What we can learn from the hysteresis properties of metal-bearing meteorites

Metallic iron-nickel alloys are the main magnetic minerals in many meteorite groups, mostly in the form of kamacite, taenite and tetrataenite. We present here new room temperature hysteresis measurements on more than a hundred FeNi-bearing meteorite falls, mostly ordinary chondrites, as well as a synthesis of pre-existing data. Low temperature hysteresis measurements (down to 10 K) are also presented. These data are compared to other magnetic (magnetic susceptibility in particular) and petrographic parameters (intensity of thermal metamorphism, shock stage...). The bulk magnetic properties of these meteorites are primarily controlled by the relative proportion of the three above-mentioned minerals, and in particular the presence of tetrataenite. Discussion will focus on, but not be limited to: 1) The the elongated shape of metallic grains that is is revealed by the discrepancy between ferromagnetic susceptibility and saturation magnetization, whose ratio is too high for FeNi alloys; 2) The existence of a low temperature transition around 60 K; 3) The comparison between ordinary chondrites, carbonaceous chondrites, HED achondrites and lunar samples.