Structural, spin state, and magnetic transitions in GdBaCo2O5-delta (deltaapproximate to 0.5)

Structural, spin state, magnetic and field-induced transitions have been st udied in GdBaCo2O5.5 over a wide range of temperatures. We have found that, concomitant with a metal-insulator transition at 370 K, remarkable structu ral changes take place. These changes evidence the onset of orbital order a t this temperature. Magnetization measurements, and the observation of a fi eld-induced transition, below 250 K, by applying high magnetic fields, conf irm that, below this temperature, an antiferromagnetic arrangement of the m agnetic moments is present. (C) 2001 Elsevier Science B.V. All rights reser ved.