Magnetic phase evolution in Fe substituted GdBaCo₂O_5.5

Abstract

Magnetization and magneto-resistance experiments have been carried out on well characterized samples of the GdBaCo_2-xFe_xO_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 GdBaCo₂O_5.5, is suggested.