High magnetic field study of HoBaCo2O5.5 and GdBaCo2O5.5 layered cobaltites:: the effect of rare-earth size

By means of high-pulsed magnetic field up to mu(o)H = 32 T we have studied HoBaCo2O5+delta (delta = 0.52(1)). The high-field M(H) integrated curves evidence a magnetic field-induced phase transition visible from about T = 75 to 275 K. The obtained results are compared with the field-induced transition found for GdBaCo2O5+delta (with delta = 0.54(2)). The jump of the magnetization at the field-induced transition is independent of the rare earth at this level of oxygen content. In contrast, we have observed larger values of the critical field, and that the transition persists up to higher temperature, when reducing the rare-earth size. This indicates that the low-temperature antiferromagnetic phase becomes more stable when the size of the rare earth is reduced. (C) 2004 Elsevier B.V. All rights reserved.