Effect of Eu doping and partial oxygen isotope substitution on magnetic phase transitions in (Pr1 - Y Eu y )0.7Ca 0.3CoO3 cobaltites

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 (Pr1 - y Eu y )0.7Ca0.3CoO3 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 18O, namely, with 90, 67, 43, 17, and 0% of 18O. Based on the measurements of the ac magnetic susceptibility χ(T) and electrical resistivity ρ(T), we analyze the evolution of the sample properties with a change of the Eu and 18O content. It is demonstrated that the effect of increasing the 18O 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 reveals the physical mechanisms underlying this similarity. © 2014 Pleiades Publishing, Inc.