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

TL;DR

This study reveals that oxygen isotope exchange causes a giant shift in spin-state transition temperature in ($Pr_{1-x}Sm_x)_{0.7}Ca_{0.3}CoO_3$, especially in the insulating phase, highlighting isotope effects on magnetic and electronic phase transitions.

Contribution

It demonstrates the significant impact of oxygen isotope substitution on spin-state transitions and metal-insulator transitions in a cobaltite system, with phase-dependent effects.

Findings

Giant up-shift of $T_s$ with isotope exchange in insulating phase

Negligible isotope effect on ferromagnetic transition in metallic phase

Oxygen isotope exchange induces a metal-insulator transition near the phase boundary

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 $\alpha_S=-4.7$ 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.