Giant isotope effect and spin state transition induced by oxygen isotope exchange in ($P{r}_{1-x}S{m}_x{)}_{0.7}C{a}_{0.3}Co{O}_3$

Abstract

We systematically investigate effect of oxygen isotope in $(P{r}_{1-x}S{m}_x{)}_{0.7}C{a}_{0.3}Co{O}_3$ 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 ${\alpha }_S=-4.7$ 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.

4 pages, 5 figures

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