Doping Ru/Cr on B-site of La(BaCa)MnO thin films: driving insulator-to-metal transition temperature far apart from Curie temperature

Abstract

Magnetic and transport properties of Ru/Cr doped La(Ba,Ca)MnO thin films fabricated by the pulsed laser deposition technique on (1 0 0) LaAlO 3 substrates have been investigated. Ru-doping reduces both Curie temperature ( T C) and insulator-to-metal temperature ( T IM) in LaBaCaMnO thin films: under zero field, La 0.7Ba 0.1Ca 0.2Mn 0.9Ru 0.1O 3 thin films which have T C about 190 K show an insulator-to-metal transition at 75 K. It is likely that Ru-doping creates some antiferromagnetic insulating matrix which separates a basically ferromagnetic background into isolated ferromagnetic domains. In the case of partial substitution of Cr for Mn in La 0.9Ba 0.1MnO 3 thin films, while T C remains almost the same as non-doped films, the magnitude of the magnetization is increased very much due to doping. However, this enhancement does not go along with the enhancement of metallicity: upon doping, T IM shifts to lower temperatures, and the resistivity becomes several orders higher as well. The nature of T IM being far apart from T C in Cr-doped samples are thought to be different from that of Ru-doped ones: it is supposed that the Cr substitution created inhomogeneities resulting in various bonds such as Cr 3+OCr 3+, Mn 3+OCr 3+ and MnOMn. The observation of T IM far below T C in B-site doping manganite thin films is very anomalous and cannot be explained by double-exchange theory.