Magnetic Recording Stability of Taenite-Containing Meteorites

Sub-& mu;m taenite and tetrataenite grains observed in a number of (stony-)iron meteorite groups are promising sources of paleomagnetic records in meteorites. While slowly-cooled meteorites form tetrataenite-an extremely good recorder-, fast-cooled meteorites may contain fine-grained taenite, which was considered unsuitable for paleomagnetic studies. In this work, however, we show that nm-sized taenite grains are stable over billion-year timescales, indicating that taenite-bearing meteorites are reliable sources of paleomagnetic information. We find a range of sizes for which taenite forms stable single-domain structures, which coincides with the grain sizes observed in the cloudy zone of most fast cooled IVA meteorites. These meteorites, therefore, can provide reliable paleomagnetic information recorded as a stable crystallization remanent magnetization as taenite grains grown. Vortex states observed in larger (>50 nm) grain sizes are also highly stable, indicating that coarse-grained taenite observed in meteoritic microstructures can also provide reliable records of paleomagnetic fields.