Electron doping versus antisite defects: Structural and magnetic properties of Sr2−xLaxCrMoO6 and Sr2−xLaxCr1+x/2Mo1−x/2O6 perovskites

This study reports the synthesis, structure and magnetic properties of Sr2−xLaxCrMoO6 and Sr2−xLaxCr1+x/2Mo1−x/2O6 samples. Although both series exhibit similar crystal structures, Sr2−xLaxCrMoO6 samples present an effective electron doping revealed by a significant expansion of the unit cell with increasing x. In Sr2−xLaxCr1+x/2Mo1−x/2O6 samples instead, the Cr-excess leads to a non electron doped system. Both series show a large amount of antisite defects whose number increases as La-content increases. Neutron diffraction patterns reveal the existence of long-range magnetic ordering for all samples but the magnetic peaks are very broad for Sr2CrMoO6 indicating a short coherence length of the magnetic ordering. This coherence length is increased upon replacing Sr by La. In both systems there is a clear increase of the magnetic transition temperature with increasing the La-content. The samples show ferromagnetic contributions at low temperature as deduced from the magnetic hysteresis loops typical of hard ferromagnetic materials. However, magnetic saturation is not achieved even at 5 T and the magnetic moment at this field is small. The ac magnetic susceptibility reveals the existence of several anomalies suggesting that these compounds are magnetically inhomogeneous. This is probably due to the presence of the large amount of structural defects not homogenously distributed.

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