Magnetic phase evolution in Fe substituted GdBaCo2O5.5

Magnetization and magneto-resistance experiments have been carried out on well characterized samples of the GdBaCo(2-x)FexO(5.5) series. Zero field cooled magnetization measurements in the low concentration Fe samples suggest, that the low temperature anti-ferromagnetic phase transforms sequentially to several ferromagnetic phases, before transforming to a paramagnetic state with increase in temperature. The anti-ferromagnetic to the first ferromagnetic phase transition is associated with a large negative magneto-resistance for Fe fractions up to x=0.075. Isothermal magnetization measurements in the ferromagnetic like region of the samples, suggests the presence of mixtures of two ferromagnetic phases. Similar measurements performed at low temperatures where anti-ferromagnetic-like phase is stabilised suggest the presence of a mixture of anti-ferromagnetic and ferromagnetic phases. Magnetization and magneto-resistance are seen to collapse for Fe fractions, x > 0.1. Based on these studies a plausible scenario of the evolution of magnetism with Fe substitution in GdBaCo2O5.5, is suggested. (C) 2009 Elsevier B.V. All rights reserved.