Antitaenite is a meteoritic metal alloy mineral composed of iron (Fe) and 20–40% nickel (Ni), (and traces of other elements) that has a face centered cubic crystal structure.
Gamma (fcc) Fe-Ni alloys with low-Ni (about 25% Ni) are probably inhomogeneous on a nanometer scale.
[2] Antitaenite and taenite have the same crystal structure (face centered cubic) and can have the same chemical composition (same proportions of Fe and Ni) but they differ in their electronic structures: taenite has a high magnetic moment whereas antitaenite has a low magnetic moment.
This difference in electronic structure was first established in 1999[3] and arises from a high-magnetic-moment to low-magnetic-moment transition occurring in the Fe-Ni bi-metallic alloy series.
[4] The same electronic structure transition is believed to be a causal factor in Invar behaviour.