Aging effect in Magnetotransport Property of Oxygen adsorbed BaFe2As2

Presence of Oxygen (O2) has been found by Energy Dispersive X-ray Analysis (EDAX) on the surfaces of flux grown BaFe2As2 single crystals which were kept in air ambience for several months. Transport studies show that the O2 adsorbed crystals are more resistive and do not display any sharp slope change near 140 K which is the well known Spin Density Wave (SDW) transition temperature (TSDW) accompanying structural transition for as grown BaFe2As2. An anomalous slope change in resistivity is observed around 18 K at 0 and 5T. Magnetoresistance (MR) is noticed to increase as a function of applied field (H) quite differently than that for as grown crystals below TSDW which may be attributed to aging effec