Effects of the lanthanide addition to the Sr_2CrReO_6 double perovskite

摘要

We have studied the effects of Sr replacement by different lanthanides in Sr_2CrReO_6. Our attempts at electron doping of Sr_2CrReO_6 led to multiphasic systems. Single phases are only obtained with the stoichio-metric formula Sr_(2-x)Ln_x:Cr_(1+x/2)O_6. We have studied the properties of these compounds with x≤0.5 and Ln=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 Sr_(2-x)Nd_xCr_(1+x/2)Re_(1-x/2)O_6 and Sr_(2-x)Sm_xCr_(1+x/2)Re_(1-x/2)O_6 (x≤0.5) by means of x-ray absorption spectroscopy. The spectra at the Cr K edge agree with the presence of 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 Re L_(1,2,3) edges reveal the presence of Re~(5+) in all compounds. This implies that replacing Sr by Ln does not affect the electronic state of both Cr~(3+) and Re~(5+).