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Oxygen Isotope Effect on the Spin State Transition in (Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$

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

Oxygen isotope substitution is performed in the perovskite cobalt oxide (Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$ which shows a sharp spin state transition from the intermediate spin (IS) state to the low spin (LS) state at a certain temperature. The transition temperature of the spin state up-shifts with the substitution of $^{16}O$ by $^{18}$O from the resistivity and magnetic susceptibility measurements. The up-shift value is 6.8 K and an oxygen isotope exponent ($α_S$) is about -0.8. The large oxygen isotope effect indicates strong electron-phonon coupling in this material. The substitution of $^{16}$O by $^{18}$O leads to a decrease in the frequency of phonon and an increase in the effective mass of electron ($m$$^\ast$), so that the bandwidth W is decreased and the energy difference between the different spin states is increased. This is the reason why the $T_s$ is shifted to high temperature with oxygen isotopic exchange.

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G. Y. Wang, T. Wu, X. G. Luo, W. Wang, X. H. Chen. 2005-10-19. Oxygen Isotope Effect on the Spin State Transition in (Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$. https://doi.org/10.1103/physrevb.73.052404

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