Influence of La and Mn vacancies on the electronic and magnetic properties of LaMnO$_{3}$ thin films grown by pulsed laser deposition

摘要

With pulsed laser deposition we have grown c-axis oriented thin films of thenominal composition LaMnO$_{3}$ (LMO) on LSAT(001) substrates. We find that,depending on the oxygen background pressure during growth, the LMO filmscontain sizeable amounts of La and/or Mn vacancies that strongly influencetheir electronic and magnetic properties. Specifically, we show that the Mn/Laratio can be systematically varied from 0.92 at 0.11 mbar to 1.09 at 0.30 mbarof oxygen. These cationic vacancies lead to markedly different disorder effectsthat become most pronounced once the samples are fully oxygenated and thusstrongly hole doped. All as-grown and thus slightly oxygen deficient LMO filmsare ferromagnetic insulators with saturation moments in excess of 2.5 \mu$_{B}$ per Mn ion, their transport and optical properties that can beunderstood in terms of trapped ferromagnetic polarons. Upon oxygen annealing,the most La-deficient films develop a metallic response with an even largerferromagnetic saturation moment of 3.8 \mu $_{B}$ per Mn ion. In contrast, inthe oxygenated Mn-deficient films the ferromagnetic order is almost completelysuppressed to less than 0.5 \mu $_{B}$ per Mn ion and the transport remainsinsulator-like. We compare our results with the ones that were previouslyobtained on bulk samples and present an interpretation in terms of the muchstronger disorder potential of the Mn vacancies as compared to the Lavacancies. We also discuss the implications for the growth of LMO thin filmswith well-defined physical properties that, for example, are a prerequisite forthe study of interface effects in multilayers.