  Iron and its alloys have made modern civilisation possible, with metallic
meteorites providing one of the human's earliest sources of usable iron as well
as providing a window into our solar system's billion-year history. Here
highest-resolution tools reveal the existence of a previously hidden FeNi
nanophase within the extremely slowly cooled metallic meteorite NWA 6259. This
new nanophase exists alongside Ni-poor and Ni-rich nanoprecipitates within a
matrix of tetrataenite, the uniaxial, chemically ordered form of FeNi. The
ferromagnetic nature of the nanoprecipitates combined with the
antiferromagnetic character of the FeNi nanophases give rise to a complex
magnetic state that evolves dramatically with temperature. These observations
extend and possibly alter our understanding of celestial metallurgy, provide
new knowledge concerning the archetypal Fe-Ni phase diagram and supply new
information for the development of new types of sustainable, technologically
critical high-energy magnets.
