Optical conductivity in La0.8Sr0.2Mn1−xRuxO3

The series La0.8Sr0.2Mn1−xRuxO3 ( 0 ≤ x ≤ 0.15 ) were prepared by an organic gel-assisted citrate process in order to perform infrared measurements. The Curie ( T C ) and the metal–insulator ( T IM ) transition temperatures decrease when the Ru content increases, and it is associated to a more and more insulating behaviour. In the optical conductivity at room temperature, the middle infrared region upshifts by transiting from the metallic to the insulating state according to increased carrier localisation. Ru breaks the long-range magnetic order and softens the double exchange interaction because the optical measurements show us that Ru favours the carrier localisation energy.