Magnetic phase evolution in Fe substituted GdBaCo2O5.5

Abstract Magnetization and magneto-resistance experiments have been carried out on well characterized samples of the GdBaCo 2− x Fe x O 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 upto 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 GdBaCo 2 O 5.5 , is suggested.