Mossbauer effect in hydrogenated Fe-Ni alloys

Distribution of hydrogen and its interaction with iron in hydrogenated ferromagnetic Fe-45 at.% Ni alloy were studied by means of 57 Fe Mossbauer spectroscopy. As a result of hydrogenation two phases (FCC gamma ' and FCC beta ) appeared, and the Mossbauer spectrum was separated into two components. One corresponding to gamma ' exhibits very small changes in the Mossbauer parameters compared with the original gamma phase, while the other corresponding to beta has a large positive isomer shift change, line broadening, and a remarkable internal field reduction. In the gamma ' phase presumably hydrogen atoms prefer the interstitial sites close to nickel atoms producing inhomogeneous distribution, large lattice distortions and no direct interaction with iron atoms. In the hydride-like beta phase, hydrogen atoms will have an ordered structure and may interact strongly with iron atoms, by which the 3d state of iron will be considerably changed and the magnetic moment of iron reduced. The lattice expansion seems to contribute only one-third of the isomer shift change.