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Insulator-to-Metal Transition of Cr2O3 Thin Films via Isovalent Ru3+ Substitution
journal contribution
posted on 2020-06-10, 19:05 authored by Kohei Fujiwara, Miho Kitamura, Daisuke Shiga, Yasuhiro Niwa, Koji Horiba, Tsutomu Nojima, Hiromichi Ohta, Hiroshi Kumigashira, Atsushi TsukazakiIn transition-metal
oxides, the vast combinations of crystal structures
and metal ions provide a fertile ground for tailoring their electronic
properties. Using a thin-film growth technique creates an additional
interface-related degree of freedom in the artificial heterostructures.
However, in corundum-type and crystallographically related ternary
compounds, the scarcity of oxides applicable to a lattice-matched
electrode layer often impedes the electrical characterization of these
heterostructures. Here, we report the synthesis of a thin film of
a new corundum-type oxide that exhibits metallic conduction. By substituting
Ru into the antiferromagnetic insulator Cr2O3 via pulsed laser deposition, we fabricated thin films of (Cr1–xRux)2O3 not known in bulk. The structural, electrical,
and magnetic characterizations showed that the antiferromagnetic insulator
became a paramagnetic metal at Ru contents x greater
than approximately 0.40 while preserving the host corundum structure.
Spectroscopic analyses revealed the formation of Ru 4d-derived bands
at the Fermi level and the presence of Ru3+, which is a
valence state of Ru rarely observed in oxides. The stabilization of
the unusual Ru3+ state is attributed to the charge neutrality
constraint in the robust Cr2O3-based framework
as well as the kinetics-driven vacuum deposition process.
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Keywords
antiferromagnetic insulator Cr 2 O 3transition-metal oxidesinterface-related degreeSpectroscopic analysesRu contents xmetal ionsthin-film growth techniquecharge neutrality constraintternary compoundskinetics-driven vacuum deposition processFermi levelcorundum-type oxideCr 2 O 3valence stateInsulator-to-Metal Transitionlaser deposition2 O 3Ru 4 d-derived bandshost corundum structurelattice-matched electrode layercrystal structuresantiferromagnetic insulator