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Giant isotope effect and spin state transition induced by oxygen isotope exchange in ($Pr_{1-x}Sm_x)_{0.7}Ca_{0.3}CoO_3$

G. Y. Wang·X. H. Chen·T. Wu·G. Wu·X. G. Luo·C. H. Wang
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Abstract

We systematically investigate effect of oxygen isotope in $(Pr_{1-x}Sm_x)_{0.7}Ca_{0.3}CoO_3$ which shows a crossover with x from ferromagnetic metal to the insulator with spin-state transition. A striking feature is that effect of oxygen isotope on the ferromagnetic transition is negligible in the metallic phase, while replacing $^{16}O$ with $^{18}O$ leads to a giant up-shift of the spin-state transition temperature ($T_s$) in the insulating phase, especially $T_s$ shifts from 36 to 54 K with isotope component $α_S=-4.7$ for the sample with x=0.175. A metal-insulator transition is induced by oxygen isotope exchange in the sample x=0.172 being close to the insulating phase. The contrasting behaviors observed in the two phases can be well explained by occurrence of static Jahn-Teller distortions in the insulating phase, while absence of them in the metallic phase.

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G. Y. Wang, X. H. Chen, T. Wu, G. Wu, X. G. Luo, C. H. Wang. 2006-04-30. Giant isotope effect and spin state transition induced by oxygen isotope exchange in ($Pr_{1-x}Sm_x)_{0.7}Ca_{0.3}CoO_3$. https://doi.org/10.1103/physrevb.74.165113

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