Molecular Foundry Seminar

"Spin State Mapping with Atomic Resolution"

Dr. Jaume Gazquez, Oak Ridge National Laboratory (Currently at ICMAB-CSIC, Spain)
Tuesday, May 3rd at 1:00 pm, Bldg. 67 - 3111

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Abstract:

The mixed valences of transition and rare-earth metals can stabilize a variety of compounds with O deficiency. At the same time, these oxygen vacancies play a key role in determining the functionality of many oxide materials. The analysis of O vacancies is currently accessible using simultaneously aberration-corrected STEM annular dark-field (ADF) imaging and electron energy-loss spectroscopy (EELS).

Certain complex cobalt oxides with perovskite structure are known to exhibit ordered Co spin states. The O K edge in electron energy loss spectroscopy (EELS) is sensitive to the spin state of Co atoms [1], and is used here to image such spin state superlattice in La0.5Sr0.5CoO3-δ (LSCO) thin films in real space with atomic resolution [2]. First principles calculations predict that a spin state ordering made of alternating planes with Co in high and low spin states can be stabilized in strained LSCO films through the ordering of oxygen vacancies. EELS images confirm that Co is significantly reduced and those Co atoms in the oxygen deficient CoO plane are in the high spin state, while the Co atoms in the fully oxygenated plane are in the low spin state.

[1]        R. F. Klie et al., Phys. Rev. Lett. 99, 047203 (2007).
[2]        J. Gazquez et al., Nano Lett. 11, 973-976 (2011).