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arXiv · 1210.1289

Spin-state transition, magnetism and local crystal structure in Eu_{1-x}Ca_xCoO_{3-d}

A. N. Vasiliev·T. M. Vasilchikova·O. S. Volkova·A. A. Kamenev·A. R. Kaul·T. G. Kuzmova·D. M. Tsymbarenko·K. A. Lomachenko·A. V. Soldatov·S. V. Streltsov·J. -Y. Lin·C. N. Kao·J. M. Chen·M. Abdel-Hafiez·A. U. B. Wolter·R. Klingeler
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Abstract

The doping series Eu1-xCaxCoO3-d provides a rather peculiar way to study the spin-state transition in cobalt-based complex oxides since partial substitution of Eu3+ ions by Ca2+ ions does not increase the mean valence state of cobalt but is accompanied by appearance of oxygen vacancies in the ratio d \sim x/2. In the parent compound EuCoO3, the low spin (LS)-high spin (HS) transition takes place at temperatures so high that the chemical decomposition prevents its direct observation. The substitution of Eu3+ for Ca2+ in this system shifts the LS-HS transition to lower temperatures. The energy gap associated with this transition in octahedrally-coordinated Co3+ ions changes from 1940 K in EuCoO3 to 1540 K in Eu0.9Ca0.1CoO2.95 and 1050 K in Eu0.8Ca0.2CoO2.9. Besides, each O2- vacancy reduces the local coordination of two neighboring Co3+ ions from octahedral to pyramidal thereby locally creating magnetically active sites which couple into dimers. These dimers at low temperatures form another gapped magnetic system with very different energy scale, D~3 K, on the background of intrinsically non-magnetic lattice of octahedrally-coordinated low-spin Co3+ ions.

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A. N. Vasiliev, T. M. Vasilchikova, O. S. Volkova, A. A. Kamenev, A. R. Kaul, T. G. Kuzmova, D. M. Tsymbarenko, K. A. Lomachenko, A. V. Soldatov, S. V. Streltsov, J. -Y. Lin, C. N. Kao, J. M. Chen, M. Abdel-Hafiez, A. U. B. Wolter, R. Klingeler. 2012-10-04. Spin-state transition, magnetism and local crystal structure in Eu_{1-x}Ca_xCoO_{3-d}. https://doi.org/10.7566/jpsj.82.044714

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