Effect of Eu doping and partial oxygen isotope substitution on magnetic phase transitions in (Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites

TL;DR

This study investigates how Eu doping and oxygen isotope substitution influence magnetic phase transitions and spin states in cobaltite materials, revealing similar effects from both modifications and elucidating the underlying mechanisms through experimental and theoretical analysis.

Contribution

It provides new insights into the combined effects of Eu doping and oxygen isotope substitution on magnetic and transport properties of cobaltites, supported by band structure calculations.

Findings

Increasing $^{18}$O content mimics the effect of Eu doping on magnetic properties.

The similarity is explained by changes in the energy gap influenced by electron-phonon interactions.

Experimental results show shifts in magnetic susceptibility and resistivity with isotope and doping variations.

Abstract

We study experimentally and theoretically the effect of Eu doping and partial oxygen isotope substitution on the transport and magnetic characteristics and spin-state transitions in (Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites. The Eu doping level $y$ is chosen in the range of the phase diagram near the crossover between the ferromagnetic and spin-state transitions ($0.10 < y < 0.20$). We prepared a series of samples with different degrees of enrichment by the heavy oxygen isotope $^{18}$O, namely, containing 90%, 67%, 43%, 17%, and 0% of $^{18}$O. Based on the measurements of ac magnetic susceptibility $\chi(T)$ and electrical resistivity $\rho(T)$, we analyze the evolution of the sample properties with the change of Eu and $^{18}$O content. It is demonstrated that the effect of increasing $^{18}$O content on the system is similar to that of increasing the Eu content. The band structure calculations of the energy gap between $t_{2g}$ and $e_g$ bands including the renormalization of this gap due to the electron-phonon interaction reveal the physical mechanisms underlying such similarity.