Thermomagnetic recording fidelity of nanometer sized iron: implications for planetary magnetism
Abstract
Paleomagnetic observations provide valuable evidence of the strength of magnetic fields present during evolution of the Solar System. Such information provides important constraints on physical processes responsible for rapid accretion of the proto-planetesimal disk. For this purpose, magnetic recordings must be stable and resist magnetic over-prints from thermal events and viscous acquisition over many billions of years. A lack of comprehensive understanding of magnetic domain structures carrying remanence has, until now, prevented accurate estimates of recording fidelity in almost all paleomagnetic samples. Recent computational advances have allowed us to make the first detailed analysis of magnetic domain structures in iron particles as a function of grain morphology, size and temperature. Our results show that uniformly magnetized equidimensional iron particles do not provide stable recordings, but instead larger grains containing single-vortex domain structures have very large remanences and high thermal stability - both increasing rapidly with grain size. We derive curves relating magnetic thermal and temporal stability demonstrating that cubes (>35 nm) and spheres (>55 nm) are likely capable of preserving magnetic recordings from the formation of the Solar System. Additionally, we model paleomagnetic demagnetization curves for a variety of grain size distributions and find that unless a sample is dominated by grains at the super-paramagnetic size boundary, the majority of remanence will block at high-temperatures (∼100°C of Curie point). We conclude that iron and kamacite (low Ni content FeNi) particles are almost ideal natural recorders given that there is no chemical or magnetic alteration during sampling, storage or laboratory measurement
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGP11A..07W
- Keywords:
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- 1521 Paleointensity;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1527 Paleomagnetism applied to geologic processes;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1540 Rock and mineral magnetism;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1595 Planetary magnetism: all frequencies and wavelengths;
- GEOMAGNETISM AND PALEOMAGNETISM