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

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We provide an experimental proof that the so-called `paramagnetic phase’ seen in Fe–Ni-bearing meteorites has a very different electronic structure from that of all other known Fe–Ni minerals, in support of the recent proposal that it is a low moment phase and a new meteoritic mineral. 57 Fe Mössbauer isomer shift measurements, corrected for second-order Doppler shifts, give local electronic densities at the probe nuclei corresponding to a surplus local density of 0.42 electrons per Bohr radius cubed compared to the densities of all other Fe–Ni minerals and all known high-moment synthetic Fe–Ni alloys. This implies that the paramagnetic phase cannot simply be either Fe-rich high-moment face centered cubic phase (taenite) or atomically ordered Fe 3Ni, as previously proposed, and it represents an unprecedented situation where two minerals (the new low moment phase, antitaenite, and taenite) have the same crystal structure and can have the same composition but differ only in electronic structure and associated properties. We also report the bulk production by mechanical alloying of synthetic low-moment Fe–Ni material. These are the first observations of low moment Fe–Ni phases, giving insight into the conditions for metastability and the mechanisms of formation of these unusual alloys.