Room-Temperature Valence Transition in a Strain-Tuned Perovskite Oxide

Abstract

Cobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing cobalt oxides, where a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by a remarkable praseodymium valence transition. Such valence transitions, particularly when triggering spin-state and metal-insulator transitions, offer highly appealing functionality, but have thus far been confined to cryogenic temperatures in bulk materials (e.g., 90 K in Pr1-xCaxCoO3). Here, we show that in thin films of the complex perovskite (Pr1-yYy)1-xCaxCoO3-δ, heteroepitaxial strain tuning enables stabilization of valence-driven spin-state/structural/metal-insulator transitions to at least 291 K, i.e., around room temperature. The technological implications of this result are accompanied by fundamental prospects, as complete strain control of the electronic ground state is demonstrated, from ferromagnetic metal under tension to nonmagnetic insulator under compression, thereby exposing a potential novel quantum critical point.

35 pages, 7 figures

References in corpus (7)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• The spin state transition in LaCoO${}_3$; revising a revision
• Physics of ultrathin films and heterostructures of rare earth nickelates
• Strain-Induced Spin States in Atomically Ordered Cobaltites
• Suppression of the ferromagnetic state in LaCoO3 films by rhombohedral distortion
• Exploiting symmetry-mismatch to control magnetism in a ferroelastic heterostructure

Cited by in corpus (1)

• Chemical Design of Electronic and Magnetic Energy Scales in Tetravalent Praseodymium