Electron Injection and ``Oxygen Effect'' in BaFe$_{2}$As$_{2}$: M\"{o}ssbauer Studies

It is widely believed that a few percent substitution of Co (with d7) or Ni (with d8) for Fe (with d6) in BaFe$_{2}$As$_{2}$ results in donation~of electrons, killing of magnetism, and thereby induction of superconductivity. We are exploring the possibility of injecting electrons by physico-chemical techniques instead of substitutions.~ We have also discovered that traces of chemisorbed oxygen can change drastically the magnetic behavior in polycrystalline BaFe$_{2}$As$_{2}$ at low temperatures. BaFe$_{2}$As$_{2}$ exhibits considerable hysteresis~behavior as well that of thermal history.