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Strain Relaxation Effects on the Valence-Driven Spin-State/Metal-Insulator Transition in Epitaxial (Pr<sub>1-y</sub>Y<sub>y</sub>)<sub>1-x</sub>Ca<sub>x</sub>CoO<sub>3-δ</sub> Films

ORAL

Abstract

Pr-based cobaltites such as Pr1-xCaxCoO3-δ and (Pr1-yYy)1-xCaxCoO3-δ exhibit remarkable first-order coupled spin-state/metal-insulator/structural transitions driven by a unique Pr valence transition. While such phenomena are restricted to cryogenic temperatures in bulk, recent work of ours stabilized a valence transition to Tvt = 245 K in compressively strained (Pr1-yYy)1-xCaxCoO3-δ films. Here, we explore the effects of strain relaxation in such films. Careful analysis of temperature-dependent resistivity reveals splitting of the valence transition into two with increasing film thickness, one at the fully strained Tvt and one at the bulk Tvt. In-plane and out-of-plane lattice parameters from specular X-ray diffraction and asymmetric reciprocal space maps support this picture, evidencing partial strain relaxation with increasing thickness. Remarkably, in the ultrathin limit below ~10 unit cells, Tvt remains constant but the resistivity change across the transition is suppressed, destroying the high-temperature metallic state. We discuss possible origins of this low thickness behavior. Our results shed further light on the strain control of these unique spin-state/metal-insulator/structural/valence transitions.

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Publication: A paper is planned from this work.

Presenters

  • John E Dewey

    Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA, University of Minnesota

Authors

  • John E Dewey

    Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA, University of Minnesota

  • Vipul Chaturvedi

    University of Minnesota, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA

  • William M Postiglione

    University of Minnesota, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA

  • Andrew Jacobson

    University of Minnesota, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA

  • Caroline Korostynski

    Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA, University of Minnesota

  • Chris Leighton

    University of Minnesota, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, USA