tetrataenite

Tetrataenite is a native metal alloy composed of chemically-ordered L10-type , recognized as a mineral in 1980. The mineral is named after its tetragonal crystal structure and its relation to the iron-nickel alloy, taenite, which is chemically disordered (A1) phase with an underlying fcc lattice. Tetrataenite is one of the mineral phases found in meteoric iron. Before its discovery in meteoritic samples, experimental synthesis of the L10 phase was first reported in 1962 by Louis Néel and co-workers, following neutron irradiation of a chemically disordered FeNi sample under an applied magnetic field. Compared to the magnetically soft, chemically disordered A1 phase (taenite), the tetragonal L10 structure of tetrataenite leads to good hard magnetic properties, including a large uniaxial magnetocrystalline anisotropy energy. Consequently, it is under consideration for applications as a rare-earth-free permanent magnet.

== Formation == Tetrataenite forms naturally in iron meteorites that contain taenite that are slow-cooled at a rate of a few degrees per million years, which allows for ordering of the Fe and Ni atoms. It is found most abundantly in slow-cooled chondrite meteorites, as well as in mesosiderites. At high (as much as 52%) Ni content and temperatures below 320 °C (the chemical order-disorder transition temperature), tetrataenite is broken down from taenite and distorts its face centered cubic crystal structure to form the chemically ordered, tetragonal L10 structure. Computational investigations into the phase stability of Fe-Ni alloys have suggested that ferromagnetic ordering plays a key role in making the chemically ordered L10 structure thermodynamically stable.