Effect of Anionic Stoichiometry and Composition Variations on the Structural and Electrical Properties of Mixed Valent Manganite Thin Films

Thin films of rare earth manganites of the generic composition (RE)_1-x(AE)_xMnO₃ are well known for electronic phenomena such as insulator-metal transitions, charge ordering and colossal magnetoresistance. These phenomena are sensitive to the compositional variations at the RE and AE sites, as well as variations in oxygen stoichiometry, both of which control the Mn valence state distribution. In addition, the structural changes accompanying these compositional changes influence these properties through effects such as Jahn-Teller distortions and local strain fields promoting electronic phase separation. We will present the results of our experiments designed to controllably create oxygen vacancies in epitaxial thin films and partially substitute oxygen by fluorine through a post-deposition heat treatment . We observe structural changes as well as changes in electrical transport properties upon subjecting the films to the fluorination process. These changes will be discussed in the light of possible charge doping and structural changes introduced as a result of the differences in valence state and ionic sizes of oxygen and fluorine.