Curie temperature enhancement in the double perovskite Sr2-xLaxFeMoO6 system: An experimental study

In this work an experimental study on the synthesis and magnetic and structural properties of double perovskite compoundsSr(2-x)La(x)FeMoO(6) fabricated via a sol-gel process is presented. This method allowed to prepare doped systems with x values of 0, 0.25, 0.5, 0.75 and 1.0. The tetragonal crystalline structure was confirmed by X-ray diffraction experiments for all the compounds, which shows an increase of both the lattice parameters and the unit cell volume with La doping. According to X-ray photoelectron spectroscopy, it was found that in the above Fe-Mo compound, the Fe is mainly Fe3+ and the Mo is Mo5+ even though Fe shift to Fe(2+ )when x increases. Scanning electron microscopy observations have confirmed the granular and percolated morphology of the samples. Besides, the Curie temperature obtained by thermogravimetric analysis shows a substantial increase with La doping. As predicted by previous theoretical results, the increase of the Curie temperature in this system is consistent with the partial substitution of divalent Sr ions by trivalent La ions. Although the neutral total charge per formula is predicted to be preserved, the disorder induced in Fe-Mo sites decreases the magnetization, which is accompanied with an increase of the coercive field due the addition of La impurities that act as domain walls pinning sites. Finally, the experimental results presented in this work are helpful for the understanding of the underlying magnetic properties of doped double perovskites, which are of paramount importance for the development of spintronic devices with enhanced Curie temperature values.