Experimental proof of the distinct electronic structure of a new meteoritic Fe-Ni alloy phase

We provide an experimental proof that the so-called 'paramagnetic phase' se en in Fe-Ni-bearing meteorites has a very different electronic structure fr om that of all other known Fe-Ni minerals, in support of the recent proposa l that it is a low moment phase and a new meteoritic mineral. Fe-57 Mossbau er isomer shift measurements, corrected for second-order Doppler shifts, gi ve local electronic densities at the probe nuclei corresponding to a surplu s local density of 0.42 electrons per Bohr radius cubed compared to the den sities of all other Fe-Ni minerals and all known high-moment synthetic Fe-N i alloys. This implies that the paramagnetic phase cannot simply be either Fe-rich high-moment face centered cubic phase (taenite) or atomically order ed Fe3Ni, as previously proposed, and it represents an unprecedented situat ion where two minerals (the new low moment phase, antitaenite, and taenite) have the same crystal structure and can have the same composition but diff er only in electronic structure and associated properties. We also report t he bulk production by mechanical alloying of synthetic low-moment Fe-Ni mat erial. These are the first observations of low moment Fe-Ni phases, giving insight into the conditions for metastability and the mechanisms of formati on of these unusual alloys. (C) 1999 Elsevier Science B.V. All rights reser ved.