Effects of the lanthanide addition to theSr2CrReO6double perovskite

Abstract

We have studied the effects of Sr replacement by different lanthanides in ${\mathrm{Sr}}_{2}\mathrm{Cr}\mathrm{Re}{\mathrm{O}}_{6}$. Our attempts at electron doping of ${\mathrm{Sr}}_{2}\mathrm{Cr}\mathrm{Re}{\mathrm{O}}_{6}$ led to multiphasic systems. Single phases are only obtained with the stoichiometric formula ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{Ln}}_{x}{\mathrm{Cr}}_{1+x∕2}{\mathrm{Re}}_{1\ensuremath{-}x∕2}{\mathrm{O}}_{6}$. We have studied the properties of these compounds with $x\ensuremath{\leqslant}0.5$ and $\mathrm{Ln}=\mathrm{La}$, Nd, or Sm. All of these samples crystallize in a face-centered cubic cell, which shrinks as Ln-size decreases. The distribution of Re and Cr atoms has been solved using x-ray diffraction. The samples show spontaneous magnetization at room temperature with large coercive fields. The Ln addition slightly affects the Curie temperature although the saturated magnetic moment decreases, owing to the increase of antisite defects. We have also studied ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{Cr}}_{1+x∕2}{\mathrm{Re}}_{1\ensuremath{-}x∕2}{\mathrm{O}}_{6}$ and ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{Sm}}_{x}{\mathrm{Cr}}_{1+x∕2}{\mathrm{Re}}_{1\ensuremath{-}x∕2}{\mathrm{O}}_{6}$ $(x\ensuremath{\leqslant}0.5)$ by means of x-ray absorption spectroscopy. The spectra at the $\mathrm{Cr}\phantom{\rule{0.2em}{0ex}}K$ edge agree with the presence of ${\mathrm{Cr}}^{3+}$ for all compounds although changes with increasing the rare-earth content are visible at the preedge features. These changes suggest a change in the Cr-O covalency of the samples with increasing Ln content. Measurements at the $\mathrm{Re}\phantom{\rule{0.2em}{0ex}}{L}_{1,2,3}$ edges reveal the presence of ${\mathrm{Re}}^{5+}$ in all compounds. This implies that replacing Sr by Ln does not affect the electronic state of both ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Re}}^{5+}$.