Valence transition and low field magnetoresistance in (Sr2 xBax)FeMoO6

The crystal structure, electronic transport and magnetic properties of double perovskite (Sr2−xBax)FeMoO6 () are investigated. These compounds exhibit a metal–insulator transition as a function of doping x. The valence transition from Fe3+–Mo5+ to Fe2+–Mo6+ when x exceeds the critical concentration x = 1.6 can lead to a localization of the itinerant electrons and plays a key role in the metal–insulator transition. The bond distance data and composition dependence of the Curie temperature and magnetoresistance suggest this valence transition. The Curie temperature TC shows an enhancement on the Ba-poor side and decreases monotonically with x on the Ba-rich side, which can be understood in terms of two competing effects: anti-site defects and chemical pressure. The low field magnetoresistance shows a close correlation with the Curie temperature of the compounds.