides

Successful preparation of double perovskite oxides of chemical formula ALaFeTiO ₆ (A=Ba, Sr and Ca) has been achieved by following the precursor method. The samples were studied by means of X-ray diffraction and Mössbauer spectroscopy. The Rietveld analysis of the X-ray diffraction data showed that all the samples have anti-site disorder. The presence of anti-site disorder has altered the electronic environment around the Fe ion sites which creates electric field gradient between two different sites. Observation of quadruple splitting in the ideal cubic perovskite BaLaFeTiO ₆ (its tolerance factor equals 1) is the evidence of this anti-site generated electric field gradient. The valence state of the Fe atom determined from the measurements of the Mössbauer effect of ⁵⁷Fe at room temperature and 80 K showed that the iron ion has the Fe ³⁺ high spin state as extracted from the values of the isomer shift for all the samples. It is evidenced that the anti-site disorder has no appreciable effect on the spin state of the Fe ion, but alters the charge densities at the Fe sites and influences the hyperfine parameters of the present samples. Weak ferromagnetism is observed in CaLaFeTiO ₆ and SrLaFeTiO ₆ and is related to both the internal pressure and the anti-site effect which facilitate the occurrence of the Fe ³⁺↑-O-Fe ³⁺↓ antiferromagnetic interaction with canted spin.