Abstract
We present the study of magnetization, thermal expansion, specific heat, resistivity, and ac susceptibility of cobaltites. The measurements were performed on ceramic samples with and . Based on these results, we construct the phase diagram, including magnetic and spin-state transitions. The transition from the low-to-intermediate spin state is observed for the samples with , whereas for a lower Eu-doping level, there are no spin-state transitions, but a crossover between the ferromagnetic and paramagnetic states occurs. The effect of oxygen isotope substitution along with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope substitution ( by ) is found to shift both the magnetic and spin-state phase boundaries to lower Eu concentrations. The isotope effect on the spin-state transition temperature is rather strong but it is much weaker for the transition to a ferromagnetic state . The ferromagnetic ordering in the low-Eu-doped samples is shown to be promoted by the ions, which favor the formation of the intermediate-spin state of neighboring ions.
4 More- Received 22 July 2009
DOI:https://doi.org/10.1103/PhysRevB.81.134427
©2010 American Physical Society