Abstract
Using soft x-ray absorption spectroscopy we were able to determine unambiguously the charge and spin states of the transition metal ions in stoichiometric and . The trivalent and low-spin nature of both the Cu and Co ions in makes this correlated system to be effectively a nonmagnetic band semiconductor. The substitution of Y by Ca produces formally tetravalent Co ions but the doped holes are primarily on the oxygen ligands. Concerning the spin degrees of freedom, the trivalent Co ions in remain low spin upon the Y-Ca substitution, very much unlike the system. The tetravalent Co ions in are interestingly also in the low-spin state, which then explains the good electrical conductivity of since charge exchange between neighboring and ions will not be hampered by the spin-blockade mechanism that otherwise would be in effect if the and spin quantum numbers were to differ by more than one-half. We infer that the stability of the Co low-spin state is related to the very short Co-O bond lengths.
1 More- Received 28 December 2020
- Accepted 11 March 2021
DOI:https://doi.org/10.1103/PhysRevB.103.115149
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