Influence of oxygen stoichiometry on Co3+spin state transitions and magnetic properties in EuBaCo2O5+ cobaltites

The layered EuBaCo2O5+delta (delta = 0.47) (EBCO) cobaltite shows various magnetic phases at high temperature and magnetic glassy state at low temperature. Further, the various magnetic phases of the EBCO are coupled with the spin state transition of Co3+ octahedra. In the present study, we report the structural and magnetization properties of the EBCO by changing the oxygen stoichiometry. The various oxygen compositions were obtained after post annealing the as-prepared EBCO cobaltite under argon and oxygen atmospheres and the final stoichiometry was detected from the iodometric titrations. The delta = 0.13 and 0.67 samples show the tetragonal symmetry (space group, P4/mmm), whereas the delta = 0.41, 0.47 and 0.58 samples show the orthorhombic symmetry (space group, Pmmm). The magnetization measurements on the delta = 0.13 sample shows the paramagnetic to antiferromagnetic ordering at TN = 288 K and the electrical resistivity analysis shows the Co2+ and Co3+ charge ordering at TCO = 180 K. Further, the delta = 0.13 sample show the absence of the ferromagnetic phase and Co3+ spin state transitions. The delta = 0.58 and 0.67 samples show the coexistence of ferromagnetic and antiferromagnetic phases, however, the features of Co3+ intermediate spin (IS) to low spin (LS) state transition is suppressed, which is observed in delta = 0.47 sample at 151 K. Our results indicate a tuning of the crystal structure along with the magnetic properties and also the Co3+ spin state transitions by oxygen stoichiometry variation in EuBaCo2O5+delta cobaltites.