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Crystals 2018, 8(11), 411;

Impurity-Induced Spin-State Crossover in La0.8Sr0.2Co1−xAlxO3

Department of Physics, Nagoya University, Nagoya 464-8602, Japan
Author to whom correspondence should be addressed.
Received: 26 September 2018 / Revised: 29 October 2018 / Accepted: 29 October 2018 / Published: 31 October 2018
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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We have prepared a set of polycrystalline samples of La 0.8 Sr 0.2 Co 1 x Al x O 3 ( 0 x 0.2 ), and have measured the magnetization as functions of temperature and magnetic field. We find that the average spin number per Co ion ( S Co ) evaluated from the room-temperature susceptibility is around 1.2–1.3 and independent of x. However, we further find that S Co evaluated from the saturation magnetization at 2 K is around 0.3–0.7, and decreases dramatically with x. This naturally indicates that a significant fraction of the Co 3 + ions experience a spin-state crossover from the intermediate- to low-spin state with decreasing temperature in the Al-substituted samples. This spin-state crossover also explains the resistivity and the thermopower consistently. In particular, we find that the thermopower is anomalously enhanced by the Al substitution, which can be consistently explained in terms of an extended Heikes formula. View Full-Text
Keywords: cobalt oxide; spin polaron; impurity effect; spin-state crossover cobalt oxide; spin polaron; impurity effect; spin-state crossover

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Terasaki, I.; Ikuta, M.; Yamamoto, T.D.; Taniguchi, H. Impurity-Induced Spin-State Crossover in La0.8Sr0.2Co1−xAlxO3. Crystals 2018, 8, 411.

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