Colossal magnetoresistance in CaxSr2-xFeReO6 double perovskites due to field-induced phase coexistence
Résumé
We have investigated the properties of the low-temperature magnetostructural transition in polycrystalline CaxSr2−xFeReO6 compounds. We have shown in a previous report that this kind of transition was present for x⩾1. We have observed that the temperature dependence of the resistivity, the lattice parameters, and the magnetocrystalline anisotropy of the x=1.5 compound mimics those of the x=2 compound. Therefore, the coexistence of two monoclinic phases with different conductivities and crystallographic parameters, which is well reported for x=2, is suggested to occur also for x=1.5. Since the external applied field favors the high-temperature phase, we have performed magnetostriction and magnetoresistance experiments up to 25 and 45T, respectively, in order to track macroscopically the phase coexistence. In the x=1.5 compound, we find magnetoresistance above 2000%, which is an unexpected phenomenon in the field of double perovskites. Furthermore, the magnetostriction isotherms under high fields behave in a nonmonotonous way due to the different cell volumes of the coexisting phases. These results indicate that the field-induced phase coexistence is a general property in CaxSr2−xFeReO6 compounds showing large monoclinic distortion.
Origine : Fichiers éditeurs autorisés sur une archive ouverte
