EFFECT OF Eu DOPING AND PARTIAL OXYGEN ISOTOPE SUBSTITUTION ON MAGNETIC PHASE TRANSITIONS IN ( Pr_1-y Eu_y)_0.7 Ca_0.3 CoO₃ COBALTITES
Babushkina N.A., Taldenkov A.N., Streltsov S.V., Kalinov A.V., Kuzmova T.G., Kamenev A.A., Kaul A.R., Khomskii D.I., Kugel K.I.

Received: May 22, 2013

DOI: 10.7868/S0044451014020114

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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 CoO₃ 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, 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 the change of the Eu and ¹⁸ O content. It is demonstrated that the effect of increasing the 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 reveals the physical mechanisms underlying this similarity.